(Eolumbia  HnitiprHttg 
in  tl|p  (Ettg  of  N^m  fork 

(EoUrgp  of  ^^lyyatriana  a«ft  ^urgrnna 


S^ftr^nr^   IGtbrary 


PLATE  I 


Veinlet-3 


fiftetioles 

and 

Capillatiea 


Diagram  of  Cell-metabolism. 

The  substances  mentioned  on  the  outer  edges  of  the  two  cells  are  some  of  the  materials 
of  cell-anabolism,  while  those  whose  names  are  seen  between  the  cells  are  katabolic  products 
on  their  outward  way  into  the  circulation.  The  red  lines  show  the  locations  of  osmotic 
membranes. 


TEXT-BOOK 


HUMAN  PHYSIOLOGY 


THEORETIC  AND   PRACTICAL 


BY 

GEORGE  V.  N.  DEARBORN,  A.M.  (Harv.),  Ph.D.,  M.D.  (Col.) 

PROFESSOR    OF    PHYSIOLOGY     IN    THE    MEDICAL    AND    DENTAL    SCHOOLS     OF    TUFTS 

COLLEGE,   boston;    PROFESSOR    OF    THE    RELATIONS    OF    BODY  AND  MIND   IN 

THE  SARGENT  SCHOOL  FOR   PHYSICAL    EDUCATION,   CAMBRIDGE,    ETC. 


ILLUSTRATED  WITH   300   ENGRAVINGS  AND  9   PLATES 


LEA    &    FEBIGER 
PHILADELPHIA  AND  NEW   YORK 

1908 


GIFT 

NOV  -  6  1913 

Entered  according  to  the  Act  of  Congress,  in  the  year  1908,  by 

LEA   &   FEHIGER, 
in  the  Office  of  the  LiVjrarlan  of  Congress.     All  rights  reserved. 


JOj  .  (?.  'au..T,y,.^ .  Ofcjt*. 


0 


D  S4- 


^  PREFACE. 


This  book  was  written  primarily  for  medical  and  dental  practitioners 
antl  students.  It  emphasizes,  however,  the  mechanism  of  sense-organs, 
nerves,  and  muscles  as  the  basis  of  the  individual's  efficiency;  and  it  is 
the  first  text-book  of  medical  physiology  to  recognize  the  more  and  more 
insistent  demands  of  the  mental  process.  For  both  of  these  reasons 
it  is  also  especially  adapted  to  the  needs  of  students  and  teachers  of 
physical  education  and  of  psychology. 

The  great  indebtedness  of  the  author  to  some  of  his  colleagues  and 

students  in  the  preparation  of  the  text  and   the  illustrations  is  hereby 

gratefullv  acknowledged. 

G.  V.  X.  1). 


Digitized  by  the  Internet  Archive 

in  2010  with  funding  from 

Open  Knowledge  Commons 


http://www.archive.org/details/textbookofhumanpOOdear 


CONTENTS. 


CHAPTER  I. 
Protoplas.m  axd  the  Cell. 
Protoplasmic  Structure     ..... 

The  General  Properties  and  Nature  of  Protoplasm 

Hypotheses  as  to  the  Origin  of  Life 

Protoplasm  is  not  a  Definite  Chemical  Substance 

Cells 

The  Structure  of  Protoplasm 

Suppositions  as  to  the  Molecular  Structure  of  Protoplasm 

The  Chemical  Composition  of  Protoplasm 

Elements  .... 

Compounds        .... 
Protoplasmic  Function 

Respiration        .... 

Nutrition  .... 

Digestion  .... 

Assimilation       .... 

Excretion  .... 

Irritability  .... 

Movement  .... 

Secretion  .... 

The  Production  of  Energ\- 

Conductivity      .... 

Taxes        ..... 

Consciousness    .... 

Reproduction  and  Growtli   . 

Amitosis  ..... 

Mitosis      ..... 

Heredity  and  Adaptation     . 

An  Example  of  Relatively  Simjjle  Protoplasm:  Ameba 


17 
17 
18 
20 
21 
23 
24 
25 
26 
26 
34 
34 
35 
36 
36 
37 
37 
37 
41 
42 
42 
43 
43 
44 
44 
45 
47 
47 


CHAPTER  II. 
The  Nervous  System. 


The  General  Functions  of  the  Nerxou.s  Sy.^tein 
Features  of  the  Neural  Structure 
The  Chemical  Composition  of  Ner\e-Tissue 
The  Blood-Supply  of  the  Nervous  System 
Functional  Parts  of  the  Nervous  System 

The  Hemispheres 

The  Cerebral  Cortex 

The  Motor  Areas  of  the  Human  Cerebrum 


53 
56 
61 
62 
63 
63 
68 
70 


VI 


CONTENTS 


Functional  Parts  of  the  Xervou 

Tlie  Sensory  Areas 

The  Association-areas 

The  Optic  Thalami 

The  Corpora  Striata    . 

The  Corpora  Quadrigemina 

The  Pons  . 

The  Medulla  Oblongata 

The  Cerebellum 

The  Spinal  Cord 

Conduction 

Distribution  and  Collection 

Reflexion 

Coordination 
Certain  Sets  of  Nerves 

The  Cranial  Nerves 

The  Spinal  Nerves 

The  Sympathetic  Nerves 

Other  Autonomic  Nerves 

The  Nervous  Impulse 


s  System  (continued): 


CHAPTER  III. 

Respiration. 

The  Chemistry  of  Respiration  Proper 
The  Respiratory  Mechanism 

The  Lungs 

The  Capillaries 

The  Thorax 

The  Nerves 
The  Process  and  tlie  Mechanism  of  Internal  Respiration 
The  Sequence  and  the  Causes  of  the  Respiratory  Events 
'i"he  Course  and  the  Kinetics  of  the  Oxj^gen  Inward 
The  Course  and  the  Kinetics  of  the  Carbon  Dioxide  Outward 
ihe  Respiratory  Rhythm  .... 
The  Breath-rate        ..... 
Special  Functions  Connected  with  Respiration 
The  Respiratory  Sounds     .... 
Some  Respiratory  Quantities 
The  Respiration  of  the  P'etus 
liespiration  through  the  Skin 

R<'.spiration  through  the  WnM  of  the  Alimentary  Canal 
Tlie  Quantity  and  Qualit}'  of  the  Air  Required  for  Jvcspiration 


CHAPTER  IV. 
Foods. 

ihe  (leneral  .Nature  of  a  Food  .... 
The  .\nimal  Organism's  Proximate  Principles 
Nutrient  Proximate  Principles 
General  Requirements  in  a  Food   . 


133 
133 
135 
136 


CONTENTS 


Vll 


The  General  Nature  of  Diet       ........ 

A  Source  Both  of  Energ}-  and  of  Tissuo  ..... 

The  Right  Quantitj-  is  Important  ...... 

The  Energj-values of  Foods  ...... 

The  Right  Proportion  of  the  Diet's  Components  is  Important    . 
Variety  in  the  Diet  is  Necessary     ....... 

Cookery    .......••• 

Quantitative  Adaptation  to  its  Service  is  Essential 

Qualitative  Adaptation  in  Certain  Physiological  Conditions  is  Valuable 

Infancy     .... 

Pregnane}'  and  Lactation    . 
Senility     .... 

Idiosyncrasy 

Disease     .... 

Coffee,  Tea,  Cocoa,  Alcohol,  and  Tobacco 


CHAPTER  V 


DiGESTIOX. 


The  Human  Digestive  Mechanism 
Mastication      .... 
Deglutition      .... 
The  Stomacli   .... 
The  Movements  of  the  Stomach 
The  Gastric  Juice 
Digestion  in  the  Stomach 
The  Stomach's  Functions  . 
The  Small  Intestine 
The  Movements  of  the  Small  Intestine 
Pancreatic  Juice 
Intestinal  Juice 

Bile 

The  Large  Intestine 

The  Movements  of  the  Large  Intestine 

Digestion  in  the  Large  Intestine 


CHAPTER  VI. 

Nutrition. 


Absorption       .... 
Metabolism      .... 

Organic  Growth  and  Repair 

Secretion 

Osmosis    .... 

"Vitalism" 

The  Phenomena  of  Secretion 

The  Internal  Secretions 

Animal  He.it 

Human  Temperature 


VUl 


CONTEXTS 


Metalvjlism  (continued) : 

Tliermotaxis      ..... 

Tlie  Means  of  Regulating  Heat-production 

The  Regulation  of  Thermolysis 

The  Thermotactic  Nerves  , 
Other  Forms  of  Energy-expense 
Excretion  .... 
The  Urine        .... 

The  Composition  of  the  Urine 

The  Excretion  of  Urine 

The  Discharge  of  Urine 
The  Expired  Air 
The  .Sweat        .... 
The  Feces 


CHAPTER  VII. 

The  Blood  and  the  Lymph. 


The  Chemical  Composition  of  the  Blood  and  Lymph 
The  Chemical  Components  of  the  Plasma  and  Lj'^mph 
The  Chemical  Components  of  the  Erj-throcytes 
The  Chemical  Components  of  the  Leukocytes 
The  Chemical  Components  of  the  Thrombocytes 

Whole  Blood 

Coagulation     ..... 

The  Physical  Constitution  of  the  Blood  and  Lymph 
The  Erythrocytes     .... 

The  Leukocytes        .... 

The  Thromboc)i,es  .... 

Lymph    ...... 

The  Formation  of  Lymph 

The  Physical  Constitution  of  Lymph 

The  Quantity  of  the  Lymph 

The  Functions  of  the  Lymph 


CHAPTER  VIII. 

The  Circulation. 


The  Causes  of  the  Circulation 

The  Contraction  of  the  Heart 
The  Recoil  of  the  .\rterial  Walls 
Thoracic  Suction 

Compression  by  the  Body-muscles 
The  Suction  of  the  Relaxing  .\uricles 

The  Speed  of  the  liiood-current 

The  Circulation-time 

The  Pulse-wave 

Blof»d -pressure 

The  Pulse-rate  of  the  Heart 

The  Cardiac  Sequence 


CONTENTS 


The  Sounds  of  the  Heart  . 

The  Heart-beat  as  Muscular  Action    . 

The  Influence  of  Nerves  on  the  Heart 

The  Sympathetic  Influence 

The  Influence  of  the  Vagus 

The  Afferent  Nerve  of  the  Heart 

Cardiac  Centers 
The  Functions  of  the  Blood-  and  Lyinph-vesseh 
The  Physiology  of  the  Arteries  . 
The  Pulse         ..... 
Vasomotion     ..... 
The  Functions  of  the  Blood-capillaries 
The  Lymphatic  Portion  of  the  Circulation 
The  Causes  of  the  Lymph-flow  . 
The  Functions  of  the  ^'eins 


CHAPTER  IX. 

The  Skin. 


The  Functions  of  the  Skin 
Protection 
Sensation 
Thermotaxis 
The  Sweat 

The  Secretion  of  Sebum 
Respiration 
Absorption 
Coloration 
The  Hairs  and  the  Nails 


CHAPTER  X. 


The  Senses. 


Kinesthesia     ..... 

Afferent  Endings  in  Muscle 

Afferent  Endings  in  Tendons 

Afferent  Endings  in  the  Joints,  etc. 

Kinesthetic  Function 
Vision      ...... 

The  Receptive  Apparatus  of  the  Eye 

The  Various  Adjustments  of  the  Eyes 

Head-movements 

Eje-movements 

Accommodation 

Visual  Theories 

The  Perception  of  Light 

Theories  of  Color-vision 

Color-blindness 

Space-perception 


cox  TEXTS 


llearing  ......... 

The  Transmitting  A|)pai;itus  and  Functions  of  the  Ear 

The  Organs  of  Corti   . 

How  Does  the  Organ  of  Corti  Act? 

Certain  Quahties  of  Sounds 

The  Perception  of  Obstructions   . 
Touch,  I'ressiu'e,  and  Location 

Organs  and  Functions 

Toucli-spots       .... 

Certain  Tactual  Quahties    . 
Taste 

The  Gustatory  Apparatus 

The  Taste-buds 

Tlie  Nerves  of  the  Sense  of  Taste 

Some  Characteristics  of  Taste 
Smell 

The  Olfactory  Apparatus    . 

The  Olfactory  Cells    . 

The  Regio  Olfactoria 

The  Nerves  of  Smell  . 

Some  Conditions  of  Smell    . 
The  Temperature-senses   . 

The  Apparatus  of  the  Temperature-senses 
Pain        ...... 

The  Sensory  Apparatus  of  Pain   . 

Pleasure  ..... 

Vertigo  ...... 

Fatigue,  Thirst,  and  Hanger 

Fatigue 

Thirst        .... 

Hunger     ..... 

Nausea      ..... 


CHAPTER  XI. 

MuscuL.\R  Action. 


The  Contractile  System  in  .Man 
The  Structure  of  Muscle    . 

Smooth  Muscle 

Cro.ss-.striated  Muscle. 

Cardiac  Mu.sde 
Till'  Ciiemistry  of  Muscle  . 
The  .Modes  of  Action  of  Mu.scle 

The  Thermo-<lynamic  Theory 

The  Chemi-surface-tension  'I'lietjr 

The  Neuro-niuscular  Mechanism 
Special  Muscular  I'lmctions 

Posture     . 

Standing  . 

Sitting       . 

Locomotion 

Walking  and  Huniring 


CO  STENTS 


Xl 


Speech    ... 
The  [{expiratory  licUow; 
The  Larynx 
The  Air-chambers 
The  Nervous  Control 
Aphasia 

Emotional  Reactions 


CHAPTER  XII. 

Mental  Function. 

The  "Functions"  of  the  Mental  Process 

Certain  General  Characteristics  of  the  Mental  Process 

The  Descriptive  Aspects  of  Consciousness 

Feeling     .... 

Sensation 

The  Feelings  and  Emotions 
Willing 

Habit  and  Instinct 
Knowing  .... 

Sensation 

Perception 

Conception 

Understanding  . 

The  Reason 
The  Relations  of  Body  and  Mind 
Memory  .... 

Sleep       ..... 
Hallucinations,  Illusions,  and  Delusions 
Anesthesia        ..... 


CHAPTER  XIII. 

Reproduction  and  Development. 

Puberty  and  Menstruation 

Puberty  in  the  Male  . 

Puberty  in  the  Female 

Ovulation 

Menstruation 

The  Relation  of  Ovulation  to  Menstruation 
Impregnation 

Coitus 

Semen 

Fertilization 

Oviposition 
Preinancy,  Parturition,  and  Lactation 

Pregnancy  ..... 

The  Changes  in  the  Reproductive  Organs 

Alterations  in  the  Body  Generalh' 

Mental  Changes  .... 

Parturition         ..... 

Lactation  ..... 


Xll 


CONTENTS 


Development  . 
Fetal  Life 
Childhood 
Maturity  . 
Old-age 
Death 


448 
449 
449 
453 
454 
456 


APPENDIX. 

Laboratory  Physiology     ..... 

List  of  Topics  for  Dissertations  and  Conference  . 
Tables    ........ 

Index      ........ 


459 
530 
533 
537 


HUMAN  PHYSIOLOGY. 


CHAPTER    I. 

PROTOPLASM  AND  THE  CELL. 

The  tissues  of  animals,  including  man,  are  made  up  of  a  substance 
which  is  variously  termed  protoplasm,  bioplasm,  and  sometimes  biogen. 
Protoplasm  as  found  in  the  bodies  of  the  more  highly  developed  animals 
is  variously  changed  ("differentiated")  to  adapt  it  to  many  special 
functions,  so  that,  as  may  be  seen,  it  is  often  hard  to  recognize  the  typical 
protoplasm  in  the  many-colored  tissues  of  a  man:  bone,  muscle,  epi- 
thelium, nerve,  etc.  The  bodies  of  human  beings,  then,  are  made  of 
highly  differentiated  sorts  of  protoplasm,  each  developed  for  some 
particular  purpose  in  some  special  way.  The  functions  of  each  can  be 
understood,  however,  only  when  the  fundamental  general  nature  of  all 
protoplasm  has  been  learned.  It  is  for  this  purpose  that  a  chapter  will 
be  devoted  to  the  composition,  structure,  and  general  functions  of 
protoplasm. 

PROTOPLASMIC  STRUCTURE. 

The  General  Properties  and  Nature  of  Protoplasm. — As  seen  with  the 
naked  eye,  or  under  a  low  degree  of  enlargement,  undifferentiated 
protoplasm  appears  as  a  nearly  transparent,  usually  colorless,  viscid 
lif|uid.  It  is  entirely  insoluble  in  water.  It  is  coagulated  and  killed  by 
many  agencies,  e.  g.,  by  about  50°  C.  of  heat,  by  alcohol,  strong  acids, 
alkalies,  and  many  other  chemical  substances;  it  is  disorganized  by 
powerful  currents  of  electricity.  Its  specific  gravity  is  about  1250;  that  is, 
protoplasm  is  about  one-quarter  heavier  than  water.  Seen  under  the 
microscope,  it  reflects  light  nearly  as  actively  as  does  oil.  The  most 
important  characteristic  of  protoplasm  physically  is  its  colloidal  fluidity, 
the  consistence  being  such  that  it  will  flow  freely  and  yet  retain  its  proper 
shape,  as  determined  by  the  sort  of  cell  or  animal  which  it  composes. 
Xo  property  is  more  essential  to  living  matter  than  this,  for  movement, 
the  prime  external  attribute  of  all  life,  depends,  of  course,  directly  on 
the  mobility  of  protoplasm,  on  the  freedom  of  the  motion  of  particle  on 
particle. 

Protoplasm  is  dependent  on  heat  for  its  activity,  which  is  greatest  at 
2 


Ig  PROTOPLASM  AXD  THE  CELL 

a  temperature  of  about  30°  C.  and  decreases  with  lessening  temperatures 
down  to  the  freezing-point  of  water.  When  0°  C.  is  nearly  reached, 
movements  apparently  cease  altogether,  although  vital  molecular  move- 
ments doubtless  continue.  Certain  forms  of  life,  especially  some  spores 
and  many  kinds  of  bacteria,  endure  even  the  cold  of  liquid  air  and  that 
of  other  still  colder  solidified  gases,  reviving  uninjured  when  allowed  to 
become  warm  again. 

Such  are  some  of  the  more  important  external  characteristics  of  the 
physical  basis  of  life,  that  is,  of  the  quasi-undifferentiated  protoplasm 
which  composes  many  of  the  infusoria,  etc.  Differentiated  protoplasm, 
comprising  the  tissues  of  animals  of  more  complex  structure,  has  many 
other  colors,  specific  gravities,  consistencies,  and  physical  qualities, 
many  of  which  are  described  by  the  science  of  histology. 

Fig.   1 

Food  vacuole 

,  Vacuole. 


JTucleus. o'  3    s'y 


Ameba  proteus.  The  nucleus,  cytoplasm,  metaplasm,  "  endoplasm,"  "  ectoplasm,"  contractile 
vacuoles,  food-vacuoles,  other  vacuoles,  new  and  old,  are  easily  made  out.  Oftentimes,  besides, 
these  formless  masses  of  food  debris  are  to  be  seen  colored  green,  yellow,  or  red.      X  60. 

Hypotheses  as  to  the  Origin  of  Life. — About  the  origin  of  life,  especially 
on  this  planet,  there  has  always  been  much  speculation,  and  we  may  well 
mention  the  four  or  five  leading  hypotheses,  only  one  of  which,  however — 
the  last — tends  slowly  to  .some  degree  of  present  confirmation:  (1)  One 
theory  of  the  source  of  tcrrestial  life  may  be  read  in  the  first  chapter  of 
Genesis.  •  It  is  obvious  that  such  an  allegorical  account  of  the  matter, 
however  picturesque,  has  little  scientific  interest  in  the  light  of  evolu- 
tionary philo.sophy,  for  the  account  fails  to  state  h-ow  the  creation  was 
performed,  which  in  it.self  is  the  problem.  (2)  The  theory  of  hylozoism, 
that  the  world  itself  is  inherently  alive  and  that  the  inorganic  is  conse- 
f|uently  secondar}^  to  the  organic,  has  much  philo.sophical  interest,  but 
little  present  proof  or  importance  as  a  scientific  theory.  (3)  H.  E. 
Rirhter,  T>orfl  Kelvin,  and  even  the  great  Helmholtz,  discussed  the 
proposition  tliat  life  is  eternal  and  that  its  germs  came  to  earth  in  meteors 
or  in  other  ways  from  other  planetary  .specks  in  the  universe.     This 


PROTOPLASMIC  STRUCTURE  ig 

theory  obviously  but  transfers  the  biological  problem  from  this  planet 
to  some  other.  (4)  For  twenty  centuries  and  more  the  theory  of  spon- 
taneous generation  was  usually  accepted,  and  Aristotle,  founder  of 
biology,  shared  the  belief.  This  notion  was  simply  that  life  originated 
continually  from  non-living  matter.  This  was  the  natural  and  inevitable 
conviction  in  days  when  there  were  no  microscopes,  or  none  powerful 
enough  to  show  the  germs  of  animals.  Today,  without  at  all  denying  the 
possibility,  past,  present,  or  future,  of  the  spontaneous  origin  of  life  from 
inorganic  matter,  we  are  almost  satisfied  to  believe  that  every  animal, 
as  also  every  plant,  at  present  originates  in  one  way  or  another  only  from 
more  or  less  similar  living  parents  or  parent.  In  other  words,  most 
biologists  nowadays  suppose  that  protoplasm  (and  by  the  term  proto- 
plasm we  mean  all  living  matter)  springs  only  from  germs  and  germ- 
plasm.  (5)  In  1S66  Ernst  Hackel  suggestefl  that  from  analogy  it  was 
proper  to  assume  that  life,  or  at  least  living  forms,  did  begin  to  develop 
at  some  time  or  other  in  the  earth's  evolution  from  unorganized,  non- 
living matter.  This  is  the  supposition  which  at  present  receives  the  most 
attention  from  biologists  as  the  probably  true  theory.  Pfliiger  accepts 
this  hypothesis,  and  has  materially  developed  it  by  suggesting  (1875)  that 
in  the  vast  chemical  intermingling  of  the  slowly  cooling  world  there  was 
early  a  union  of  the  elements  carbon,  hydrogen,  oxygen,  nitrogen,  and 
sulphur  in  a  way  which  made  possible  the  phenomena  we  called  life 
in  the  new  substance  so  produced.  Pfliiger,  indeed,  goes  farther  in 
hypothesis,  and  postulates  that  the  combination  characteristic  of  life  in 
its  last  analysis  is  cyanogen  (CN),  the  union  of  carbon  and  nitrogen. 
All  the  decomposition-products  of  protoplasm  (for  example,  urea,  creatin, 
guanin,  uric  acid)  hold  this  cyanogen  radicle  or  group,  and  this  is  good 
evidence  that  living  protoplasm  always  contains  it  also,  while  it  is  likely 
that  ^'dead  protoplasm"  does  not.  Cyanic  acid,  CXOH,  Pfliiger  points 
out,  is  like  protoplasm  in  many  respects:  it  is  fluid  and  transparent  at 
low  temperature,  coagulating  by  heat;  both  break  up  into  carbon  dioxide 
and  ammonia;  and  both  produce  urea  by  dissociation.  "The  similarity 
of  the  two  substances  is  so  great  that  I  might  describe  cyanic  acid  as  a 
semiliving  molecule."  Cyanogen  and  its  compounds  are  formed  only  at 
incandescent  heat,  such  as  surely  obtained  on  the  earth  in  its  early 
stages  of  cooling,  and  others  of  the  components  of  protoplasm  are  made 
under  a  like  condition.  Perhaps  a  further  quotation  of  Pfliiger's  words 
will  best  represent  his  ideas:  "Thus,"  he  says,  "nothing  is  clearer  than 
the  possibility  of  the  formation  of  cyanic  compounds  when  the  earth  was 
entirely  or  partially  in  a  state  of  incandescence  or  great  heat.  We  see 
how  extraordinarily  all  the  facts  of  chemistry  point  to  fire  [see  Heraclitus!] 
as  the  force  that  has  produced  the  constituents  of  albumin  by  synthesis. 
Hence  life  was  born  from  fire,  and  the  chief  conditions  of  its  appearance 
are  associated  with  a  time  wlien  the  earth  was  a  gflowino:  ball  of  fire. 
nTien  we  remember  the  incalculably  long  period  in  which  the  surface 
of  the  earth  was  cooling,  we  see  that  cyanogen,  and  the  compounds  that 
contained  cyanogen,  and  carburetted  hydrogen  had  sufiicient  time  and 


20  PROTOPLASM  AXD   THE  CELL 

opportunity  to  follow  out  to  anv  extent  their  great  tendency  to  the  trasn- 
position  and  formation  of  polymeria  (chains  of  atoms),  and,  with  the 
cooperation  of  oxygen  and  afterward  of  water  and  salts,  to  evolve  into 
the  self-decomposable  albumin,  which  is  living  matter."  In  unlimited 
time  unlimited  adaptation  might,  indeed,  be  rationally  postulated.  How 
great  the  number  of  millions  of  years  involved  in  this  particular  part  of 
evolution  no  man  can  accurately  estimate.  Now,  as  well  as  then,  Pfiiiger, 
Hackel,  and  Verworn  suppose  it  is  cyanogen  which  introduces  into  living 
matter  its  "energetic  internal  motion,"  the  essential  of  life,  known  in 
phvsiology  as  metabolism.  (This  process  is  defined  below:  see  page  35.) 
There  is  nothing,  however,  in  such  a  supposition  to  disprove  the  con- 
tinued generation  anew  of  protoplasm  today.  As  will  be  seen  when  we 
discuss  a  special  form  of  protoplasm,  muscle,  the  degree  of  heat  which 
mav  obtain  in  scattered  molecules  of  a  mass  of  living  matter  is  unlimited. 
It  may  be  high  enough  to  allow  of  the  production  of  new  protoplasm 
from  these  molecules  situated  here  and  there  in  the  living  matter.  The 
chemi-atomic  action,  oxidation,  may  be  violent,  and  yet  the  relative 
mass  of  these  molecules,  although  far  too  small  to  effect  any  considerable 
amount  of  living  substance,  may  perhaps  be  large  enough  to  generate 
anew  a  particle  of  protoplasm  endowed  with  life. 

Other  biological  thinkers  have  supposed  that  there  is  a  molecular 
union  of  some  sort  characteristic  of  the  carbohydrate  molecule  also, 
since  this  seems  to  be  present  in  every  form  of  protoplasm,  however  small, 
as  will  be  further  seen  below. 

Such,  in  brief,  are  the  most  prominent  theories  as  to  the  origin  of  life 
on  the  earth.  A  combination  of  the  last  two  hypotheses  discussed  is 
certainly  not  unreasonable  from  any  point  of  view. 

Protoplasm  not  a  Definite  Chemical  Substance. — It  is  necessary  to  have 
one  idea  in  mind  continually  in  studying  the  nature  of  protoplasm — 
namely,  that  it  is  a  morphological  substance  rather  than  a  definite  chemi- 
cal compound.  ^J'o  explain  the  meaning  of  this  rather  important  state- 
ment, we  may  well  consider  what  the  word  protoplasm  does  not  mean. 
The  term  is  not  a  physical  notion.  One  does  not  think  of  protoplasm 
as  a  substance  with  an  unchangeable  set  of  physical  properties  or  qualities, 
such  as,  for  example,  diamond  or  alcohol.  Again,  protoplasm  is  not  a 
definite  chemical  sul>stance.  AVhile  it  has,  of  course,  some  definite 
chemical  comfjosition  at  any  one  instant,  still  that  composition  is  so 
enormously  complex  that  no  chemist  can  learn  it.  Its  extreme  lability 
or  changefulness  is  a  thing  entirely  characteristic  of  protoplasm,  so  much 
so  that  we  cannot  think  of  it  as  a  chemical  substance  in  the  common 
usage  of  that  term.  rrotoj)Iasm,  again,  is  not,  strictly  sp(>aking,  an 
anatomical  substance,  one  with  an  absolutely  definite  structure  like  the 
femur  or  the  kidney.  It  is  not,  finally,  a  physiological  substance,  one  with 
a  definite  set  of  invariable  functions  like  the  eye  or  the  stomachs  of 
cattle.  We  learn  to  think  of  ])n)to[)lasm  as  a  certain  general  colloidal 
sort  of  living  matter  with  certain  characteristics  and  structure  too  com- 
plex to  be  easily  defined. 


PROTOPLASMIC  STRUCTURE 


21 


Fir;.  2 


m 


0 


Cells. — Animal  bodies  are  made  up  of  tissues.  Tissues  are  divided 
into  orii;ans.  Organs  are  composed  of  cells,  which  in  turn  have  biological 
divisions.  At  the  risk  of  impinging  to  some  extent  on  histology,  we  must 
look  (l)ut  briefly)  at  the  parts  which  make  up  cells,  as  an  intnxhiction  to 
the  study  of  the  composition  and  the  properties  of  protoplasm.  In  1G65 
(the  famous  year  of  the  great  London 
plague)  Robert  Hook,  an  English  nat- 
uralist, discovered  organic  cells  in  vege- 
table tissues.  He  named  them  cells 
because  the  little  "chambers"  seemed 
to  him,  using  the  rude  microscopes  of 
the  day  (discovered  only  fifty  years 
before),  like  hollow  and  empty  cavi- 
ties. A  dozen  years  later,  Malpighi, 
the  Italian  anatomist,  recognized  that 
these  elements  were  masses  of  tissue, 
each  with  walls  of  its  own,  so  that,  after 
all,  the  animal  cell  is  a  chamber, 
although  one  largely  filled  with  liquid. 

A  living  cell  in  general  is  made  up  of 
at  least  four  or  five  parts,  cytoplasm, 
nucleoplasm,  or  nucleus,  the  centrosome 
within  the  attraction  sphere,  and  some- 
times, if  not  always,  a  limiting  mem- 
brane. The  cytoplasm  consists  of  a 
homogeneous,  semifluid,  and  somewhat 
transparent  mass  (the  enchylema),  and, 
variously  arranged  within  this,  other 
perhaps  more  solid  masses  or  lines  or 
granules  of  a  different  nature.  The 
nucleoplasm  is  composed  of  a  nuclear 
sap,  the  enchylema,  a  linin  network, 
various  chromatic  masses  of  nuclein, 
and  a  nucleolus.  About  all  these, 
dividing  it  from  the  surrounding  cyto- 
plasm, is  a  nuclear  membrane.  The 
centrosome  and  the  attraction-sphere 
containing  it  (concerned  especially  in 
reproduction)  are  apparently  permanent 
organs  of  the  cell;  they  are  seen  most 
often  and  most  plainly  at  the  time  of 
the  division  of  the  cell.  To  some  observers  the  centrosome  appears  as 
the  center  of  activity  of  the  cell. 

That  the  cells  of  animals  and  plants  have  nuclei  was  discovered  by 
Fontana  in  1781.  The  nucleus  of  a  cell  is  usually  a  rounded  mass,  but 
it  may  have  other  forms,  as  in  vorticella  (c-shaped)  and  the  distributed 
granular  form  of  certain  rhizopods.     It  usually  constitutes  but  a  small 


mm 


chdn 


c 


pj 


:saB 


m 


,kD 


s^te! 


■4 


Radial  section  in  the  wood  of  a  young 
spruce,  to  show  the  vegetable  tvTse  of  cell 
and  also  the  circulatory  mechanism  of  a 
plant.  (U.  S.  Dept.  of  Agriculture, 
Farmers'  Bulletin,  No.  173.) 


22 


PROTOPLASM  AXD  THE  CELL 


part  of  the  entire  cell,  but  in  this  respect,  also,  the  nucleus  varies  largely. 
In  some  sorts  of  leukocytes,  for  example,  the  nucleus  largely  fills  the 
cell-wall.      In  one  respect  only  is  the  nucleus  constant — namely,  in  its 


Fig.  3 
Attraction  sphere  enclosing  the  centrosomes. 


Nucleus  < 


Plasmosome  or 
true  nucleolus. 

Chromatin- 

network. 
Linin-network. 

Karyosome    or 
net-knot. 


Plastids     Ijang    in 
the  cytoplasm. 


tvf 

r-'t^ 

%J, 

.-J-?,^ 

■(l\~ 

W#*v  >  •  •  ••  • 


Vacuole. 


-Lifeless      bodies 
(metaplasm)  sus- 
pended     in      the 
cytoplasmic       re- 
ticulum. 


Diagram  of   a  cell.      (Wilson.) 


presence  in  some  place  and  form  and  size  in  every  living  cell.  To  this 
there  is,  for  purposes  of  definition,  no  exception,  for  the  erythrocytes 
(see  page  263)  are  not  called  cells,  but  corpuscles,  because  they  seem  at 
present  to  have  no  nuclei.     The  nuclear  sap  is  indistinguishable  in  its 


Fig.  4 


.^% 


J 


A  bit  of   the  nucleus  of   the  iiifusorian  Stylonichia.     (Pesrtoureau.) 

nature  from  the  similar  licpu'd  of  the  cytoplasm.  The  linin  network  is  an 
extremely  delicate  structure  that  does  not  stain  with  the  ordinary  dyes. 
C.  Schneider  maintains  that  the  filaments  of  linin  are  continuous  through 


PROTOPLASMIC  STRUCTURE  23 

the  nuclear  membrane  with  the  fibers  in  the  cytoplasm,  while  Stras- 
biirger  believes  in  its  structural  independence  of  the  cytoplasm.  The 
masses  of  chromatin,  so  conspicuous  in  many  stained  nuclei,  are  much 
more  sui)stantial  than  the  linin  network  on  which  they  are  distril)uted. 
The  exact  relations  of  these  two  nuclear  elements,  the  linin  network  and 
the  chromatic  masses,  are  still  in  doubt,  but  in  one  way  or  another  they 
are  surely  structurally  connected.  By  some  competent  observers,  espe- 
cially by  certain  neurologists,  the  chromatin  bodies  are  considered  to  be 
chemically  the  most  essential  part  of  the  nucleus.  The  nucleolus  may  be 
only  one,  or  there  may  be  many,  sometimes  bunched  together  into  what 
seems  a  solid  mass.  These  are  situated  in  the  nuclear  sap,  and  are  uncon- 
nected and  unattached  to  either  the  linin  network  or  to  the  chromatic 
granules.  The  nuclear  membrane,  dividing  the  nucleoplasm  from  the 
cytoplasm,  is  very  delicate  and  perfectly  transparent.  Through  it  the 
important  interchanges  of  the  nucleus  and  the  cytoplasm  continually 
take  place. 

The  cytoplasm  constitutes  much  the  larger  mass  of  the  majority  of 
cells.  In  structure  it  appears  to  be  much  simpler  than  the  nucleoplasm, 
having  only  two  elements,  a  reticulum  (or  something  similar  in  appear- 
ance) and  a  homogeneous  transparent  fluid  pervading  and  surrounding 
it.  Leydig  and  Schafer  suppose  the  more  liquid  portion  to  be  the  essen- 
tial part,  but  many  authorities  so  consider  the  network  or  reticulum. 
Some,  of  late,  have  maintained  that  the  "reticulum"  is  artificial.  A 
more  reasonable  supposition,  however,  is  to  recognize  in  both  indispen- 
sable ingredients  of  the  vital  substance. 

The  Structure  of  Protoplasm. — This  has  been  discussed  by  many 
biologists,  but  the  results  of  their  work  are  so  various  that  their  theories 
are  of  slight  importance.  The  difierences  in  what  observers  describe  as 
seen  under  the  high  powers  of  the  microscope  depend  more  on  mental 
differences  than  on  anything  else.  This  is  a  good  illustration,  as  modern 
psychology  has  pointed  out,  that  what  one  sees,  or  thinks  he  sees,  depends 
to  a  considerable  extent  on  the  contents  of  his  mind.  The  most  likely 
supposition  is  that  identified  with  the  names  of  Kolliker,  Kiinstler,  and 
especially  of  Biitschli.  The  researches  of  Biitschli  are  classical,  par- 
ticularly those  in  which  he  has  imitated  w^ith  emulsions  the  movements 
of  some  varieties  of  protoplasm.  On  this  supposition  protoplasm,  or 
at  least  cytoplasm,  consists  of  a  mass  of  minute  spheres  filled  w'ith  trans- 
parent lic[uid,  these  being  crowded  together  so  closely  that  their  liquid 
walls  coalesce  and  form  lines  more  or  less  straight  and  angular.  It  is 
only  because  of  the  optical  conditions  that  the  largest  of  these  inter- 
secting spherules  appear  to  constitute  a  network.  The  spherules  are 
freely  movable  and  roll  upon  each  other  without  breaking  the  continuity 
of  the  protoplasmic  element  w'hich  forms  their  walls.  These  exceedingly 
minute  droplets  of  liquid  (called  chylema  by  Biitschli)  are,  according  to 
this  theory,  the  essential  elements  of  protoplasm,  ^^'hether  the  fine 
fibrils  and  the  minute  o-ranules  which  sometimes  are  to  be  found  in  the 
liquid  between  the  droplets  are  incidental,  or  have  some  secondary  func- 


24 


PROTOPLASM  AND   THE  CELL 


tion,  is  at  present  unknown.  Such  is  the  hypothesis  as  to  the  structure 
of  bioplasm  which  is  proVnihly  the  most  accepted  tothiv  among  biologists 
and  cytologists.  None  the  less,  at  the  present  stage  in  the  development 
of  human  biological  knowledge,  the  physical  structure  of  protoplasm 
involves  many  doubts  and  mysteries. 

SiH^positions  as  to  the  Molecular  Structure  of  Protoplasm. — There  have 
been  pul)lished  one  or  two  supj)ositions  concerning  the  molecular  or  ultra- 
visible  structure  of  protoplasm  which  are  worthy  of  repetition.  They  serve 
to  fix  the  imagination,  thus  giving  it  a  useful  basis  to  start  with,  a  condition 
much  better  than  absolute  vacuity.    In  lieu  of  the  certain  truth,  a  reason- 


Theories  as  to  the  physical  structure  of  protoplasm.  In  the  center  is  represented  the  structure 
of  a  nucleus:  1,  the  granular  theory;  2,  the  filament  theory;  3,  the  foam  (or  vacuole)  theory; 
4,  the  reticular  theor>';  5,  some  of  the  crystals,  etc.,  found  in  bioplasm  at  various  times. 
(H.  K.  Richardson.) 


able  h^'pothesis  is  much  lietter  than  nothing;  "mere  hypotheses"  have 
often  established  their  high  value  to  science.  C.  Nageli  is  the  inventor 
of  the  micellar  theory  of  the  ultimate  structure  of  protoplasm.  It  is  a  sup- 
posit'on  merely,  but  a  pertinent  one.  As  atoms  combine  to  form  mole- 
cules, according  to  the  atomic  theory  (long  accepted,  though  never  proved), 
.so  Xageli  imagines  Uiat  in  the  case  of  living  matter  these  molecules 
unite  in  groups  to  form  still  more  comjilex  units,  which  he  names  micellae. 
P^ach  micella  is  suj>posed  to  be  made  of  hundreds  or  of  thousands  of 
molecules,  although  even  then,  large  as  the  vital  molecules  surely  are, 
they  are  too  small  to  be  seen  with  any  instrument  now  known,  or  even 
with   the   ultraviolet   rays.      In    protoplasm    flic   iiiieclla'  unite   to  form 


PROTOPLASMIC  STRUCTURE  25 

regularly  arranged  groups,  in  which  the  individual  micellfe  may  consist 
of  similar  or  of  different  chemical  substances,  and  may  vary  largely  in 
shape  and  in  size.  The  micellae  may  unite  in  clusters  within  the  group, 
so  that  a  group  may  consist  of  smaller  groups,  and  these  smaller  groups 
seem  to  tend  to  form  chains.  These  little  lines  or  chains  unite  in  a  net- 
work, with  large  or  small  meshes,  as  the  case  may  be.  In  these  meshes 
is  the  water  which  gives  to  protoplasm  its  important  nature  as  a  colloid 
(on  which  many  of  the  vital  functions  depend:  see  page  25).  Nageli 
discriminates  three  conditions  in  which  the  water  of  the  colloidal  proto- 
plasm may  exist  in  relation  to  the  micellae:  the  water  of  constitution  or  of 
crystallization,  the  water  of  adhesion,  and  capillary  water.  The  first 
is  as  proper  a  part  of  the  micellae  as  is  the  water  of  a  crystal;  the  water 
of  adhesion  is  that  held  close  to  the  micellae  by  molecular  attraction;  the 
capillary  water  is  that  lymph  filling  up  the  meshes  of  the  network  outside 
the  sphere  of  attraction  of  the  micellae.  Other  substances  besides  water 
may  be  firmly  held  to  the  micellae,  such  as  calcium  salts,  dyes,  nitrogenous 
and  carbohydrate  substances  previously  dissolved.  Growth  is  accounted 
for  in  this  way. 

On  the  other  hand,  W.  B.  Hardy  has  recently  published  a  theory 
based  on  the  nature  and  activity  of  the  ions.  (Ions  are  groups  of  atoms 
or  dissociated  parts  of  molecules  which  carrv  charges  of  electricity  and 
so  by  their  presence  make  a  solution  an  electrolyte.  All  circulating 
animal  and  vegetal  liquids  are  electrolytes,  and  these,  being  alkaline  and 
pervading  the  tissues,  make  the  latter  electrolytes  and  alkaline  also.) 
Hardy  supposes  that  bioplasm  is  made  up  of  groups  of  about  ten  thousand 
complex  molecules.  These  groups  (termed  "particles")  are  held  by 
electrical  equilibrium  in  suspension  in  water.  Protoplasm  is  thus  a 
"hydrosol,"  and  a  hydrosol  of  the  reversible  type.  Each  particle  or  group 
of  molecules.  Hardy  supposes,  is  surrounded  by  a  double  layer  or  zone 
of  ions  charged  with  electricity,  the  repulsion  between  the  particles 
keeping  up  the  normal  fluidity  of  the  protoplasm.  When  the  difi'erence 
of  potential  is  changed  the  density  of  the  hydrosol  is  altered  in  part  by 
means  of  the  chemical  reactions  between  contiguous  molecules,  these 
reactions  altering  the  electrical  status  of  the  ionic  zones  surrounding  each 
particle.  Thus  we  have  coagulation  and  decoagulation.  This  theory 
also,  though  unsubstantiated,  has  no  little  interest  in  view  of  the  impor- 
tance in  physiology  of  the  doctrines  of  the  osmosis  and  solution  of  salines. 

The  Chemical  Composition  of  Protoplasm. — If  the  physical  structure 
and  action  of  protoplasm  are  involved  in  many  doubts  and  almost  as 
many  hypotheses,  certainly  its  chemical  composition  is  surrounded  by 
more.  Not  but  that  we  know  the  chemical  "elements"  entering  into 
protoplasm,  for  these  persist  after  its  death  and  may  be  readily  deter- 
mined; nor  yet  but  that  some  of  the  substances  in  protoplasm  have  been 
identified.  It  is  the  exact  chemical  arrangement  of  these  elements  and 
these  complex  substances,  how  they  are  combined  and  especially  how 
they  differ  in  the  living  and  the  dead,  that  baffle  the  skill,  ingenuity,  and 
deft  technique  of  the  biochemists.     The  last  suggested  problem  is  the 


26  PROTOPLASM  AND  THE  CELL 

most  important — indeed,  "dead  protoplasm"  is  a  contradiction  in  terms, 
and  protoplasm  when  it  has  died,  whatever  that  means,  is  no  'onger 
protoplasm  but  only  a  mass  of  matter  hastening  toward  decomposition. 
We  may  be  almost  sure  that  it  is  then  quite  unlike,  in  its  essentials  of 
chemical  structure,  the  composition  of  the  same  substance  when  alive. 
This  problem  of  the  analysis  of  protoplasm  is,  indeed,  difficult,  for  when 
one  applies  any  of  the  methods  and  reagents  of  analysis  now  known,  the 
mass  of  protoplasm  or  biogen  is  forthwith  no  longer  living  but  dead,  and, 
therefore,  changed  in  those  very  respects  about  which  the  chemist  and  the 
physiologist  seek  to  learn.  Here,  again,  is  a  field  for  shrewd  hypothesis 
— a  field  that  has  been  well  cultivated,  as  almost  any  physiological 
chemistry  will  show.  It  begins  to  be  obvious  that  by  synthesis,  rather 
than  by  analysis,  the  composition  of  protoplasm  will  be  learned. 

Elements, — Of  the  chemical  "elements,"  numbering  about  eighty, 
there  are  a  dozen  which  seem  to  be  present  without  exception  in  all 
protoplasm,  primal  and  differentiated.  These  twelve,  a  most  important 
list,  are  carbon,  hydrogen,  oxygen,  nitrogen,  sulphur,  phosphorus,  chorine, 
sodium,  potassium,  calcium,  magnesium,  and  iron.  Besides  these  there 
are  others  less  universally  constant  in  biogen — namely,  silicon,  fluorine, 
iodine,  bromine,  aluminum,  manganese,  and  copper. 

Compounds. — So  far  in  describing  the  chemical  composition  of  pro- 
toplasm we  have  glanced  mostly  at  the  raw  materials  out  of  which 
protoplasm  is  evolved.  It  would  be  more  satisfactory  if,  using  these  as 
building-stones,  we  could  build  in  description  all  the  details  and  marvellous 
structures  which  we  know,  from  the  numberless  intricate  functions 
which  each  particle  of  protoplasm  includes.  But  this  cannot  as  yet  be 
done,  and  we  must  be  content  if  we  are  told  with  some  degree  of  certainty 
the  principal  features  of  the  protoplasmic  structure  and  the  functional 
relations  of  these  to  each  other  anrl  to  the  phenomena  of  life  in  general. 
(See  chapters  on  Food  and  Nutrition.) 

The  most  abundant  compound  present  in  primal  or  undifferentiated 
protoplasm,  and  in  most  of  the  animal  tissues  evolved  therefrom,  is  water. 
Life  is  characterized  principally  by  motion,  and  free  and  varied  motion 
depends  directly  on  the  lability,  the  ease  of  movement,  of  the  material. 
We  know  protoplasm  as  a  lifjuid  substance.  The  red-muscle  flesh  of  the 
ox  seems  solid  enough  to  the  unaided  eye,  but  carefully  examined  with 
a  microscope  or  with  reagents  every  component  particle  is  seen  to  be  a 
complicated  cell  filled  with  a  tliin  fluid,  lymph,  which  is  at  least  90  per 
cent,  water.  Even  the  bones  are  12  or  15  per  cent,  water,  and  the  tough 
and  solid-looking  ligaments  connecting  them,  77  per  cent.  Water  is  the 
universal  solvent  in  nature,  organic  as  well  as  inorganic.  As  Hoppe- 
Seyler  says,  "All  organisms  live  in  the  water,"  for  those  which  do  not  live 
literally  under  water  have  nearly  all  their  organs  composed  of  it  and 
surrounded  by  it,  and  continue  their  being  and  functioning  only  through 
its  means.  "Organisms  live  not  only  in  water,  but  in  flowing  water,"  the 
force  of  which  statement  will  be  fully  realized  later  when  the  rapidity  and 
ubiquity  of  the  blood-lymph  circulation  is  appreciated.     Practically  the 


PROTOPLASMIC  STRUCTURE 


27 


same  condition  is  brought  about  in  undifferentiated  protoplasm  by  its 
unceasing  movements,  through  the  growth  and  collapse  of  vacuoles  (de- 
fined on  page  4<S)  by  digestive  currents  through  the  animal,  and  in  other 
comparable  ways.  The  importance  of  water  as  a  food  and  for  other 
uses  in  the  tissues  is  readily  observed. 


Fig.  6 


A  protoplasmic  particle.  This  highly  diagrammatic  illustration  is  intended  to  suggest  the  com- 
plexity and  the  instability  of  the  unitary  j^article  of  protoplasm.  At  the  center,  perhaps,  is 
protein  vdth  cyanogen  (CN)  as  its  dore.  Closely  asso.  iated  are  a  fat  molecule  or  group  and 
a  carbohydrate  molecule  or  group.  Nearby  are  various  anabolic  materials  and  katabolic 
products  often  as  complex  as  the  fats,  etc.  Some  of  the  groups  about  are  partly  disintegrated. 
Water  and  oxygen  and  carbon  dioxide  and  salts  are  everywhere  about  and  enzymes  are  not 
wanting. 

The  second  important  class  of  the  constituents  of  protoplasm  is 
included  under  the  term  proteins.  These  are  the  most  abundant  con- 
stituents of  the  nucleus  and  the  cytoplasm.  In  the  former  they  contain 
phosphorus,  and  are  called  nucleins.  The  cellular  proteifls,  especially 
in  the  nucleus,  according  to  the  important  theory  advanced  by  Lilienfeld, 
Altman,  and  others,  are  all  combinations  in  various  proportions  of  one 
phosphorus-containing  substance,  nucleic  acid,  with  several  proteid-like 


28  PROTOPLASM  AXD  THE  CELL 

bodies  containincr  no  pliosphorus.  Accordiiioj  to  Miescher  this  nucleic 
acid  is  a  definite  chemical  body  with  the  formula  C^gH^yNgPgOgj,  the 
phosphorus  constituting  as  much  as  14  per  cent,  of  the  substance.  In 
combination  with  proteids  this  acid  forms  nucleins.  The  richer  these 
nucleins  are  in  nucleic  acid  the  more  acid  they  are,  and  the  richer  in 
phosphorus,  the  more  important  apparently  is  their  biological  role.  For 
example:  the  important  chromatin  of  the  nuclei  is  a  strongly  acid  sub- 
stance rich  in  phosphorus;  plastine,  the  basis  of  the  substance  of  the 
nucleolus  (Reinke),  has  less;  linin,  composing  the  linin  network  of  the 
nucleus,  still  less;  while  in  the  nucleo-albumin  of  the  cytoplasm  the  pro- 
portion of  nucleic  acid  is  small,  the  substance  scarcely  acid,  and  the 
quantity  of  phosphorus  only  1  per  cent.,  or  even  0.5  per  cent.  Lecithin 
and  cholesterin  seem  to  be  accessory  and  are  not  properly  a  part  of  the 
albuminous  molecule  (Delage).  Biochemists  seem  to  tend  toward 
the  supposition  that  nucleic  acid  is  the  basis  of  the  proteid  part  of  pro- 
toplasm, and  the  former  is  assuredly  the  predominant  portion  of  the 
protoplasmic  particle. 

Chemical  analysis  yields  various  formulae  for  different  sorts  of  proteid. 
Bunge  gives  these  four  as  typical,  but  calls  attention  to  the  divergence 
in  the  composition  of  proteid  matter  studied  under  the  best  of  conditions. 

FonMULA    OF    THE    PrOTEID    FROM 

Hen's  eggs C504H322N52O66S2 

Horse's  hemoglobin ^680^1098^2100241^2 

Dog's  hemoglobin CY^eHn-iNig^OjuSa 

Gourd  seed  (globulin) Ci92H48i^»'9o083S2 

From  such  a  list  fand  it  might  be  extended  almost  indefinitely)  it  is 
obvious  that,  however  much  the  idea  "proteid"  may  mean,  it  does  not 
identify  any  definite  substance  capable  of  being  represented,  as  yet  at 
least,  by  a  numerical  formula.  As  alrea<ly  has  been  noted,  this  fact  may 
be  due  in  small  part  to  the  impossibility  of  analyzing  protein  without 
first  changing  it  materially.  It  is,  however,  due  in  much  larger  part  and 
more  importantly  for  the  theory  of  biogen  to  a  consideration  of  a  different 
sort — namely,  that  proteid  has  no  constant  composition  to  be  numerically 
indicated.  We  are  not  dealing  here  solely  witli  mere  chemical  affinities 
between  chemical  elements  of  certain  valencies  and  invariable  reactions, 
such  as  those  which  take  place,  for  example,  when  sulphuric  acid  and 
ethyl  alcohol  are  heated  together  in  a  flask,  producing  ether: 

(C,H5)0H  +  HjSO^  =  (C,H5)S0,H  +  H,0 
(C',H5)S0,H  +  C2H5OH  =  (C2H6)20  +  H2SO, 

The  cliangcs  by  whifh  y)rotf)p!asmic  proteid  is  produced  and  changed 
and  reproduced  and  changed  again  in  plants  and  animals  are  practically 
based  on  this  sort  of  interchange.  There  is  present,  however,  in  metab- 
olic reactions  a  complexity  which  keeps  many  of  the  processes  and  their 
prmlucts  from  acenrate  description.  It  is  this  unimagined  intricacy  of 
chemical  reaetion  and  interaetjon  in  biogens  which  allows  the  occasional 


PROTOPLASMIC  STRUCTURE  29 

use  of  the  expression  "vital  force"  in  its  old  sense.  So  numerous  are  the 
reagents  and  so  numberless  their  reactions  in  certain  organs,  if  not  in 
every  one,  and  in  all  protoplasm,  that  it  seems  almost  as  if  there  must  be 
some  unifying  and  controlling  force,  some  principle  behind  and  beneath 
them  characteristic  of  life.  If  there  is  such  a  principle  (and  it  is  doubted 
by  some),  it  would  surely  be  as  much  inherent  in  the  proteids  of  organ- 
isms as  elsewhere.  Perhaps,  as  Pfluger  supposes,  it  would  be  there  alone, 
or,  as  is  more  likely,  in  an  atomic  structure  combined  of  proteids,  lecithin, 
carbohydrates,  the  inorganic  salts  of  several  metals,  etc.,  in  one  great 
ever-changing  adaptable  combination  well  meriting  the  title  of  the  vital 
molecule.  In  no  place,  however,  are  conjectures  more  out  of  place  than 
in  text-books  of  science.  We  must  hasten  to  declare,  therefore,  that 
about  the  actual  composition  and  spatial  arrangement  of  the  molecule 
of  proteid  we  know  nothing — and  we  could  certainly  not  know  less  about 
a  hypothetical  "vital  molecule,"  built  on  a  nucleoproteid  as  a  basis. 
That  air  of  pervading  mystery  for  which  the  term  "vital  force"  still 
stands  is  likely  to  continue  until  methods  of  chemical  analysis  new  and 
more  delicate  by  far  than  those  in  present  use  are  devised  and  put  in 
practice  on  living  protoplasm — the  enlightening  science,  not  yet  born,  of 
real  cytochemistry. 

The  definite  chemistry  of  proteids  has  not  advanced  sufficiently  to 
allow  of  any  sort  of  agreement  concerning  them  save  that  they  contain 
carbon,  hydrogen,  oxygen,  nitrogen,  and  sulphur,  there  being  disagree- 
ment even  as  to  the  universal  presence  of  phosphorus.  The  different 
proteids  or  albumins  (we  use  the  terms  as  synonymous)  have  not  been 
identified  with  sufficient  accuracy,  so  that  a  single  classification  is  in  use 
the  world  over.  Compare  in  this  respect  the  chemistry  of  the  saccharides 
or  of  the  glycerides  with  that  of  the  proteids,  and  it  is  obvious  how 
arbitrary  any  one  classification  of  the  latter  must  be.  The  following 
table  is  a  common  arrangement  of  the  albuminous  compounds  as  well  as 
of  the  others  which,  so  far  as  isolated,  combine  to  make  up  protoplasm. 
It  is  unlikely  that  all  of  these  are  contained  in  every  organism,  however 
low,  although  functional  representatives  of  them  are  probably  so  con- 
tained. These  substances  are  technically  known  as  the  proximate 
principles  of  the  animal  body.  The  more  promptly  and  permanently 
the  names,  relations,  and  functions  of  the  substances  in  this  table  become 
familiar  to  the  student,  the  easier  and  the  more  intelligible  to  him  will  be 
the  essential  composition  and  functions  of  animals. 

As  is  seen  in  the  following  table,  the  proteids  of  the  bodies  of  animals 
may  be  assumed  to  fall  under  six  general  classes:  albumins,  globulins, 
nucleoproteids,  chromoproteids,  glucoproteids,-  and  enzymes  (unorgan- 
ized "ferments,"  which  may  not  after  all  prove  to  be  proteids).  Into  the 
chemical  nature  and  differentiation  of  these,  as  into  their  varieties,  it  is 
not  our  province  to  go,  for  that  is  the  domain  of  another  science  than 
physiology — namely,  of  biochemistry.  All  that  we  desire  at  present  is 
to  understand  the  structure  and  composition  of  protoplasm  as  the  basis 
of  vital  phenomena. 


30 


PROTOPLASM  AXD   THE  CELL 


Constituents  of  ax  Animal  Body. 


Water  65  per  cent. 


SoUds 
•  and 
gases 


L  "Inorganic" 


f  Proteins. 


Albumins 


Globulins 


Nucleoproteid 


Chromoproteids 


L  Glucoproteids 


f  Organic .    .     ■{ 


Enzvmes 


f  Collagen :  gelatin. 

1  Elastin. 

I  Keratin. 

[  Neurokeratin. 

fOlein.  _ 

j  Palmitin. 

j  Stearin. 

[  Lecithin,  etc. 

f  Gl ycose :  dextrose. 

I  Saccharose :  lactose. 

{  Amyloses:  dextrin,  glj-cogen 

I  Cholesterin. 
I.  [  Animal  gum. 

f  XaCI.  Xa.,CO„  NaHCOg,  NaH^PO^,  NaSO^, 
I  CaHPO,,  CaCl,  CaCOj,  CaP-pg,  CaFl,, 
-j  KCl.  KjHPO^,  K,SO„  MgPO^,  MgCl^, 
I  NH,C1,  SiO,.  HCl,  Fe,  Mn,  O,  COj, 
L  H,  X,  XH3,  H,S,  CH,. 


Albuminoids 


Fats 


Carbo- 
hydrates 


r  Serum  albumin. 
\  Myoalbumin. 
f  Myosin, 
j  Serum  globulin, 
j  Myoglobulin. 
j  Fibrinogen, 
t  Globin. 
[  Crystallin. 

Xuclein. 
f  Hemoglobin. 
I  Hemocyanin. 
■{  Hemoerythin. 
I  Clilorocruorin. 
[  Hematin. 

Mucin,  etc. 
f  Ptyalin       )  Animal 

Amylopsin  J  diastase 

Pepsin. 

Rennin. 

Lipase. 
I  Trypsin. 

Erepsin. 
I  Kinase. 
I  Maltase. 

Saccharose. 

Lactase. 

Emulsin. 

Myrosin. 

Oxidases. 

Desamidase. 

TjTosinase. 

Urease, 
l_  Thrombin,  etc. 


The  cytoplasm  of  a  protoplasmic  cell  is,  according  to  Delage,  especially 
rich  in  nucleoproteids,  in  globulins,  in  lecithin,  in  cholesterin,  in  the 
chlorides  and  pho.sphates  of  potassium,  .sodium,  calcium,  and  •magnesium, 
and  in  iron.  The  first,  the  nucleoproteids,  containing  phosphorus,  and 
relatively  small  in  amount,  make  up  the  visible  structures  (fibrils,  gran- 
ules, etc.)  of  the  cytoplasm;  while  the  globulins,  containing  no  phos- 
phorus, form  the  amorj)hous  li(|uid  within  and  around  these  fibrils  or 
granules.  The  nucleoplasm  contains  chromatin  (which  probably  is 
h'cithin  and  cholesterin  in  combination  with  a  much  larger  proportion 
of  nuclein),  linin  (plastine  united  with  an  albuminous  substance)  making 
ti[)  the  finer  network  (see  page  22),  and  a  watery  substance  con- 
taining in  solution  various  proteid  bodies  precipitable  by  acids  and  by 
alcohol.    As  to  the  other  three  classes  of  albumins,  the  chromoproteids, 


PROTOPLASMIC  STRUCTURE  31 

gliicoproteids,  and  the  enzymes,  the  first  scarcely  exist  in  primal  or 
unditierentiated  protoplasm,  for  they  are  little  needed,  respiration  taking 
place  without  the  intermediation  of  hemoglobin — for  instance,  one  of 
the  chromoproteids.  Of  the  gliicoproteids,  the  chief  is  mucin.  The 
enzymes  are  numerous.  Their  functions  are  so  various  and  they  are 
so  small  in  amount  that  little  is  known  about  their  composition,  while 
to  describe  their  uses  would  be  out  of  place  here.  We  do  not  really  know 
that  they  are  proteids.  It  is  sufficient  at  this  point  if  it  becomes  clear  that 
every  organism  probably  contains  as  part  of  its  substance  these  six  classes 
of  proteids,  in  some  degree  and  proportion.  In  the  present  state  of  con- 
fusion concerning  the  relation  of  the  proteids  to  organic  function,  it  is  a 
great  satisfaction  to  be  aware  that  the  master  chemists,  such  as  Fischer, 
Bunge,  Hoppe-Seyler,  Hammarsten  and  Abderhalden,  find  as  much 
difficulty  in  forming  a  correct  idea  of  these  matters  in  their  minds  as 
do  those  who  look  to  their  work  and  to  their  opinions  for  information. 
Here  more  than  almost  anywhere  else  is  it  plain  that  physiology  is  far 
from  being  as  yet  a  science  anywhere  nearly  "exact" — so  continually 
does  the  "simple"  prove  infinitely  complex. 

One  other  general  consideration  concerning  the  proteids  should  be 
pointed  out — namely,  the  possibility  that  changes  much  more  extensive 
than  has  been  supposed  may  normally  take  place  in  the  chemical  com- 
ponents of  a  cell.  This  may  be  one  reason  why  constancy  of  analytic 
result  has  been  found  impossible — namely,  that  there  is  no  "constancy" 
in  the  analyzed  substances.  The  vital  interactions  in  protoplasm  are 
so  complicated  that  it  is  almost  impossible  to  say  how  far-reaching  cer- 
tain changes  may  be,  how  many  new  substances  are  formed,  how  often 
those  which  are  present  are  changed  back  and  forth  in  their  qualitative 
as  well  as  in  their  quantitative  compositions.  If  proteids  are  changed  to 
amino-acids  and  back  again  to  proteids  while  passing  quickly  through 
ths  thin  wall  of  the  intestine  it  is  difficult  to  estimate  the  making  and  the 
unmaking  which  a  mass  of  protoplasm  might  occasion,  given  sufficient 
time  and  space. 

The  third  sort  of  biogenic  components  or  proximate  principles  we  may 
consider  are  ih.e  fats.  The  fats  as  found  in  the  bodies  of  animals  occur  in 
three  pure  forms,  and  as  lecithin.  These  three  are  the  triglycerides  or 
ethers  of  oleic,  palmitic,  and  stearic  acids,  which  are  a  series  of  acids 
derived  from  monatomic  alcohols  by  the  process  of  oxidation.  (Choles- 
terin  is  a  monatomic  alcohol,  also,  found  in  every  cell:  formula,  C2eH^^O.) 
The  first  is  a  liquid  at  ordinary  room  temperature,  while  the  others  are 
solids,  melting  at  45°  C.  and  60°  C,  respectively.  They  thus  would  be 
more  or  less  solid  in  the  human  body  at  a  temperature  of  about  38°  C, 
were  they  not  held  in  solution  by  the  olein,  which  solidifies  only  at  five 
degrees  below  the  centigrade  zero.  There  are  two  ways  in  which  these 
triglycerides  and  their  compounds  are  parts  of  animals.  They  are 
deposited  in  masses  in  bone-marrow,  under  the  skin,  and  elsewhere  in 
the  bodies  of  many  animals.  In  minute  quantity  and  in  forms  as  \et 
hardly  known  they  enter,  it  seems  probable,  into  the  composition  of  the 


32  PROTOPLASM  AXD  THE  CELL 

(hvpothetical)  "vital"  particle.  Fat  has  not  been  found  in  the  nuclei  of 
cells.  In  the  former  case,  as  adipose  tissue,  the  droplets  of  the  tri- 
glycerides of  palmitic,  stearic,  and  oleic  acids  largely  take  the  place  of 
the  cytoplasm  of  connective-tissue  cells,  distending  the  cell  and  crowding 
the  nucleus  and  centrosomes  so  far  to  one  side  that  they  often  are  scarcely 
visible.  This  might  be  called  the  mechanical  occurrence  of  the  fats  as 
proximate  principles.  The  other  case  is  more  obscure,  and,  in  fact, 
uncertain.  It  is,  however,  probable  that  fat  in  some  form  and  amount 
enters  into  the  composition  of  all  protoplasm,  the  most  likely  form  being 
the  little-known  substance  lecithin.  This  is  a  very  complex  body  discov- 
ered by  Gobley  and  Diaconow,  best  classed  as  a  fatty  material,  but  made 
up  of  glycerin  in  combination  with  phosphoric  acid,  the  three  fatty  acids 
more  or  less,  and  the  cholin  discovered  by  Strecker.  Lecithin  is  most 
abundant  in  nerve-tissue,  but  seems  to  be  a  constituent  of  all  cells.  It  is 
especially  conspicuous  apart  from  the  nerves,  in  the  blood  corpuscles, 
muscles,  bile,  and  milk.  Of  the  function  of  lecithin  in  living  matter  we 
know  little  or  nothing,  but  that  it  takes  part  with  proteid  and  carbo- 
hydrate in  the  basal  vital  phenomena  there  is  little  doubt.  Some  have 
deemed  it  an  important  constituent  of  cell-walls,  supposing  that  it  deter- 
mines more  or  less  the  osmoses  in  and  out  of  the  cell.  Its  formula  is 
approximately  C^^Hg^XPOg,  which  has  interest  at  least  as  indicative  of 
the  elements  entering  into  its  composition. 

The  carhohydraies  are  the  fourth  class  of  protoplasmic  constituents  we 
need  discuss.  They  all  contain  hydrogen  and  oxygen  in  the  proportion 
in  which  these  elements  constitute  water  ftwo  to  one),  and  carbon  in 
varying  amounts.  Carbohydrates,  like  fats,  exist  in  the  nuclei  of  cells, 
if  at  all,  only  in  minute  amounts — too  small  to  have  been  found.  Our 
knowledge  of  the  chemistry  of  the  carbohydrates  in  its  completeness  is 
unlike  that  of  the  proteids,  but  their  biochemistry  is  biit  little  less  vague 
than  that  of  the  proteids.  Three  classes  of  carbohydrates  are  represented 
conspicuously  in  the  protoplasm  of  animals,  the  glycoses  (monosac- 
charides), the  saccliaroses  fdisaccharides),  and  the  amyloses  (polysac- 
charides). The  chief  glycose  of  protoplasm  is  dextrose,  which  exists  in 
animal  bodies  to  the  extent  of  0.1  per  cent.,  and  often  much  more. 
Another  name  for  dextrose  is  grape-sugar,  but  it  must  not  be  confused 
with  dextrin,  which  is  a  polysaccharide,  a  cleavage-product  of  the  hydra- 
tion of  starch.  The  formula  of  dextrose  is  CgHj20g,  and,  as  its  name 
implies,  it  rotates  the  plane  of  polarized  light,  as  seen  in  the  polarimeter, 
toward  the  right.  Dextrose  is  made  in  animal  bodies  from  the  hydrolysis 
of  starch,  of  the  disacfharides,  from  prf)t('i(l,  and  by  the  hydration  of 
glycogen,  the  form  of  starch  found  in  animal  protoplasm.  Its  important 
use  is  evidently  to  furnish  motive  energy  to  the  organism,  through  its 
oxidation  in  the  niiisflcs  and  other  organs.  The  most  abundant  sac- 
charose or  disaceliaride  found  in  am'mals  is  lactose,  CjjH^jO,,.  This  has 
not  l)e('n  isolated  from  any  tissue  of  the  body  save  that  of  the  mammary 
glands  during  lactation;  it  has  been  found  in  the  amniotic  fluid,  and 
.sometimes  in  the  urine  .soon  after  parturition  and  after  weaning.     By 


PROTOPLASMIC  STRUCTURE  33 

hydrolysis  it  is  split  into  (k-xtrose  and  galactose.  The  epithelial  proto- 
plasm of  the  mammary  glands  makes  lactose,  prol)ably  from  the  dextrose 
of  the  blood.  The  important  amylose  or  polysaccharide  of  protoplasm 
is  gli/cof/en,  the  animal  homologue  of  vegetable  starch.  Its  formula  is 
(CgHj^O-jn,  in  which  the  n  is  probably  six,  making  the  probable  formula 
of  glycogen  (CgHjp05)g,  while  that  of  vegetal;le  starch  is  most  likely 
(CqH^J.)^)^^^.  This  essential  and  interesting  substance  was  discovered 
by  Claude  Bernard  in  18.57,  and  was  called  glycogen  by  him  because  he 
found  it  to  be  the  immediate  source  of  the  tissue-sugar,  dextrose.  Glyco- 
gen is  made  from  proteids,  albuminoids,  and  carbohydrates  in  the  foofl 
of  the  animal.  It  probably  is  a  constituent  of  every  living  animal  cell, 
as  its  homologue,  starch,  is  of  every  vegetable  cell.  It  may  be  glycogen, 
or  some  body  very  similar,  which  joins  with  the  proteid  and  the 
"inorganic"  salts  to  constitute  the  huge,  labile,  and  changeful  particle 
characteristic  of  life. 

The  last  class  of  compounds  which  enter  regularly  into  protoplasm  are 
the  inorganic  salts.  These  are  crystalloids,  while  the  others,  except  water, 
are  generallv  either  fats  or  colloids  known  as  "hvdrosols."  Reference  to 
the  systematic  and  summarizing  table  of  proximate  principles  on  page 
30  will  show  just  which  of  the  inorganic  salts  are  universal  in  proto- 
plasm. Of  these,  the  chlorides  and  phosphates  of  calcium,  sodium,  and 
potassium  are  doubtless  the  most  important,  and  perhaps  are  the  only 
ones  universally  present  in  bioplasm,  unditl'erentiated  or  difl'erentiated. 
Their  source  to  the  animal  is  obviously  the  food  both  of  vegetable  and 
animal  origin,  for  all  plants  and  all  flesh  contain  these  salts.  One  of  the 
doubtful  and  difficult  matters  to  decide  in  physiology  at  present  concerns 
the  extent  of  the  usefulness  of  these  "inorganic"  salts  (the  name  is  obvi- 
ously misleading)  in  animal  protoplasm.  Through  physical  chemistry 
the  new  movement  in  biophysics  has  developed  rapidly  of  late,  and 
A.  P.  Mathews,  Loeb,  Nageli,  and  Hardy  have  opened  fields  involving 
ions  and  the  theory  of  electrolytic  dissociation  which  are  likely  to  define 
wherein  lies  the  great  importance  of  these  inorganic  salts.  Osmosis, 
hydrolysis,  and  coagulation  are  important  processes  in  animal  metabo- 
lism, yet  they  (and  possibly  muscular  contraction  and  nervous  conduction, 
etc.)  may  be  wholly  dependent  on  these  salts  for  their  accomplishment. 
It  is  on  little  difl'erentiated  protoplasm  that  many  of  these  researches 
have  been  made,  the  sort  that  makes  up  the  infusoria  and  other  unicells 
and  simpler  multicells;  and  the  investigations  have  shown  conclusively 
that  any  considerable  change  in  the  inorganic  salt  content  of  these  forms 
is  disastrous  to  the  animal.  In  the  "high"  forms  of  life  the  same  fact  is 
obvious  in  many  ways.  The  most  elaborate  means  are  employed  by  the 
most  highly  developed  animals  to  secure  the  uniformity  of  the  composition 
of  the  tissues  from  time  to  time,  and  especially  as  regards  the  crystalloids 
or  electrolytes  of  the  circulating,  but  all-pervading  fluids.  Thus,  whether 
ions  are  important  in  animal  metabolism  or  not  (and  few  today  doubt 
their  importance),  salines  can  be  proved  to  be  so  in  many  difterent 
respects  and  in  every  location  within  the  bodies  of  living  animals.  Nothing 
3 


34 


PROTOPLASM  AXD  THE  CELL 


has  done  more  to  render  superfluous  any  doctrine  of  a  "vital  force" 
than  the  development  of  our  knowledge  concerning  the  importance  of 
these  simple  chlorides,  phosphates,  carbonates,  and  sulphates  of  calcium, 
magnesium,  sodium,  and  potassium.  Just  as  surely  nothing  could  do 
more  to  indicate  the  extreme  complexity  of  vital  reactions  than  the  appar- 
ent need  of  including  them  as  well  as  proteid  and  carbohydrate  in  our 
list]of  the  components  of  the  huge  mass  of  molecules  characterizing  life. 


PROTOPLASMIC  FUNCTION. 


Fig.  7 


The  next  part  of  the  general  physiology  of  protoplasm  is  naturally  a 
description  of  its  basal  functions.    We  shall  examine  at  present,  then,  in 

the  merest  outline  only,  those  pro- 
cesses common  to  all  protoplasm  and 
try  to  learn  what  conditions  and 
uses  underlie  its  structural  nature. 
We  may  conveniently,  but  somewhat 
arbitrarily,  make  four  classes  of  the 
functions  of  protoplasm:  (1)  respi- 
ration, (2)  nutrition,  (3)  irritability, 
and  (4)  reproduction  and  growth. 
Within  these  four  types  of  organic 
activity  may  logically  be  included 
all  the  various  processes  character- 
istic of  the  tissues  of  animals. 

Respiration.— Respiration  is  a  func- 
tion common  to  all  that  lives,  to 
plants  as  well  as  to  animals.  It  con- 
sists essentially  of  the  taking  in  of 
oxygen  and  the  throwing  out  of 
the  products  of  the  oxidation  of  the 
tissues,  largely  carbon  dioxide  and 
water.  This  function  is  one  of  the 
most  fundamental  of  all  vital  pro- 
cesses, oxidation  being  the  most  uni- 
versal of  all  the  chemical  changes  in 
protoj)lasm.  This  union  of  oxygen 
with  the  tissues  of  animals  and  of 
plants  furnishes  the  basis  of  the  met- 
abolism which  is  their  life.  Proto- 
plasm respires  inevitably  and  always. 
In  the  minute  animals,  especially 
those  in  the  water,  ameba,  for  ex- 
ample the  change  takes  place  (h'rectly  between  the  protoplasm  and  the 
environment.  In  the  higher  animals,  however,  some  mechanism  is  neces- 
.sary  for  bringing  the  oxygen  (o  tin-  ])n)fo])lasiiiie  cells  in  the  interior  of  the 


Hydra.  A  fre^Ji-water  ."pefie.s  from  France, 
the  tentacles  fully  expanded.  On  tlie  right 
.•tide  of  the  trunk  in  seen  a  budding  daughter- 
hydra.      fDulxii?!.) 


PROTOPLASMIC  FUNCTION 


35 


body.  In  all  cases,  whether  in  infusorium  or  in  man,  the  basis  of  the 
process  is  an  attraction  of  the  living  matter  for  oxygen.  This  attraction 
is  apparently  inherent  in  the  protophism,  and  leads  to  the  same  general 
chemical  chano-es  which  oxidation  would  lead  to  outside  of  an  organism. 
Here  as  elsewhere  it  is  only  because  of  the  unparalleled  complexity  of  the 
chemical  reactions  that  the  process  is  not  explainable  in  all  its  details. 
Of  all  the  many  interchanges  between  protoplasm  and  its  environment, 
this  interchange  of  oxvg-en  and  carbon  dioxide  is  bv  far  the  most  uni- 
versal,  and  as  a  source  of  energy  the  most  important. 

Nutrition. — The  nutrition  of  a  mass  of  protoplasm  is  the  sum  of  those 
chemical  changes  within  it  by  which  it  is  supplied  with  the  means  of 
liberatino;  energv  and  of  building  tissue.  These  changes  are  almost 
infinitely  complex,  and  are  summarized  under  the  name  metabolism. 


The  nutrition  triangle.      Anaboiism  versus  katabolism. 


Metabolism  has  two  phases:  One  of  them,  the  upbuilding  process,  is 
called  anaboiism,  from  the  Greek  ana,  up.  The  other  phase  is  katab- 
olism, or  the  downtearing  of  organic  tissues,  from  the  Greek  hata, 
down.  These  words  are  of  constant  and  ever-increasing  use  in  physiology, 
for  they  indicate  the  chemism  as  the  basis  of  the  material  life  of  all  animals 
and  plants. 

Nutrition  is  divided  into  several  parts — namely,  digestion,  absorption, 
assimilation,  and  excretion.  In  highly  developed  animals,  and  in  many 
of  the  simpler,  there  are,  besides  these  four,  other  nutritional  processes, 
such  as  prehension,  mastication,  insalivation,  deglutition,  circulation, 
absorptive  selection,  urination,  and  defecation.  The  last  two  are  strictly 
processes  of  nutrition  only  in  a  broad  sense  of  the  term.  At  the  same 
time  they  are  indispensable  parts  logically  of  the  different  processes  of 
nutrition,  and    there  are   therefore  treated   in   that  connection.     The 


38 


PROTOPLASM  AND  THE  CELL 


most  fundamental   processes   of  all   these   are  digestion,   assimilation, 
and  excretion. 

Digestion  is  the  organic  function  of  preparing  food  for  assimilation 
to  the  tissues  or  for  the  liberation  of  its  energy  in  the  tissues  (these 
being  the  two  uses  of  food).  The  important  fact  concerning  this  process 
is  that  digestion  in  its  essentials  is  apparently  the  same  in  all  animals, 
however  simple  or  complex.  Protoplasm  is  in  the  most  general  sense  a 
particular  sort  of  substance  in  all  animals,  and  the  foods  of  all  animals 
have  certain  characters  in  common.  The  means,  therefore,  by  which  the 
food  is  changed  into  protoplasm  would  be  naturally  only  one  general 
process.  Thus  we  find  the  digestive  juices  in  a  simple  mollusk  to  be 
practically  of  the  same  composition  as  those  of  man.  When  an  ameba 
(see  page  49)  surrounds  a  minute  particle  of  food  and  secretes  from  its 
homogeneous  substance  a  vacuole  of  liquid,  this  liquid  digests  the  food- 
particle  in  all  probability  quite  as  a  like  fluid  would  digest  a  like  food- 
particle  in  the  human  stomach. 

Fig.   9 


Eugleiia  viiidis,  Ehr.:  a  and  h,  the  freely  active  condition,  b  being  one  phase  of  its  peculiar 
contortions;   c,  d,  and  e,  encysted  and  dividing  conditions.      (Stein.) 

Assimilation  is  the  process  by  which  nutritive  materials  supplied  as 
food,  having  been  digested,  are  incorporated  into  the  substance  of  the 
animal's  })n)toj)lasm.  Here  the  new  materials  may  be  katabolized  and 
furnish  energy  (heat,  power  of  movement,  electricity,  light,  etc.),  or 
they  may  become  an  addition  to  the  protoplasm  of  the  animal  either  to 
promote  growth  fas  in  early  life)  or  merely  to  replace  the  tissue  lost  in  the 
inevitable  wear  and  tear  of  use.  It  is  in  this  ])r()cess  of  assimilation  that 
is  found  the  greatest  difficulties  in  explaining  the  changes  which  have 
to  be  made  before  a  food  can  become  bioplasm.  Little  is  actually 
known  about  the  ehemir-al  changes  by  which  the  digested  food  materials 
are  elaljorated  into  tissue-jM-otopIasm.  The  reason  for  this  is  obvious 
when  it  is  considered  that  the  building  up  is  a  molecular  process,  deep 
in  the  hidden  tissues  of  the  body,  and  that  it  innnediately  stops  when 
analysis  or  direct  ob.servation  is  made  possible.  In  other  words,  seem- 
ingly paradoxical,  the  anabolism  of  protoplasm  occurs  only  in  living 
matter,  and  the  process  cannot  be  observed,  because  in  order  to  do  so  the 
matter  must  be  killed. 


PROTOPLASMIC  FUNCTION 


37 


Fig.  10 


i/\\l/H///j 


Excretion. — Excretion  is  the  third  of  the  essential  processes  involved 
in  nutrition.  It  is  made  necessary  by  the  four  circumstances  that  most 
food  contains  an  indigestible  element;  that  the  parts  of  an  organism 
select  what  they  wish  and  reject  the  rest';  that  some  digestible  food 
escapes  digestion,  for  one  reason  or  another;  and,  most  important  of  all 
theoretically,  that  the  katabolism  of 
the  tissues  produces  much  material 
not  only  lacking  in  any  value  to  ani- 
mals, but  actually  poisonous  to  them 
if  retained.  Thus  we  see  that  the 
removal  of  waste  products  is  an  indis- 
pensable process,  not  only  practically 
but  theoretically,  for  the  products  of 
katabolism  are  largely  either  poisonous 
in  themselves  or  the  natural  food  of 
harmful  bacteria  which  in  turn  produce 
toxins  that  are  often  of  a  deadly  nature. 

Irritability. — Irritability  is  the  term 
which  is  used  to  designate  all  the 
functions  or  vital  manifestations  of  pro- 
toplasm not  included  in  nutrition. 

Irritability  may  be  defined,  perhaps 
too  tersely,  as  the  reactibility  of  pro- 
toplasm to  stimulation,  a  definition 
indicative  of  the  general  meaning  of 
the  term.  Indeed,  as  has  already 
been  indicated,  irritability  is  not  con- 
fined to  animals  or  even  to  organisms, 
for  gunpowder,  as  Thompson  says, 
acts  vigorously  to  the  stimulation  of  a 
spark,  and  similar  examples  are,  of 
course,  numerous.  Irritability  is  then 
the  most  general  property  of  proto- 
plasm. If  respiration,  nutrition,  and 
reproduction  are  discussed  under  dif- 
ferent heads,  it  is  for  convenience  and 
because  of  their  separate  importance, 
rather  than  because  these  phenomena 
are  outside  the  manifestations  of  irri- 
tability. Thus,  respiration  is  a  sys- 
tematized reaction  to  the  stimulation 
of  an  excess  of  carbon  dioxide;  nutrition,  a  reaction  to  a  lack  of  oxygen 
and  of  food,  and  reproduction,  a  reaction  to  complex  sexual  strains 
and  processes. 

Move:mext. — ^Movement  is  the  most  conspicuous  of  the  animal 
reactions  to  stimulation.  If  a  speck  in  a  distant  landscape  or  in  the 
field  of  a  microscope  moves,  the  presumption  is  almost  instinctive  that 


Grovia   oviformis   feeding.      (Dubois.) 


38 


PROTOPLASM  AND  THE  CELL 


it  is  alive.  So  strong  is  the  instinctive  feeling  in  all  animals  that  squirrels 
will  sometimes  run  over  a  motionless  figure  as  over  a  fallen  log.  Motion, 
though  unsatisfactory  to  define  either  by  common  sense  or  by  meta- 
physics, is  a  quality  of  protoplasm  inherent  in  the  matter  of  which  it  is 
made.  Probably  movement  inheres  as  characteristic  in  the  structure 
of  the  so-called  biomolecule.  The  most  important  kinds  of  movement 
are  produced  by  the  active  contraction  of  the  protoplasm.  These  are 
three  in  number — namely,  streaming,  ciliary,  and  muscular.  The  first 
occurs  in  undifferentiated  bioplasm  and  in  the  leukocytes,  the  second  in 


Fig.   11 


Fig.   12 


'.'  S^ 


Paramecium  caudatum,  Ehr.     X  250.      (Conn.) 


A  cell  of   ciliated    epithelium   from  a   mollusk. 
(Engelmann.) 


cells  which  have  evo'ved  into  a 
special  sort  of  epithelium,  and  the 
last  in  highly  specialized  cells 
adapted  to  this  one  function  of 
causing  motion.  All  of  these  are 
obviously  dependent  on  the  fluidity 
of  the  living  matter. 

The  streaming  movements  of  protoplasm  are  of  much  interest,  and  in 
a  sense  are  the  type  of  which  the  other  two  are  only  variations.  These 
movements  may  be  seen  in  the  ame})a  (Fig.  1),  aj)]>arently  only  a  speck 
of  gelatinous  licpiid,  comparatively  at  rest  at  first,  somewhere  on  the 
slide  of  the  microscope.  Soon  a  slight  bulging  occurs  at  the  edge  of 
the  cytoplasm,  and  this  gradually  increases  and  becomes  a  projection, 
extending  outward  as  much  as  the  former  diameter  of  the  cell,  or  even 
much  farther.  If  the  animal  be  bent  on  progression  (for  example,  to 
escape  frf)m  too  bright  a  lightj,  tlie  whole  body  of  protoplasm  slowly 


PROTOPLASMIC  FUXCTJOX  39 

streams,  or  flows,  into  this  pseudopod,  as  it  is  called,  the  ameba,  when 
this  is  done,  hav  ntr  travelled  its  own  diameter. 

Often  when  one  looks  at  the  animal  on  the  slide  of  a  microscope  there 
is  no  such  progression  in  process,  and  several  pseud opodia  may  be 
extended  in  several  directions  at  the  same  time,  all  different  in  shape  and 
size,  save  by  accident,  but  all  formed  by  this  same  peculiar  streaming, 
rolling  form  of  motion  characteristic  of  the  liv  ng  substance.  The  strik- 
ing impression  which  it  gives  is  that  the  whole  mass  all  through  is  equally 
alive  and  ec|ually  active  and  helpful  in  the  general  heaving  and  flowing 
movements  of  the  pseudopodia  s  owly  back  and  forth.  Sometimes  the 
movement  is  aimless,  sometimes  after  food,  but  it  seems  almost  as  if  the 
motion  were  inherent  in  the  substance,  pervading  it  thoroughly  in  every 
part.  That  is  the  so-ca  led  ameboid  movement,  difficult  to  describe,  but 
fascinating  and  instructive  when  seen  under  the  microscope.  This  is  the 
basal,  actively  vital  movement  of  the  almost  unflift'erentiated  protoplasm, 
automatic  and,  in  a  sense,  inseparable  from  the  nature  of  the  living  sub- 
stance save  at  special  periods  when  certain  animals  may  become  encap- 
sulated and  rest.  The  physical  principles  on  which  these  movements 
depend  are  in  doubt,  but  the  principle  of  surface-tension  in  liquids  is 
probably  the  most  important  of  them.    Kiihne,  in  1864,  showed  that  the 

Fig.   13 
Diagram  of  a  row  of  cilia  to  show  the  rhythmic  nature  of  the  contraction.      (Verworn.) 

extension  of  a  pseudopod  represents  a  decrease  of  the  surface-tension  at 
the  point  where  it  projects.  He  supposed  this  decrease  to  be  caused  by 
the  absorption  at  that  spot  of  some  of  the  surrounding  oxvgen,  the 
cohesion  of  the  biomolecular  atoms  being  lessened  by  the  admission  of 
these  atoms  of  oxygen  into  the  living  molecule.  The  retraction  of  the 
pseudopod  is  accounted  for  by  supposing  that  the  absorption  of  the 
oxygen  at  that  point  causes  an  increase  of  surface-tension  which  retracts 
the  pseudopod.  ^>rworn's  further  supposition  is  that  the  mass  of  mole- 
cules thus  more  or  less  exhausted  of  their  energy  is  restored  to  the  vigor 
necessary  for  activity  by  metabolic  interchange  with  the  nucleus  of  the 
cell.  Quincke  showed,  however,  that  oil  drops  in  an  alkaline  liquid  have 
an  action  similar,  under  certain  conditions,  to  that  of  drops  of  living 
protoplasm.  Biitschli's  researches  already  mentioned  are  conclusive 
that  some  at  least  of  the  phenomena  of  protoplasm  may  be  imitated  with 
inorganic  materials. 

The  second  class  of  movements  in  protoplasm  due  to  its  active  con- 
traction and  passive  relaxation  consists  of  those  called  ciliarv.  A  cilium 
is  a  thread-like  projection  from  the  protoplasm  of  certain  cells,  while  a 
flagellum  is  an  enlarged  and  somewhat  elaborated  cilium.  Cilia  appear 
to  be  present  in  nearly  all  animals  above  the  very  lowest,  either  on  the 


40  PROTOPLASM  AXD  THE  CELL 

surface  of  layers  of  ciliated  epithelium  (as  in  the  bronchi  and  Fallopian 
tubes),  or  as  flagella  attached  to  the  spermatazoa,  or  about  such  uni- 
cellular animals  as  paramecium.  In  the  former  case  the  function  of  the 
cilia  is  to  move  along  light  substances  which  adhere  to  them  (for  example, 
dust  particles  in  case  of  the  bronchi,  ova  in  the  Fallopian  tubes).  Fla- 
gella move  the  cell  of  which  they  are  a  part  through  its  liquid  environ- 
ment, or  else,  as  in  hydra,  move  masses  of  licjuid  within  the  animal. 
The  cilia  are  a  somewhat  differentiated  part  of  the  protoplasm  proper, 
and  in  cases  where  a  cell-wall  exists  they  extend  through  pores  in  the 
latter.  The  motion  of  cilia  consists  alternately  in  a  forcible  contractile 
erection  and  a  slower,  more  or  less  passive  relaxing  movement.  The 
position  of  the  cilium  in  the  former  case  is  perpendicular  to  the  general 
surface  of  the  cell,  and  in  the  latter  more  or  less  parallel  to  it.  It  is  largely 
through  the  difference  in  the  velocity  of  these  two  phases  of  motion  that 
their  motor  function  is  possible.  The  movement  of  a  surface  of  the  cilia 
shows  a  perfect  rhythm,  best  described  by  the  partly  schematic  figure 
(Verworn).  In  many  cases  the  movements  of  the  cilia,  and  of  the  flagella 
especially,  are  complicated  combinations  of  spiral,  funnel-shaped,  whip- 
movements  and  of  others  too  complex  to  be  indicated.  The  principle 
of  action  is  in  all  cases  similar — namely,  according  to  Verworn,  that  "a 
contractile  side  (of  a  cilium)  contracts  from  the  cell-body  outward,  and 
thereby  the  opposite  side  is  extended;  in  the  phase  of  expansion  (or 
relaxation)  the  latter  by  its  elasticity  brings  the  cilium  back  into  the 
position  of  rest.  According  to  the  relative  positions  of  the  contractile  and 
the  passively  extended  substances,  there  results  a  movement  in  a  plane 
or  a  more  complicated  form."  The  mechanism  by  which  the  rhythm 
of  movement  on  a  surface  of  ciliated  epithelium  is  kept  up  with  such 
perfect  regularity  and  adaptation  to  the  needs  is  not  understood.  The 
existence  of  a  nervous  coordinating  apparatus  has  not  been  proved,  so 
that  it  depends  on  impulses  passing,  in  manner  and  route  unknown, 
through  the  protoplasm  itself,  and  from  cell  to  cell  indefinitely.  Such 
subjects  as  this,  the  typical  movements  of  the  basal  protoplasms,  which 
are  almost  impossible  of  being  understood  by  mere  flescription,  at  once 
illustrate  and  prove  the  importance  of  actual  laboratory  work  in  elemen- 
tary biology  as  a  part  of  every  course  in  physiology. 

The  third  variety  of  active  contraction-relaxation  movement  exhibited 
by  protoplasm  that  may  be  mentioned  is  muscular  movement.  The 
needs  of  the  evolving  animal  world  rapidly  became  complex  at  an  early 
period,  and  demanded  evidently  a  closer,  stronger,  and  more  adaptable 
means  of  motion  than  was  possible  from  any  sort  of  bioplasm  then 
existing.  Thus  (so  runs  the  teleological  theory  of  evolution)  muscle  was 
made  to  develop,  with  its  com})lex  and  extraordinary  functions.  In 
general  terms  this  function  is  always  either  to  (h-aw  closer  together  two 
parts  of  an  organism  or  else  to  diminish  the  caliber  of  a  tube  or  of  a  hollow 
vi.scus.  Anifjng  the  lower  and  simpler  animals  various  transition-stages 
between  epitlidinni  and  muscle  (•ells  mav  be  found.  Sometimes,  for 
example,  one  sees  the  upper  j)art  of  an  epitlielial  cell  developed  into  a 


PROTOPLASMIC  FUNCTION 


41 


structure  which  is  essentially  a  smooth  muscle  cell.  Within  this  minute 
organ  very  fine  contractile  fibers  are  to  be  found,  known  as  mvoids,  and 
it  is  this  elementary  thread-like  mass  of  protoplasm,  capable  of  short- 
ening, which  seems  to  be  characteristic  of  all  the  varied  sorts  of  muscle 
described  in  a  separate  chapter  below. 

Besides  movements  due  to  active  contraction  and  the  passive  relax- 
ation of  protoplasm,  there  are  others  of  much  less  frecjuent  occurrence, 


Fig.    14 


Fig.    15 


Eijithelial  cells  from  the  human  trachea, 
ciliated  and  goblet  cells:  a,^  a,-  and  a',  various 
stages  in  the  development  of  the  ciliated  cells; 
b  and  6',  goblet  cells;  d,  the  upper  ends  of 
two  developed  goblet  cells.  (Behrens,  Kossel, 
and  Schiefferdecker.) 

and  therefore  of  less  importance. 
One  of  these  is  caused  bv  changes 
in  the  specifie  gravity,  the  animal 
cell  being  made  lighter  by  the 
secretion  of  a  bubble  of  carbon 
dioxide,  and  then  at  another 
time  heavier  than  water  by  the 
expulsion  of  this  bubble  of  gas. 
Again,  certain  forms  progress  by 
the  continuous  secretion  of  a 
viscid  substance  from  the  end  of 
the  body  which  is  in  contact  with 
the  surface  along  which  it  moves. 
Secretiox. — Another  manifes- 
tation of  the  irritability  of  proto- 
plasm is  to  be  seen  in  the  general 
function  of  secretion.  In  some 
form  or  other  this  is  a  universal 
activity  in  protoplasm.  Secretion 
which  protoplasm  produces  within 


Some  different  types  of  epithelial  cells:  a, 
ciliated  epithelium;  b,  cylindrical,  seen  in  profile; 
d,  the  same  seen  on  the  end;  /,  cells  with  flagellae 
and  "collarettes;"  g,  flagellate  cells;  h,  digestive 
cells  w-ith  ameboid  projections  (as  in  hydra);  i, 
stratified  epithelium;  k,  external  epithelium  of  a 
marine  planarian  with  pigment-cells,  epithelial 
cells,  and  gland-cells  beneath.      (Dubois.) 

may  be  said   to  be  the  process  by 
itself  bv  its  own  activitv  some  sub- 


42 


PROTOPLASM  AXD   THE  CELL 


stance — ^gaseous,  Ikiukl,  or  solkl.  It  is  obvious  that  in  any  process  a 
definition  as  general  as  this  may  be  both  widespread  and  various  in  its 
details.  These  details  will  be  described  in  another  chapter.  Here  it 
is  necessary  only  to  note  that  the  process,  however  various  in  man, 
does  not  diti'er  in  its  essentials  from  the  process  in  the  lower  order  of 
animals. 

The  Production  of  Energy. — Still  another  manifestation  of  irri- 
tabilitv  in  protoplasm  is  the  production  of  energy.  Energy  is  that  which 
mav  give  rise  to  change  in  the  properties  of  matter  or  in  its  location. 
Work  in  the  gross,  mechanical  sense,  involving  visible  space,  need  not, 
however,  be  concerned  in  the  biological  varieties  of  expenditure  of  energy. 
We  have  already  discussed  one  variety,  the  kinetic  sort,  as  employed  in 
some  of  the  movements  of  protoplasm.  Besides  the  power  to  move, 
there  are  resident  in  protoplasm  the  power  to  produce  (2)  chemism,  (3) 
heat,  (4)  electricity,  (o)  light,  while  it  is  an  undetermined  matter  at 
present  whether  f6)  inhibition  is  considered  another  manifestation  of 
energy.  These  are  all  expentlitures  on  the  part  of  protoplasm,  different 
modes  of  reaction  to  a  stimulus. 


Fig.    16 


A  transverse  section  in  the  ventral  light -organ  of  pyrophorus:  m,  m,  muscles  on  the  edges  of 
the  Vjlood-sinus  whose  opening  is  at  S.  The  influx  of  blood  into  the  mass  of  cells,  under  pressure 
from  the  muscles,  gives  rise  to  the  light.     (Dubois.) 

Conductivity. — Conductivity  is  yet  another  important  manifesta- 
tion of  irritability.  This  is  a  universal  property  of  living  matter,  although 
one  reduced  to  its  logical  minimum  in  some  of  the  tissues — enamel,  for 
example.  But  this  is  .scarcely  alive  any  more  than  is  a  clam-shell  or  the 
quartz  .sheath  of  the  caddis-fly  lava  of  our  acjuaria.  At  the  same  time, 
as  we  have  suggested,  even  enamel  is  technically  a  tissue  made  of  "pro- 
toplasm." The  power  which  protoplasm  has  of  conducting  through  its 
substance  any  adecjuate  stimulus  may  be  seen  practically  in  any  of  the 
common  unicells — for  example,  paruinccian,  ameba,  or  even  in  plants, 
.such  as  the  leaf  of  the  famous  jjjaiit  Dioiica  (Venus'  flytrap).  If  any 
part  of  one  of  these  animals  or  leaves  is  touched,  it  is  obvious  that  the 
whole  organism  is  immediately  afi'ected — in  other  words,  the  stimulus 
is  conductefl  throughout  the  protoplasm.  This  is  about  all  that  can  be 
.said  on  this  sMl)jcft  in  the  way  of  explanation,  for  the  means  of  communi- 
cation through  the  f)roto[)ljism  from  niolcculc  to  molecule  is  al)solutely 
unknown.    So  important,  however,  is  this  fuiutioii  of  conveyance  of  a 


PROTOPLASMIC  FUNCTION 


43 


stimulus  from  one  part  of  an  animal  to  another  that  a  special  tissue, 
nerve,  has  evolved  so  that  it  may  be  done  more  promptly  and  more 
accurately.  The  nervous  system,  then,  aside  from  the  important  sup- 
posed relation  to  spontaneity  and  consciousness,  is  only  an  immensely 
complicated  series  of  protoplasmic  paths  through  the  various  parts, 
large  and  small,  of  the  body,  and  connecting  by  means  of  the  sense  organs 
the  individual  animal  with  its  environment.  This  main  function  of 
conduction  is  discussed  in  the  chapter  on  the  Nervous  System. 

Taxes. — This  term  is  used  to  indicate  several  sorts  of  reactions  to  the 
stimulation  of  protoplasm.  It  has  largely  replaced  the  older  word 
tropism.  The  term  is  from  the  Greek  taxeo,  to  arrange,  and  in  phy- 
siology indicates  a  tendency  which  various  animals  and  plants  exhibit  of 
arranging  or  coordinating  themselves  in  various  ways  to  different  sorts 
of  stimuli  or  conditions  in  their 

environments.       Especially  does  fig.  17 

the  word  taxis  indicate  the  attrac- 
tion towarfl  the  places  where 
these  conditions  or  stimuli  are, 
or  away  from  them.  The  most 
important  of  the  taxes,  only  re- 
cently investigated,  and  then  with 
not  very  important  results,  are 
chemotaxis,  attraction  toward 
certain  substances;  thermotaxis, 
toward  heat;  phototaxis,  toward 
light;  electrotaxis,  toward  elec- 
tricity; and  barotaxis,  toward 
pressure,  including  thigmotaxis, 
rheotaxis,  and  geotaxis.  Though 
they  are  interesting,  and  possibly 
of  some  importance  in  explaining  the  behavior  of  animals,  space  does 
not  allow  a  further  discussion  of  these  reactions  in  this  place. 

Consciousness  has  such  a  close  relation  to  the  living  substance  that 
it  may  be  mentioned  here,  for  convenience,  without  in  any  sense  giving 
it  classification  as  a  manifestation  of  the  irritability  of  protoplasm. 
AMiatever  consciousness  or  mental  activity  may  be  (and  it  cannot  be 
defined  except  as  experience),  it  has  a  relation  to  protoplasm  such  that, 
so  far  as  we  actually  know,  it  does  not  exist  apart  from  bioplasm.  Xo  one 
at  present  considers  it  a  function  of  protoplasm  or  a  product  of  proto- 
plasmic life.  Thought  is  no  longer  said  to  be  "  the  secretion  of  the  brain, 
as  urine  is  of  the  kidney,"  but  it  is  in  some  quite  unknown  way  related 
to  the  irritability  of  protoplasm,  and  is  at  once  master  and  servant  of  the 
living  substance  of  animals  and  an  accompaniment  of  its  life.  The 
chief  usefulness  of  consciousness  (if  for  the  sake  of  system  Ave  must  find 
a  biological  "function"  for  it)  is  probably  resident  chiefly  in  memory. 
It  is  the  means  by  which  experiences  are  acquired  for  preservation  in 
memory  to  be  of  further  use  to  the  individual.     (See  Chapter  XII.) 


A  diagrammatic  section  through  the  photogenic 
organ  of  a  Hghtning-bug  (Pyrophorus  noctilucus): 
C,  cuticle;  h,  hypodermis;  O,  luminous  organ;  S, 
blood-sinus  of  the  organ;  a,  adipose  body;  tr, 
tracheoe;  m,  muscles;  n,  nerves.      (Dubois.) 


44 


PROTOPLASM  AND  THE  CELL 


ReproductionT^and  Growth. — The  fourth  and  last  of  the  classes  of 
functions  of  protoplasm  deals  with  the  means  by  which  the  races  of 
animals  are  continued,  as  the  three  other  classes  discuss  some  of  the 
protoplasmic  fimctions  as  means  of  continuance  of  the  individual  organ- 
ism. Chapter  XIII  is  devoted  to  the  physiology  of  mammalian  and 
especiallv  of  human  reproduction.  In  this  connection,  therefore,  we 
shall  confine  ourselves  to  the  underlying  principles  of  cell-division  and 
of  cell-growth,  and  of  what  might  almost  be  called  protoplasmic  repro- 
duction. 

Fig.  18 


^ 


^■^'V 


f^1 


Diagram  of  amitotic  cell-division,  showing  an  Ameba  polyijodia  becoming  two. 
{V.  E.  Schulze.) 


AiiiTOSiS. — Amitosis  is  direct  cell-division  or  tlirect  nuclear  division. 
This  mode  of  division  has  been  seen  to  occur  in  leukocytes  and  in  epithe- 
lial cells,  especially  those  of  arthropods.  It  occurs  also  in  the  protista, 
and  in  other  forms.  The  process  of  amitosis  is,  so  far  as  the  micro- 
scope shows,  very  simple;  none  of  the  complex,  minute  organs  (spindles, 
radiations,  asters,  chromosomes,  etc.),  soon  to  be  described,  are  appar- 
ently employed  in  this  process.  In  amitosis  the  nucleus  simply  flows 
apart,  and  this  is  folKnvcd  by  a  similar  active  division  of  the  cytoplasm, 
the  whole  cell  thus  being  made  two.  First,  the  nucleus  elongates,  and  then 
by  active  protoplasmic  streaming  one-half  separates  gradually  from  the 
other  in  the  cytoplasm.  ^Meanwhile,  the  latter  has  liegun  the  same  pro- 
cess and  slowly  becomes  constricted  between  the  separated  nuclei.  This 
constriction    becomes   gradiKilly    more    slender    and    lengthened,    until 


PROTOPLASMIC  FUNCTION  45 

perhaps  only  a  thread  connects  the  two  new  daughter-cells.  Finally, 
this  is  cut  quite  through  and  the  process  is  complete,  rccjuiring  in  ameba, 
where  it  may  in  rare  instances  be  observed,  about  three  hours.  Some- 
times the  course  of  the  division  is  interrupted  and  much  disturbed,  as 
it  were,  by  confusion  or  disagreement  among  different  parts  of  the 
cytoplasm,  and  there  may  be  long  delays  seemingly  at  any  stage  of  the 
process,  but  especially  during  its  later  stages.  From  this  or  some  other 
cauge,  the  nucleus  often  breaks  up  into  many  daughter-nuclei,  as,  for 
example,  in  the  giant-cells,  which  may  break  up  then  into  several  new 
cells  containing  the  nuclei  near  their  peripheries  (Arnold). 

Mitosis. — jMitosis,  karyokinesis,  indirect  nuclear  or  cell-division,  or 
nuclear  segmentation,  is  the  complicated  process  by  which  the  great 
multitude  of  cells  divide,  for  amitosis  is  decidedly  the  exception  in  the 
animal  world.  The  simple  purpose  of  this  marvellously  complex  process 
is  to  divide  equally  the  essential  parts  of  the  nucleus  and  of  the  cyto- 
plasm of  the  mother-cell  among  the  two  daughter-cells.  As  will  be 
recalled  (see  page  ^3),  a  typical  cell-nucleus  has,  besides  its  linin  retic- 
ulum and  nuclear  sap  or  enchylema,  numerous  masses  of  nuclein  irregu- 
lar in  shape  (but  usually  elongated),  of  chromatin  termed  chromosomes, 
and  one  or  more  nucleoli.  The  cytoplasm,  besides  its  foam-like  probable 
reticulum  and  enchylema,  has  in  it  (at  least  during  its  periods  of  repro- 
ductive activity  and  perhaps  at  all  times)  a  small  body  called  the  attrac- 
tion-sphere, at  the  centre  of  which  is  a  minute  round  body  known  as  the 
ccntrosome.  Yatsu  has  shown  this  to  be  an  organ  independent  structu- 
rally of  both  nucleus  and  cytoplasm,  although  derived  from  the  latter,  a 
third  constituent  of  the  cell;  and  it  is  thus  that  we  have  classed  it  above. 
Its  exact  status  is  still  in  doubt. 

The  process  of  mitosis,  remarkably  constant  in  the  thousands  of 
animal  species  and  cells,  may  be  seen  graphically  represented  in  the 
diagrammatic  Fig.  19,  taken  from  Flemming.  The  aftraction-sphere 
is,  in  the  resting  cell  not  about  to  divide,  either  in  tlie  nucleus  or 
close  to  the  nucleus  in  the  cytoplasm,  and  inconspicuous  probably  out- 
side and  at  one  end  of  the  latter.  When  the  process  of  mitosis  is  about 
to  begin  the  centrosomes  separate  within  the  attraction-sphere  and  soon 
divide  the  latter  into  two  parts,  connected  by  fibrils.  Each  becomes  the 
center  of  numerous  rays  which  extend  outward  in  all  directions,  con- 
spicuously througii  the  cytoplasm,  the  whole  of  each  being  called  an 
aster.  ^leanwhile  the  masses  of  chromatin  of  the  nucleus  have  arranged 
themselves  into  lines  or  threads  (A)  (hence  the  name  mitosis,  given  by 
Flemming),  or  perhaps  into  one  thread,  coiled  on  itself  within  the 
nucleus.  This  soon  breaks  up  into  particles  called  chromosomes.  The 
number  of  these  chromosomes  is  constant  for  one  animal  species — 
twenty-four  in  the  mouse,  salamander,  and  trout;  sixteen  in  the  guinea- 
pig,  ox,  and  man;  sometimes  they  are  only  four,  or  even  two.  O. 
Hertwig  is  of  the  opinion  that  the  nucleolus  or  nucleoli  divide  into  parts 
and  are  distributed  about  the  chromatin  masses.  By  the  time  that  the 
chromatin  thread  (skein)  is  divided  into  chromosomes,  these  latter  have 


46 


PROTOPLASM  AXD  THE  CELL 


arranged  themselves  around  the  nucleus  in  a  broken  ring  (B),  and  the 
centrosomes,  still  connected  bv  the  conspicuous  rays  of  the  asters,  are 
on  opposite  sides  of  the  nucleus.  The  nuclear  reticulum,  arranged  in 
parallel  lines,  helps  to  connect  them  through  the  mass  of  the  now  fast 
dividing  nucleus.  This  whole  structure,  the  two  asters  and  the  nucleus, 
called  the  diaster;  the  connecting  fibrils  (possibly  contractile),  the 
nuclear  spindle.  So  far  no  actual  division  of  any  structure  has  taken 
place,  the  process  up  to  this  point  consisting  only  of  the  separation  and 
proper  preliminary  arrangement  of  structures,  either  dual  or  numerous. 
These  processes  together,  then,  make  up  the  "prophases"  of  mitosis 


Fig.  19 


Diagram  of  mitotic  cell-divi.sion.      (Flemming. 

The  next  step,  the  most  difficult  to  explain  (although  not  to  describe) 
in^the  whole  marvellous  mitotic  process,  consists  in  the  longitudinal 
halving  of  each  of  the  chromosomes,  each  lateral  half  of  each  particle 
of  chromatin  "  thread"  then  beginning  to  separate  from  its  former  half  (C). 
It  gradually  makes  its  way  outward  (D)  through  what  was  formerly  the 
mother-nucleus,  now  called  the  nuclear  spindle,  to  its  centrosome  and 
aster,  one  of  which  still  remains  on  each  side.  This  separation  (E)  of 
the  chromosomes  into  lateral  halves  is  called  the  "metaphase"  and  the 
succeeding  events  the  "anaphases"  of  mitosis.  As  the  new  chromatin- 
masses  approach  the   centrosomes  on  cither  side  a  constriction   (F)   is 


PROTOPLASMIC  FUNCTION  47 

taking  place  around  the  periphery  «f  tiie  cytoplasm  in  a  plane  half-way 
between  the  asters,  and  this  constriction,  deepening,  finally  cuts  the 
mother-cell  completely  into  two  parts,  the  new  daughter-cells.  The 
chromatin  masses,  thickening,  now  gradually  arrange  themselves  appar- 
ently on  the  reticulum  about  the  new  attraction  spheres,  the  rays  disap- 
pear, a  nuclear  membrane  forms,  the  periphery  of  the  cytoplasm  rounds 
itself,  and  the  two  new  cells  are  become  miniature  replicas  of  their 
mother-cell. 

Heredity  axd  Adaptation'. — Heredity  and  adaptation  are  two 
opposed  phases  of  the  phylogenic  or  continued  racial  life  of  animals. 
Heredity  may  be  defined  as  that  protoplasmic  principle  or  faculty  by 
which  cells  tend  to  be  like  the  parent-cells  from  which  they  spring. 
Adaptation  is  the  tendency  of  new  protoplasm  to  adjust  itself  struc- 
turally and  functionally  to  the  conditions  of  its  environment.  It  is  only 
by  the  constant  interaction  of  these  two  tendencies  of  all  protoplasm 
that  life  can  continue  unendinglv.  If  onlv  hereditv  determined  the 
characters  of  offspring,  life  would  soon  be  overcome  by  an  ever- 
changing  physical  environment. 

On  the  other  hand,  were  protoplasm  too  plastic,  living  forms  would 
lack  that  constancy  of  characteristics  which  marks  each  of  them  off 
from  the  rest  of  the  world.  These  two  indispensable  and  interdependent 
tendencies  are,  therefore,  functions  inherent  in  all  protoplasm.  Like 
the  other  dispositions  already  considered,  they  are  immediately  dependent 
(1)  on  the  fluidity,  (2)  on  the  atomic  or  molecular  comflex^ty ,  and  (3) 
on  the  extreme  instability  of  the  living  substance.  These  qualities  of 
protoplasm  have  already  been  described  and  explained.  They  are,  in 
fact,  probably  only  different  views  or  statements  of  the  leading  property 
of  biogen; — its  extreme  plasticity.  By  this  property  protoplasm  is  capable 
of  receiving  on  the  one  hand  all  the  qualities  of  its  parent  protoplasm, 
and  on  the  other  hand  of  accepting  an  impression  from  every  surround- 
ing influence,  great  or  small. 

It  is  not  difficult  to  imagine  in  regard  to  heredity  that  which  has  no 
actual  biological  existence,  and  yet  herein  is  apparently  one  of  the  great- 
est mysteries  of  all  of  Nature's  secrets.  At  the  present  time  we  cannot 
well  imagine  how  a  body  of  jelly-like  matter  so  minute  as  to  be  invisible 
to  the  naked  eye  should  be  the  sole  means  of  transmitting  from  a  man  to 
his  son  not  only,  sometimes,  the  whole  physical  constitution  of  that 
man,  but  his  mental  and  moral  nature  as  well,  habits  of  speech,  tenden- 
cies appearing  perhaps  scores  of  years  after  the  heredity-conveying 
speck  of  protoplasm  from  the  parent  is  gone.  The  whole  matter  is 
enormously  complex  and  inwrought  with  speculation  and  skepticism. 

An  Example  of  Relatively  Simple  Protoplasm:  Ameba. — Perhaps  the 
best  way  to  give  the  reader  an  idea  of  the  appearance  and  functions  of 
relatively  undifferentiated  or  primal  protoplasm  is  to  describe  one  of 
the  more  simple  animals,  in  fact,  the  most  simple  animal  known;  unless 
we  suppose  with  Hackel  that  there  lives  an  animal  still  more  simple 
in  that  it  lacks  a  nucleus — namelv,  the  monera. 


48  PROTOPLASM  AXD  THE  CELL 

The  ameba  is  generally  taken  as  the  most  typical  and  the  most  simple 
of  animal  cells.  It  has  for  us  additional  value  for  the  reason  that  it  is 
endowed  with  more  functions  than  many  sorts  of  tissue-cells,  because 
it  is  an  independent  and  separate  animal.  It  is  not  a  part  of  a  tissue 
with  only  one  or  two  processes  to  accomplish — e.  g.,  an  epithelial  cell  in 
a  mammal.  There  are  several  species  of  the  genus  ameba,  but  the  one 
most  typical,  largest,  and  best  adapted  for  description  is  ameba  proteus,. 
classed  zoologically  as  a  protozoan  rhizopod.  These  animals  are  often 
large  enough  to  be  seen  by  the  unaided  eye,  but  more  usually  are  only  a 
small  fraction  of  a  millimeter  in  diameter,  and  therefore  require  much 
magnification  for  study.  When  enlarged  about  three  hundred  diameters 
there  can  be  seen  a  mass,  irregular  in  shape,  of  a  substance  which  looks 
like  granular  jelly  in  the  bottom  of  the  water  drop  on  the  slide  of  the 
microscope.  Around  the  edges  of  the  mass  the  jelly-like  protoplasm  is 
freer  of  granules  than  it  is  within.  This  more  or  less  transparent  tem- 
porary edge  of  the  animal  is  called  the  ectoplasm,  and  the  inner  and  more 
granular  portion  the  endoplasm,  distinctions  which  are  of  slight  signifi- 
cance. Near  the  centre  of  the  animal  is  a  small  spherical  body,  often 
darker  than  the  surrounding  protoplasm,  which  may  be  encircled  by  a 
more  or  less  transparent  ring.  This  rounded  mass  is  the  nucleoplasm 
or  nucleus.  The  rest  of  the  cell  is  called  the  cytoplasm.  Within  the 
nucleus  there  is,  although  exceeding  small,  a  still  darker  dot,  which  is 
the  nucleolus,  of  unknown  significance.  About  the  nucleus,  or  here  and 
there  through  the  cytoplasm  generally,  are  seen,  sometimes  prominently, 
w^hat  appear  like  bubbles,  but  which  are  spaces  filled  with  clear  li(juid, 
but  not  a  gas.  ]\Iost  of  these  vacuoles,  as  they  are  mistakenly  called, 
are  constant  and  unchangeable  in  size,  and  are  termed  permanent 
vacuoles.  One,  larger  than  the  rest  ordinarily,  may  be  seen  to  grow 
slowly  and  to  disappear  suddenly  (by  bursting)  when  it  has  reached  a 
certain  size;  this  is  the  contractile  vacuole.  Close  examination  shows 
the  whole  nucleus  to  be  pervaded  with  small  masses  of  a  more  opaque 
substance  called  chromatin,  w^hile  with  a  very  high  magnification,  the 
cytoplasm,  apparently  homogeneous  with  a  low  power,  shows  a  minute 
reticular  structure,  as  if  made  up  of  a  mass  of  li(|uid  foam.  The  status 
of  the  distinct  granules  is  not  yet  clear.  Despite  their  name,  metaplasm, 
they  probably  are  a  part  of  the  protoplasm.  These,  then,  are  the 
"organs"  of  ameba  in  its  normal  condition.  Sometimes  other  objects 
within  its  mass  may  be  noted.  For  example,  there  may  be  seen  par- 
ticles of  food  fa  vegetable  cell  or  a  diatom)  or  a  piece  of  the  waste  left 
from  the  digestion  of  .such  a  meal.  These  particles,  while  in  process  of 
digestion,  may  be  surrounded  by  visible  vacuoles,  in  which  case  the 
latter  are  filled  with  digestive  juices.  The  finer  structure  and  signifi- 
cance of  these  various  organs  will  be  described  later,  our  endeavor  now 
being  to  gain  an  understanding  of  how  prolo})iasin  appears  and  what 
animals  maile  of  it  do.     (See  Fig.  1.) 

It  would  be  rliffifult  to  distinguish  an  aincba  from  die  multifarious 
debris  of  tlic  pool-l)f)ttoni  in  wliicli  it  is  to  l)c  found  were  it  not  that  obser- 


PROTOPLASMIC  FUNCTION  49 

ration  suggests  that  the  granular  ameboid  mass  (imlike  the  others)  is 
moving,  without  apparently  being  disturbed  from  the  outside.  Amebse 
are  continually  shifting,  in  fact,  with  a  sort  of  slow  motion  character- 
istic of  themselves.  If  the  animal  be  in  water  at  a  temperature  lower 
than  15°  C,  the  movement  may  not  be  perceptible  except  when  one 
repeatedly  draws  the  outlines  of  the  cell  at  intervals  of  several  minutes 
and  compares  the  drawings.  When  this  is  done,  it  is  at  once  obvious  that 
the  creature  changes  in  shape  if  not  in  position.  This  spontaneous 
movement  of  this  minute  drop  of  protoplasm  is  a  wondrous  thing,  but 
to  its  wonder  we  are  accustomed,  and  call  it  life.  The  pseudopod  ("false 
foot"),  as  it  is  called,  may  be  on  a  smaller  scale  and  extend  only  a  little 
way,  almost  as  a  point  of  protoplasm,  soon  withdrawing  again  or  else 
remaining,  while  others,  larger  or  smaller,  push  out  in  various  places 
and  directions.  Several  of  these  may  be  extending  themselves  at  one 
time,  some  large,  some  small,  some  dull,  some  pointed,  all  of  different 
shapes,  some  upward,  toward  the  objective  point  of  the  microscope  so' 
as  to  be  little  noticed,  the  size  or  bulk  of  the  cell  meanwhile  not  changing, 
but  only  its  shape.  It  is  evident  that  a  large  pseudopod  is  made  always 
at  the  expense  of  some  other  part  of  the  creature.  When  the  flowing 
occurs  in  one  direction  continually  the  animal  advances,  and  in  this  way, 
hither  and  thither,  it  creeps,  especially  out  of  open  spaces,  very  slowly 
and  indirectly,  over  the  bottom  of  the  drop  in  which  it  lies.  (See  Move- 
ment, page  3S.) 

The  fluidity  of  the  ameba  is  its  most  conspicuous  property;  without 
it  all  these  curious  "ameboid  movements"  would  be  impossible.  This 
is  true  of  almost  all  protoplasm.  The  mode  of  this  motion  in  detail  is 
characteristic.  With  a  high-power  microscope  it  may  be  readily  seen 
that  it  consists  of  a  curious  combination  of  rolling,  streaming,  and  push- 
ing particles,  the  movement  of  the  different  parts  of  the  bioplasm  being 
made  clear  by  the  metaplasmic  granules  which  are  so  conspicuous  in 
ameba.  This  liquid  motion  is  technically  known  as  protoplasmic  stream- 
ing. \\lien  stimulated,  as  by  a  jarring,  the  movement  ceases  and  the 
animal,  contracting  its  pseudopodia,  takes  a  shape  more  closely  approach- 
ing a  sphere  than  it  had  before.  This  shape,  however,  if  the  animal  be 
left  unstimulated,  soon  vanishes  in  the  ceaseless  pseud opod-making  and 
unmaking  just  described. 

Patience  in  observation  would  show  how  the  ameba  gets  its  food  and 
how  it  swallows  and  digests  it.  The  animal  appears  not  to  have  sense  of 
smell  or  taste  or  sight,  by  which  more  complex  animals  may  recognize 
their  food  at  a  distance.  It  has  some  sort  of  sense,  however,  such  that 
on  contact  with  a  bit  of  quartz  and  then  with  a  bit  of  nutriment,  it  will 
reject  the  quartz  and  ingest  the  food.  When  in  its  aimless  pseudopod ial 
creeping  the  animal  has  come  in  contact  with  a  particle  which  it  can 
digest  and  use  as  a  source  of  tissue  and  of  energy,  the  animal  at  once, 
but  in  its  characteristically  slow  w^ay,  sets  about  ingesting  it.  This  is 
often  a  difficult  task.  One  side  of  the  particle  is  surroimded  by  a 
pseudopod,  and  if  the  food  does  not  slip  away,  another  on  the  oppo- 
4 


50  PROTOPLASM   AXD   THE  CELL 

site  side  slowly  flows  out.  These  coalesce,  and  thus  the  piece  of  nutri- 
tious matter  is  surrounded  bv  a  living  net.  Sometimes  living  animals 
are  thus  entrapped.  The  cytoplasm  then  flows  in  upon  it  closely,  and 
the  particle  is  soon  in  the  interior  of  the  ameba.  Soon  a  vacuole  is 
produced  about  the  particle,  probably  by  a  process  of  secretion  from 
the  immediately  surrounding  protoplasm.  The  product  of  this  secre- 
tion, which  fills  the  vacuole  it  has  made,  is  undoubtedly  a  proteolytic 
enzvme  in  a  solution  such  as  that  which  digests  proteids  in  the  more 
highlv  evolved  animals.  While  digestion  is  going  on  the  nutritious  part 
of  the  food  is  al)sorbed  and  assimilated  to  the  ameba's  protoplasm.  The 
waste  is  excreted  by  a  method  homologous  to  that  by  which  the  food  was 
ingested — the  waste  particles  are  flowed  away  from  after  they  have  been 
gradually  worked  to  the  periphery  of  the  animal. 

The  effects  of  various  physical  agents  on  an  ameba  are  instructive. 
We  may  examine  first  as  to  heat.  Reduction  of  the  temperature  of  ameba 
causes  a  decided  slowing  of  the  ameboid  movements,  and  they  cease 
some  few  degrees  above  0°  C.  When  raised  above  20°  C.  or  so,  an 
average  room-temperature,  the  quickness  and  size  of  the  movements 
increase,  reaching  a  maximum  at  about  30°  C.  At  about  35°  C.  the  pro- 
toplasm goes  into  what  is  called  heat-rigor,  the  coagulation  being  com- 
pleted w^hen  the  temperature  is  at  40°  C.  or  a  trifle  higher.  To  light,  the 
ameba  reacts  under  ordinary  aquarium  conditions,  but  seeks  to  avoid 
it  when  too  strong.  It  discriminates  between  degrees  of  light  and  shade, 
and  this  is  only  a  general  protoplasmic  function.  If  a  weak  current  of 
electricity  be  passed  through  the  water  surrounding  the  animal,  its  pro- 
toplasm elongatesfby  electrotaxis)  and  turns  its  long  axis  in  the  direction 
of  the  current.  Pointed  pseudopodia  of  small  size  extend  outward, 
usually  toward  the  anode.  If  the  voltage  of  the  electricity  be  excessive, 
the  protoplasm  of  the  animal  is  broken  up,  disintegrated,  and  scattered 
in  a  characteristic  manner. 

Like  all  protoplasm,  that  of  ameba  requires  oxygen  for  its  metabolism. 
It  is  regularly  attracted  })y  an  excess  of  the  gas,  while  if  its  oxygen  supply 
be  cut  off ,  the  pseudopodial  movements  gradually  cease  and  the  animal 
becomes  more  or  less  spherical,  and  enters  into  the  condition  known  as 
necrobiosis,  or  death-in-life,  in  which  the  vital  functions  surely  but  gradu- 
allv  cease.  Occasionally  an  ameba  may  be  seen  to  reproduce  itself — a 
process  lasting  two  or  three  hour.s — by  its  usual  method  of  amitosis  or 
simple  nuclear  division.  (See  page  44.)  The  nucleus  may  be  seen  to  be 
constricting  in  one  diameter.  This  is  followed  by  a  similar  process  in 
the  cytoplasm  in  the  same  plane.  Finally,  after  only  a  thread  of  cyto- 
plasm connects  them,  the  daughter-cells  wholly  separate.  These  new 
cells,  which  are  like  their  parent  save  in  size,  proceed  in  their  functions 
.seemingly  as  the  mother  did  before  them — links  of  a  chain  which 
theoretically  has  no  end — the  protoplasm  composing  them  being  in  this 
limitf'd  sense  immortal.  The  ameba  also  has  to  conjugate  at  times  with 
another  iiulividna!  in  onh-r  to  maintain  continuously  the  descent. 

We  are  now  al)le  to  summarize  some  of  the  underlying  facts  and  ideas 


PLATE  II 


PROTOPLASMIC  FUNCTION  51 

which  an  observation  of  the  amel)a  has  given  us,  the  characteristics  of 
this  animal  by  which  it  is  the  most  typical  of  cells,  the  type  of  protoplasm. 
In  the  first  place,  the  protoplasm  of  the  ameba  has  a  certain  consistence, 
fluid  yet  capable  of  form.  It  has  structure  and  organs,  nucleus,  cyto- 
plasm, nucleolus,  a  contractile  vacuole,  one  or  more  permanent  vacuoles, 
and  chromatin  masses  in  the  nucleus;  it  is,  then,  a  morphological  thing 
and  concept.  The  ameba  moves  spontaneously  and  in  a  peculiar  way — 
namely,  by  flowing  slowly  or  streaming  back  and  forth  into  pseudopods 
and  out  again,  rolling,  pouring,  streaming  slowly  over  the  ground.  Heat, 
up  to  a  certain  temperature,  makes  protoplasm  more  active,  while 
cold  makes  it  less  so;  light  affects  it  in  this  animal,  and  electricity  influ- 
ences it  peculiarly.  The  protoplasm  of  the  ameba  requires  oxygen,  food, 
and  water  in  order  to  live;  it  absorbs  the  oxygen,  digests  and  assimilates 
the  food,  and  moves  only  In'  its  inherent  water.  Finally,  a  drop  of  proto- 
plasm in  this  animal  form  reproduces  by  dividing  itself  into  two  sub- 
stantially equal  parts,  which  thereupon  are  immediately  capable  of  all 
the  ameba's  functions. 


EXPLANATION   OF  PLATE   II. 

Plans  of  the  ner\-ous  systems  and  brains  of  animals  of  wdely  varying  complexity.  Nervous 
systems  of  177,  scallop  (Pecten);  178,  starfish  (Asterias);  179,  mollusc  (Unio);  180,  sea-mussel 
(Mytilus);  181,  a  mollusc  (Carinaria);  182,  a  mollusc  (Bullea);  183,  argonaut  (Nautilus);  184, 
cuttle-fish  (Sepia);  185,  a  parasitic  worm  (Strongylus);  186,  earthworm  (Lumbricus);  187,  a 
rotifer  (Hydatina);  188,  barnacle  (Lepas);  189,  a  marine  worm  (Aphroditea);  190,  a  myriapod 
insect  (Scolopendra);  191,  lar\-a  of  a  moth-insect  (Sphinx  ligustri):  A,  cephalic  ganglia;  192, 
same  at  time  of  the  first  change:  -4,  portion  of  thoracic  cord,  showing  respiratory  nerves;  B, 
view  of  ganglion  from  above;  C,  from  the  side;  193,  ner\'ous  system  of  the  pupa  of  Sphinx;  194, 
of  the  imago  of  the  same  insect;  195,  of  the  cockchaffer  (Melolontha);  196,  enteric  system  of 
the  locust  (Gryllus  migratorius);  197.  nervous  system  of  the  sand-hopper  (Talitrus);  198,  crab 
(Maia);  199,  spider.  In  the  following  figures  a  points  to  the  olfactory  ganglia;  b,  to  cerebral 
hemispheres  or  ganglia;  c,  to  optic  lobes  or  ganglia;  d,  to  the  cerebellum,  and  e,  to  the  spinal 
cord:  200,  brain  of  gurnard  (fish,  Trigla);  201,  conger  eel  (Murena);  202,  ray-fish  (Raia);  203, 
gray  lizard;  204,  frog  (Rana);  205,  green  turtle  (Testudo  mydas);  206-209,  development  of  ner- 
vous sy.stem  of  the  chick;  210,  brain  of  cassowary;  211,  lion;  212,  origins  of  spinal  ner\'es;  213, 
nervous  system  of  human  embryo  at  seven  weeks;  214,  brain  of  human  embryo  at  nine  weeks; 
215,  twelve  weeks;  216,  fifteen  weeks;  217,  twenty-seven  weeks;  218,  219,  brain  and  cord  of  frog- 
tadpole.      (Carpenter,  from  many  sources.) 


CHAPTER    11. 


THE   NERVOUS   SYSTEiVI. 


We  have  examined  into  the  basal  nature  of  the  substance  composing 
animal  bodies  so  far  as  it  may  readily  be  studied,  and  have  noted  its 


Fig.  20 
mesencephalon 


CHOROID    j 
PLEXOS~~ 
FORANaEN 
OF  MONRO 
CAUDATE 
NUCLEUS 


Op.  V. 


INFUNDIBULUM  PONS 


CEREBELLUM 

FOURTH 

VENTRICLE 


Dr^Mc:  ^,     !J_OBLONGATA 


Brain  of  calf-embryo  of  5  cm.,  to  show  the  bandings  of 
the  originally  straight  neural  axis.  Lateral  view  of  left 
side,  the  outer  wall  of  the  hemisphere  being  removed. 
(Hertwig.) 

activities.  We  can  now  discuss  the  func- 
tions of  the  human  body  systematically 
and  with  as  much  detail  as  our  space  al- 
lows. In  this  description  of  bodily  pro- 
ces.ses  we  must  first  understand  the  ways 
by  which  the  various  parts  and  functions 
of  the  body  are  coonh'natcd  so  as  to 
constitute  an  individual.  Animals  exist 
only  as  individuals,  and  in  part  at  least, 
as  the  name  implies,  are  separate  from 
each  other  and  more  or  less  independent. 
Without    a   [)roper  understanch'ng   of  the 

means  of  unification  of  the  various  functions  we  should  miss  the  full 
meaning  of  many  of  them  and  fail  utterly  to  take  that  broad  view  of 
animal  fife  which  is  .so  es.scntial  to  knowledge  and  invaluable  in  treating 
di.sea.sed  conditions.  We  should  never  think  of  tlie  animal,  then,  as  a 
group  of  organs  but  as  one  integral  organi.sm,  though  necessarily  made 
up  of  parts  more  or  le.ss  different  in  their  structure  and  uses.  It  is  ex- 
ceedingly irnf)ortaiit  to  kcej)  in  luiud  this  inherent  unification  and  to 
remember  that  it  is  for  dcscrij^tivc  purpo.ses  only  that  we  shoukl  separate 
the  organs  and  descrilx-  them  one  at  a  time.  In  reality,  as  they  live, 
they  are  in  no  .sense  independent  of  each  other.     One  of  the  means 


Very  early  state  of  the  central  ner- 
vous system  of  man :  1,2,3,  forebrain, 
midbrain,  and  hindbrain,  respectively; 
/,  telencephalon;  Op.  v.,  optic  vesicle; 
//,  diencephalon;  ///.mesencephalon; 
/I'.metencephalon;  I',myelencephalon. 
Farther  dr)wn  the  neural  groove  one 
.sees  the  somites  and  medullary  groove 
of  the  .-piiKil  cord.      (Hackel.) 


THE  GENERAL  FUXCTIOXS  OF  THE  NERVOUS  SYSTEM       53 

by  which  the  organs  of  the  body  are  coordinated  is  the  complex  and 
nearly  all-pervasive  system  of  bloodvessels  and  of  lymphatics.  The 
other  chief  means  is  the  nervous  system,  and  this  is  still  more  complex. 
(See  the  experiments  and  the  theoretical  notes  on  them  in  the  Appendix.) 
The  nervous  system,  then,  is  that  fabric  of  linear  structures  which 
serves  to  connect  in  a  functional  manner  the  various  parts  of  the  body, 
coordinating  them   into    an    individual,    just   as    the   connective-tissue 

Fig.   22 


A  leaf  of  Venus'  fly-trap  (Dionea),  much  enlarged.  Conductivity,  the  basal  function  of  the 
nervous  system,  and  a  process  common  to  all  protoplasm,  is  seen  well-developed  even  in 
certain  plants.  A  stimulus  (from  an  insect,  for  example)  applied  to  the  hair-like  projections  on 
the  edge  of  the  leaf  is  promptly  conveyed  to  the  (motor)  hinge  and  occasions  there  a  quick 
approximation  of  the  two  halves.  There  are  present  here,  then,  all  the  essentials  of  a  reflex 
action  (see  below)  and  of  a  useful  neuro-muscular  mechanism — the  immediate  agent  of  all  the 
world's  advancement. 

anatomically  binds  the  organs  and  parts  together.  The  nervous  tissue 
comprises  physiologically  a  vastly  complex  "protoplasmic  bridge"  (Loeb) 
between  cells  and  between  organs,  and  transmits  (more  or  less  changed 
perhaps)  the  myriad  influences  which  originate  in  these  organic  units. 
The  nerve-fabric  only  takes  up  and  perfects  in  the  biological  division  of 
labor  one  of  the  functions  of  all  protoplasm,  conductivity.  If  we  omit 
for  the  present  the  relations  of  the  nervous  system  to  the  mental  process, 
we  may  say  in  advance  that  the  function  of  the  nervous  system  is  almost 
wholly  conduction,  using  this  term  in  a  broad  way  to  include  coordination. 

THE  GENERAL  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 


The  general  functions  of  the  nervous  system  may  be  classified  as 
follows:  (1)  To  represent  consciousness,  at  least  as  a  connector  or 
coordinator;  (2)  to  receive  and  to  transmit  impulses  "inward,"  affer- 
ently;  (3)  to  direct  muscular  function:  (a)  actuating  it,  (b)  inhibiting 


54 


THE  NERVOUS  SYSTEM 


vh-- 


A 


-he 


Fig- 23  it;    (4)    to    direct   glandular  function: 

(a)  actuating  it,    (6)  inhibiting  it;  (5) 
to  direct  tissue-nutrition :  trophism. 

1.  The  nervous  system,  in  represent- 
ing consciousness,  as  the  general  though 
careless  presumption  is,  performs  its 
most  mysterious  function.  Yet  were 
it  not  for  the  fact  that  a  blow  on  the 
brain  destroys  consciousness,  while  one 
on  a  mass  of  muscle  does  not,  we  could 
not  perhaps  claim  that  the  nervous  sys- 
tem transmits  consciousness  any  more 
than  does  the  muscular  tissue,  or  the 
bones,  or  the  protoplasm  of  the  liver. 
Consciousness  and  living  bodies,  so  far 
as  we  know,  are  inseparable ;  more  than 
this  cannot  be  said.  How  completely 
the  nerves  represent  the  mind,  then, 
we  do  not  know,  but  they  apparently 
do  so  by  unifying  the  functions  of  the 
organism,  and  by  coordinating  the  pro- 
toplasmic activities  into  the  "physical 
basis"  of  a  personality. 

2.  The  animal  body,  like  the  mind, 
is  a  part  of  Nature,  and  as  such  is  in  the 
closest  possible  relation  with  its  environ- 
ment. The  nervous  system  has  to  adapt 
the  organism  to  this  environment, 
especially  to  changes,  among  others, 
in  the  kind  and  amount  of  its  nutrients 
and  in  its  amount  of  moisture,  heat, 
pressure,  light,  and  oxygen.  All  these 
and  numerous  other  conditions  help  to 
determine  the  reactions  of  the  body, 
and  should  be  regarded  by  the  dys- 
chophysical  organism  every  moment 
of  its  life.  It  is  the  inward  (aiferent 
or  centripetal)  impulses  which  convey 
to  the  reflex  and  voluntary  centers  of 
the  nervous  system  knowledge  of  these 
and  many  other  conditions  of  the  envi- 
ronment. 

3.  In  the  direction  of  muscular 
contractions,  producing  both  molec- 
ular and  molar  movements,  the  ner- 
vous system   controls  and  coordinates 

the  deliberate  voluntary  movements,  and  the  instinctive  and  emotional 
(reflex)  reactions  of  the  organism.    It  does  this  l)oth  by  actuating  them 


^-^r 


^u^ 


le 


The  brain,  cord,  and  sympathetic  chain 
of  the  dove:  vh,  forebrain  (hemispheres); 
lo,  optic  lobe;  kh,  cerebelhjm;  06,  me- 
dulla oblonRata  ("bulb");  tr,  trigeminal 
(fifth  crania!)  nerve;  f/,  .^r'i'ial  ganglion; 
rw,  Hpinal  cord;  «?/,  sympathetio;  fce,  dor- 
sal enlargement;  le,  luintiar  enlargement; 
/,  filum  terminale.      (B.  Iluiler.) 


THE  GENERAL  FUNCTIONS  OF  rilE  NERVOUS  SYSTEM       55 


Fig.  24 


(settiiiii'  them  in  motion)  and  l)y  inhil)itin<)j  or  checking  them.  From  an 
area  of  the  cerebral  cortex  around  or  in  front  of  the  Rohmdic  fissure  and 
less  tlian  7  cm.  by  3  cm.  in  size,  miUions  of  muscle-fibers  throughout  the 
opposite  side  of  the  body  are  directed  to  contract  or  not  to  contract. 
The  millions  of  possible  combinations  of  these  numberless  muscle- 
fibers  produce  in  various  degrees  all  the  intricate  muscular  movements 
and  adjustments  of  civilized  man.  Every  one  of  these  many  thousands 
of  muscle  fibers  should  be  made  to  contract  in  the  proper  sec[uence,  long 
enough  and  not  too  long,  fast  enough  yet  not  too  fast,  and  hard  enough 
and  not  too  hard,  to  serve  the  intended  purpose.  We  are  but  now,  with 
the  developing  knowledge  of  the  conducting  mesh  which  seems  to  make 
up  the  more  essential  part  of  the  neural  tissue,  beginning  to  realize 
adequately  the  extreme  complexity  and 
perfection  of  this  function  of  the  nervous 
svstem.  The  neurone  has  something  of  a 
new  aspect.  Perhaps  the  cerebellum  has 
more  to  do  with  actuating  the  movements 
than  has  the  Rolandic  area;  so,  at  least, 
some  investigators  have  recently  claimed. 

Muscular  movements  are  classified  as 
(1)  deliberately  voluntary ;  (2)  reflex;  and 
(3)  "automatic"  or  autochthonic.  Volun- 
tary muscular  movements  are  those  made 
with  the  immediate  choice  or  will  of  the 
individual.  Some  biologists  consider  these 
the  primary  movements  in  the  evolving 
series  of  life.  When  they  had  beerl  per- 
formed often  enough  and  generation  after 
generation  long  enough,  they  became  re- 
flex, and  no  longer  required  an  act  of  will 
for  each  performance;  they  were  controlled 
then  by  centers  situated  especially  in  the 
spinal  cord.     Those  movements,  however 

(e.  (/.,  the  heart-beat,  peristalsis),  which  are  of  universal  need  and  occur- 
rence, have  gone  a  step  farther  and  have  become  "automatic,"  though 
recjuiring  actuation  from  the  central  nervous  system  for  control.  The 
law  of  habit,  then,  has  determined  the  status  of  the  various  muscular 
viscera.  These,  or  some  of  them,  have,  it  is  possible,  learned  to  act  per- 
fectly as  long  as  supplied  with  the  needful  amounts  of  nutriment,  heat, 
etc.  Thoracic  respiration  is  an  exceptional  sort  of  automatic  series  of 
movements  in  which  the  dominating  center  (in  the  medulla  oblongata) 
is  actuated  by  the  varying  quality  of  the  blood  flowing  through  it.  In 
this  case  the  nerve-center  is  automatic  rather  than  the  muscular 
mechanism. 

4.  In  controlling  glandular  action  (that  is,  epithelial  metabolism,  which 
usually  acts  to  produce  a  secretion  or  an  excretion)  the  nervous  system 
works  in  a  manner  similar  to  its  action  on  the  muscles.     The  epithelial 


The  nervous  net  about  a  ciliated  cell 
from  a  dog's  trachea.      (Ploschko.) 


56  THE  NERVOUS  SYSTEM 

cells  are  organs  made  to  produce  atomic  movements  just  as  the  muscles 
are  instruments  of  molar  movement.  Every  epithelial  cell  is  a  tiny 
laboratory  for  the  elaboration  of  some  new  substance,  and  the  nervous 
influence  coming  to  it  starts  or  stops  its  secretion.  "Whether  or  not  it  has 
any  qualitative  control  over  the  metabolism  is  still  somewhat  in  doubt. 
Whatever  the  nervous  authority  over  a  single  gland-cell  accomplishes, 
it  certainly  (a)  coordinates  the  actions  of  the  myriad  separate  cells,  and 
{b)  adapts  their  collective  action  to  the  needs  of  the  organism  as  a  whole. 
5.  Concerning  the  trophic  function  of  nerves,  the  influence  over  tissue- 
nutrition,  little  can  at  present  be  definitely  stated,  save  that  such  control 
undoubtedly  exists.  Whether  the  nerves  immediately  direct  the  nutrition 
of  any  tissue  is  not  determined,  but  the  function  of  coordinating  the 
nutrition  of  parts  is  surely  performed  by  the  nervous  system.  In  normal 
conditions  there  are  some  signs  of  this,  but  pathology  shows  us  numerous 
instances  in  which  a  disease  of  a  brain-part  results  in  trophic  disaster  in 
some  portion  of  the  organism  (e.  g.,  acromegaly).  This  trophic  control 
may  prove  to  be  identical  with  that  overglandular  action,  since  all 
protoplasm  appears  more  and  more  to  be  the  site  of  complex  chemical 
production.  The  nervous  energy,  whatever  it  is,  actually  stimulates  the 
energetic  processes  of  protoplasm.  When  cut  nerves  are  regenerated,  the 
first  function  to  recur  is  the  trophic  function:  the  part  slowly  regains 
its  lost  flesh-color,  its  warmth,  and  its  firm  tone.  Its  resistance  to  disease 
increases.  These,  then,  are  the  most  conspicuous  elements  of  "  trophism." 
(Sensation  next  appears,  then  reflex  movement,  and  lastly  voluntary 
movement.)  It  is  probably  through  this  trophic  control  over  tissue- 
metabolism  exerted  by  the  central  nervous  system  that  the  chronic 
emotion  of  worrv  exerts  its  baleful  influence  over  health.  (See  Chapter 
XII.) 

FEATURES  OF  THE  NEURAL  STRUCTURE. 

The  chief  function  of  the  nervous  system  is  coordination,  and  it  accom- 
plishes this  by  the  conduction  of  various  influences  between  large  or 
small  parts  of  the  body  and  l)etween  the  organism  as  a  whole  and  its 
environment.  For  this  conduction  fibers  are  necessary,  and  accordingly 
we  find  the  nervous  system  essentially  a  network  of  fibers  or  of  fibrils 
extending  almost  everywhere  in  the  body.  The  relations  of  these  fibers 
or  fibrils  making  up  the  neural  "reticulum"  are  not  yet  fully  understood, 
nor  are  its  relations  to  the  nerve-cells  which  are  so  numerously  connected 
with  it.  It  is  not  certain  that  the  fii)ril  rather  than  the  fil)er  (neuraxone, 
neurite,  neuraxis,  fibril-bundle,  axis-cylinder)  is  the  conducting  unit 
(that  is,  that  each  fibril  bears  a  separate  impulse),  but  the  probability  of 
this  belief  is  increasing. 

Throughout  most  of  their  length  ihc  sup])ose(l  fibrils  are  gathered  in 
bundles  (the  fibers,  axones),  and  these  are  of  several  diflVrent  sorts, 
classified  according  to  their  coverings.  The  essential  fiber  made  up  of 
fibrils  varies  little,  so  far  as  is  known,  save  in  diameter.    Two  chief  types. 


FEATURES  OF  THE  NEURAL  STRUCTURE 


57 


however,  are  coiniiionly  described,  the  mcdiillatcd  and  the  non-medul- 
lated.  In  both  of  these  the  fiber  eonsists  of  the  essential  fibrils  embedded 
probably  in  a  clear  substance  called  the  neuroplasm,  while  according  to 
a  few  observers  a  delicate  reticulum  is  also  present  in  the  fiber. 

In  the  nu'dullah'd Jihrrs  the  bundle  of  fibrils,  often  more  or  less  flattened 
and  irregular,  is  surrounded  bv  the  axolemma  and  then  bv  a  relativelv 
thick  covering  of  a  highly  refractive  substance  of  a  fatty  nature  called 
myelin,  this  covering  being  the  medullary  sheath  or  myelin  sheath.  The 
contained  myelin  is  kept  in  place  by  a  neurokeratin  network.  The 
sheath  is  divided  into  segments  by  oblicjue  fissures,  the  incisures  of 
Schmidt,  the  segments  bearing  the  name  of  Lantermann.  As  usually 
studied,  the  myelin  sheath  is  colored  black  by  osmic  acid.  In  the  periph- 
eral nerves  (mostly  cerebrospinal,  but  also  sympathetic  in  part)  the 
myelin  sheath  is  in  turn  covered  by  a  transparent  structureless  membrane 


Nen-es  of  a  mesenteric  lymph-gland  from  a  new-born  dog.      (.Manouelian.) 

called  the  neurilemma,  or  sheath  of  Schwann.  At  intervals  varying  with 
the  diameter  of  the  fibril-])undle  or  fiber  the  myelin  sheath  is  interrupted, 
these  interruptions  being  the  nodes  of  Ranvier,  and  it  is  through  these 
nodes,  apparently,  that  the  fiber  receives  its  nutriment  from  the  lymph 
and  excretes  its  katabolic  waste.  They  are  from  80  to  900  mmm.  apart, 
these  extremes  corresponding  to  fiber-diameters  of  about  2  and  25  mmm. 
respectively.  Each  of  Lantermann 's  segments  in  man  contains  one 
neurilemma-nucleus,  surrounded  by  a  small  amount  of  protoplasm. 
At  the  nodes  the  neurilemma  or  sheath  of  vSchwann  is  thickened,  being 
thus  continuous  along  the  fiber,  oftentimes  from  close  to  its  "origin"  in 
the  nerve-cell  nearly  to  its  termination. 

Non-mecluUated  fibers   (Remak's)   lack   the  myelin   sheath.     Usually 
they  are  surrounded  by  the  neurilemma,  and  are  then  from  about  4  to 


58 


THE  NERVOUS  SYSTEM 


7  mmm.  in  diameter.  In  the  prolongations  from  certain  ganglion-cells 
even  this  covering  is  apparently  lacking.  The  non-medullated  fibers 
have  a  grayish  color.    They  are  generally  in  the  sympathetic  system. 

Xcrve-ccUs  are  the  other  elements  of  the  nervous  system  besides  the 
conducting  fibers  or  fibrils.  They  vary  greatly  in  size,  for  while  the 
motor  cells  of  man's  spinal  cord  may  be  150  mmm.  in  diameter  (ranging 
upward  from  75),  some  of  the  nerve-cells  in  the  granular  layer  of  the 
cerebellum  have  a  diameter  of  not  over  4  mmm.,  while  others  are  twice 
as  large.  Xerve-cells  have  large  nuclei  and  nucleoli,  but  relatively  little 
chromatin.    There  is  usually  about  the  periphery  of  the  cell  a  non-granular 


Fig.  26 


Motor  nerve-cells  from  the  anterior  horns  of  the  spinal  cord:  a,  nucleus  with  its  conspicuous 
nucleosufi;  b,  stainable  substance  of  Nissl;  c,  neurite;  d,  implantation  cone.  Note  the  neuro- 
fibrils.     (Bates.)  _ 


layer,  and  proVjably  a  similar  clear  layer  around  the  nucleus.  The  prin- 
cipal fiber,  the  neuraxis,  or  axis-cylinder,  joining  a  nerve-cell  spreads  out 
into  a  cone-shaped  mass  (the  implantation  cone)  in  the  cell,  which  is  also 
free  of  granules.  In  other  parts  of  the  cells  there  are  fibrils  doubtless 
continuous  with  those  of  the  prolongation  from  the  cell;  very  fine,  highly 
refractive  biogenic  granules,  and  the  so-callefl  chromatophile  granules 
(Nissl  bodies,  tigroid  substance),  which  are  coarse  granules  or  flakes 
especially  abundant  about  the  nucleus,  and  continuous  into  some  of  the 
cell's  branches.  About  the.se  three  elements  of  the  nerve-cells,  and  others 
(e.  g.,  pigment)  which  it  is  needless  to  mention,  there  is  at  present  no 
little  di.scu.ssion  among  histologists.  Their  exact  respective  functions  are 
still  more  obscure;  in  fact,  little  is  definitely  known  of  the  use  of  any  of 
the  many  parts  of  a  nerve-cell. 

In  the  brain  the  cells  of  the  cerebellum,  of  the  retina,  and  of  many 
other  parts  are  small.  So  are  those  of  the  posterior  horns  of  the  cord, 
while  those  of  the  anterior  horns,  as  already  stated,  are  many  times 
larger.     Some  fompclciit   neurologists  (e.  (j.,  Campbell)  claini   that  on 


FEATURES  OF  THE  NEURAL  STRUCTURE 


59 


sectioning  and  staining  the  cortex  its  numerous  functional  divisions  are 
at  once  obvious  by  the  differences  in  the  cells  and  fibers.  The  brain-cells 
have  no  obvious  capsule.  In  the  ganglia  of  the  peripheral  nerves  are 
medium-sizetl  nerve-cells  which  have  around  them  the  neurilemma.  In 
the  sympathetic  system  and  in  other  places  are  cells  surrounded  by 
"baskets"  of  nerve-fibrils,  connecting  with  a  more  or  less  distant  cell. 


Fig.  27 


The  effects  of  overstimulation   (fatigue?)  on  the  motor  nerve-cells  of  a  cat:  o,  normal;  b,  after 
five  hours'  continual  stimulation.      (Hodge.) 


Frog 


Lizard 


Fig.  28 
Rat 


Man 


The  phylogenic  and  the  ontogenic  evolutions  of  the  pyramidal  nerve-cell  and  the  neurone. 
The  top  row  of  neurones  (from  left  to  right)  are  those  of  the  frog,  the  lizard,  the  rat,  and  man, 
respectively:  a,  b,  c,  d,  e  are  stages  in  the  embryological  development  of  the  pyramidal  cell. 
(Ramon  y  Cajal.) 


60 


THE  NERVOUS  SYSTEM 


These  important  networks  are  now  under  active  discussion;  their 
function  is  bv  no  means  understood. 

I  jThe  neurone  theory  of  the  structiu'e  and  action  of  the  nervous  system 
supposes  that  even  in  the  adult  this  system  is  made  up  entirely  of  distinct 
units  called  neurones,  which  do  not  connect  structurally  save  by  contact. 
Between  them  are  the  recondite  gaps  called  synapses,  to  which  some 


Fig 


Diagram  of  some  of  tlie  ncuniiie;;  concenif'd  in  the  cpntral  nervous  system:  A,  cortex  cerebri; 
B,  spinal  cord;  C,  muscle-cells  and  the  teleodendrites  of  a  motor  spinal  neurone;  D,  a  peripheral 
afferent  (sensory?)  surface;  G,  .s|)inal  ganRlion;  a,  tlie  iieuiaxone  of  a  corticospinal  neurone;  6, 
the  teleodendrites  of  the  same  in  the  anterior  gray  horn;  c,  tlie  neuraxone  of  an  afferent  spinal 
neurone;  d,  the  peripheral  process  of  the  same;  e,  the  bifurcation  of  the  same;  /,  the  teleoden- 
drites of  the  same  connecting  with  the  dendrites  of  another  neurone,  g,  in  the  brain  somewhere. 
(Ramon  y  Cajal.) 

investigators  attril)utea  psychical  nature.  A  neurone  consists  of  a  nerve- 
cellfantj  nerve-fibers,  of  various  numbers  and  lengths  and  modes  of 
branching,  extending  from  it.  One  of  these  projections  is  usually  longer 
and  more  definite  and  tlirect  than  the  others,  and  is  called  the  neuraxis 
or  neuraxone.     This  neuraxis,  marked   also  bv  its  uniform  diameter, 


THE  CHEMICAL  COMPOSITION  OF  NERVE-TISSUE  61 

arises  generally  from  an  implantation-cone,  but  sometimes  from  one  of 
the  other  branches  (dendrites)  close  to  or  at  some  distance  from  the  cell- 
bodv  of  the  neurone.  From  the  neuraxes  of  the  Purkinje  cells  of  the  cere- 
bellum, of  the  pyramidal  cells  of  the  cortex  cerebri,  of  certain  cells  of  the 
cord, etc.,  fine  branches  or  collaterals  are  given  off,  usually  at  right  angles  to 
the  n'euraxis.  Sometimes  the  neuraxes  are  very  long(for  example,  they  may 
extend  from  the  cord  to  the  feet),  and  much  less  often  they  break  up  soon 
into  arborizations.  At  the  peripheral  extremities  of  all  those  which  do 
not  so  divide,  there  is  a  tuft  of  fibrils  called  teleodendrites.  In  the  course 
of  a  nerve  the  neuraxes  seldom  branch  (save  as  the  fine  collaterals),  but 
near  their  terminations  they  frequently  divide  into  two,  three,  or  more 
fibers  of  a  size  similar  to  that  of 

the   neuraxis.     It   is   part  of   the  F'«- ^i 

neurone  theory  that  the  axis-cvlin- 
der  is  the  centrifugal  path — i.  e., 
the  fiber  along  which  impulses  pass 

Fig.  30 


Neuronal  terminations  in  secreting  epithe- 
lium: A,  a  cell  from  a  rabbit's  parotid  gland; 
B,  a  cell  from  mammary  gland  of  a  cat  dur- 
ing gestation.  Observe  that  the  nerve-endings 
do  not  connect  with  the  nuclei.      (Morat.) 


Perivascular  plexus  of  nerve-fibrils. 
(Ramon  y  Cajal.) 


outward  from  the  cell-body.  Besides  this  "centrifugal"  branch,  most 
neurones  have  "centripetal"  projections  called  dendrites.  These  may 
be  only  few  in  number  or  very  numerous,  and  often,  as  in  Purkinje's 
cells  of  the  cerebellum,  have  arborizations  of  great  extent  and  complexity. 
Sometimes  the  dendrites  appear  like  collaterals,  or  even  like  neuraxes, 
and  may  then  have  terminal  claw-like  teleodendria  like  those  of  the  latter. 
In  some  cases  the  dendrites  are  arranged  like  a  basket  closely  around  the 
nerve-cell  of  the  next  neurone  in  the  functional  series.  But  the  respective 
uses  of  all  these  structures  are  not  well  understood. 


THE  CHEMICAL  COMPOSITION  OF  NERVE-TISSUE. 

The  facts  as  to  neural  composition  are  clearly  of  more  and  more 
importance  as  they  become  better  understood.  Sooner  or  later  the  chem- 
istry of  the  nervous  system  will  throw  much  light  on  the  real  nature  of  its 
activity,  about  which  so  little  is  now  known  with  certainty.    ]Many  things 


f52  THE  NERVOUS  SYSTEM 

in  phvsiologv,  as  in  psychology,  depend,  for  example,  on  the  nature  of  the 
nervous  impulse,  and  this  depends  on  the  chemical  composition  and  on 
the  metabolism  of  the  neural  tissue. 

The  amount  of  water  in  the  nervous  system  and  in  the  white  and  gray 
matter  varies  greatly  according  to  age.  In  a  fetus  the  white  matter 
appears  to  contain  about  87  per  cent,  of  water  and  the  gray  matter 
92  per  cent.  In  adults  the  percentage  of  water  in  the  white  matter  is 
about  GO,  and  in  the  gray  matter  about  S3;  while  in  old  age  the 
percentages  of  both  are  somewhat  higher.  From  this  it  will  be  seen 
that  nervous  tissue  is  about  four-fifths  water,  and  that  the  gray  matter 
(cells  and  unraedullated  fibers)  contains  more  water  than  white  matter, 
especially  in  the  prime  of  life.  The  gray  matter  contains  less  than  17 
per  cent!  of  solid  materials,  and  we  see  herein  the  physical  basis  of  its 
great  activity.  Among  the  solids  of  the  nervous  system  may  be  noted 
proteids,  nuclein,  neurokeratin,  cerebrins,  cholesterin,  various  extrac- 
tives (such  as  creatin,  xanthin,  lactic  acid,  uric  acid),  gelatin  from  the 
adherent  connective  tissue,  and  inorganic  salts.  Of  the  proteids,  the 
gray  matter  has  the  largest  proportion,  51  per  cent.,  according  to 
Halliburton.  These  are  a  nucleoproteid  and  two  cell-globulins,  one 
of  which  coagulates  at  a  temperature  as  low  as  47°  C.  (a  possible  cause  of 
death  from  sunstroke  and  from  high  fever).  The  cerebrospinal  liquid  is 
much  like  lymph  in  the  matter  of  inorganic  salts,  but  it  contains  only 
a  trace  of  proteid.  One  of  its  constituents  is  a  substance  (perhaps 
dextrose)  that  will  reduce  Fehling's  solution. 


THE  BLOOD-SUPPLY  OF  THE  NERVOUS  SYSTEM. 

The  nervous  system  receives  proportionally  more  blood  than  do  most 
of  the  organs  of  the  body,  as  the  unique  circle  of  Willis  at  the  base  of  the 
brain  and  the  ample  sinuses  about  the  hemispheres  indicate.  At  present 
little  is  definitely  known  about  the  vasomotor  system  of  the  nerves  and 
the  brain,  but  that  it  is  elaborate  is  becoming  more  and  more  evident. 
Recent  researches  by  Weber,  Bourgery,  and  Cavazani  have  shown  by 
anatomical  and  physiological  experiments  that  a  vasomotor  mechanism 
exists  in  the  V)rain,  while  Obersteiner  has  worked  out  somewhat  systemati- 
callv  its  nerve-fibers.  The  ventricles  of  the  cerebrum  are  portions  of  an 
hvdraulic  svstcin,  parts  of  which  surround  the  brain  and  the  cord.  About 
the  whole  brain  is  the  ])ia  mater,  lining  the  skull  is  the  dura  mater,  while 
between  these  is  the  arachnoid,  which  is  ])robably  an  important  osmotic 
membrane.  The  hydraulic  cavity  in  c|uestion  is  the  space  beteen  the  pia 
mater  and  this  membrane.  The  li(|uid  filling  it  (a  very  thin  lymph) 
communicates  freely  with  the  ventricles  in  the  brain  through  many 
canals,  the  largest  of  which  are  the  foramens  of  lAischka  and  Majendie. 
By  osmosis  the  lymj)h  of  this  subarachnoid  space  communicates  with 
the  venous  blood  in  the  su})dural  sinus.  Thus,  there  is  a  set  of  large 
vascular  cavities  in  (lie  interior  and  about  tlie  periphery  of  the  brain,  and 


FUNCTIONAL  PARTS  OF  THE  NERVOUS  SYSTEM 


63 


Fir;.  32 


the  (liferent  parts  of  these  can  exert  on  the  brain  all  degrees  of  local  or 
general  pressure,  as  normal  function  demands.  Osmosis  may  have  much 
to  do  with  these  adaptive  movements  of  liquid.  Only  few  details,  how- 
ever, of  these  vasomotor  activities  have  so  far  been  obtained,  but  there  is 
little  doubt  that  the  conditions  are  complex  and  important.  Perhaps  the 
pituitary  body  has  chemical  control  over  the  blood-supply  of  the  brain, 
for  it  seems  to  contain  a  vasoconstrictor  principle  thirty  times  as  strong 
as  adrenalin.  (See  Chapter  on 
Nutrition.)  The  reciprocal  vaso- 
motor action  between  the  trunk 
and  limbs  and  the  blood-supply 
of  the  head  has  long  been  a  well- 
known  fact. 

Another  function  of  this  "water 
jacket"  of  the  brain  is  to  protect 
it  from  injury  by  blows  on  the 
skull.  The  spinal  cord  is  supplied 
with  blood  by  arterioles  extending 
inward  from  the  pia  mater.  Cap- 
illaries are  especially  abundant 
about  the  nerve-cells,  especially  in 
the  cortex  cerebri.  The  imme- 
diate dependence  of  the  brain's 
function  on  ample  and  continuous 
blood-supply  is  the  most  com- 
plete found  in  the  body.  Allien 
the  flow  of  blood  ceases  or  even 
slows  greatly  the  central  functions 
cease.  Illustrations  of  this  fact 
are  seen  in  the  instant  dropping 
dead  of  people  when  the  heart 
stops  beating  or  bursts. 


a 


Diagrammatic  suggestion  of  an  arachnoidal 
villus  and  its  coverings:  co,  gray  cortex  of  the 
hemisphere;  p,  pia  intima;  sa,  subarachnoidal 
space  continuous  with  the  villus,  pa;  a,  arachnoid; 
sd,  subdural  space,  continuous  with  that  of  the 
villus,  sd^;  d,  inner  laj-er  of  the  dura  mater  sep- 
arated from  the  upi^er  layer,  (d/)  by  the  venous 
.space,  v;  ds,  dural  covering  of  the  arachnoidal 
villus.      (Rauber.) 


FUNCTIONAL  PARTS  OF  THE  NERVOUS  SYSTEM. 


Certain  portions  of  the  nervous  system  shoukl  be  especially  studied 
because  of  their  diagnostic  importance  if  for  no  other  reason,  though  little 
is  known  about  some  of  them.  We  will  consider  briefly  the  uses  of  the 
hemispheres  (including  their  much-discussed  cortex),  the  cerebellum, 
the  medulla  oblongata,  the  optic  thalami,  the  corpora  striata,  and  the 
pons. 

The  Hemispheres. — ^The  hemispheres,  or  cerebrum,  as  they  are  some- 
times called,  are  the  large  convoluted,  seamed  masses  of  white  protoplasm 
which  are  seen  in  the  opened  skull  when  the  tough  dura  mater  and  the 
thin  arachnoid  and  pia  mater  ("meninges"  of  the  brain)  have  been  cut 
through.    The  hemispheres  in  man  cover  over  all  the  remainder  of  the 


64 


THE  XERVOUS  SYSTEM 


brain — a  fact  of  instructive  contrast  with  all  animals  below  the  mam- 
malian complexity,  for  in  them  it  remains  anterior  to  the  rest  of  the 
brain.     In  a  young  human  embryo  this  same  anterior  position  prevails, 


Fig.  33 


Gyni^  prnicalu 
Corpus  idloiuiu 


Septum  lucidum 
Columna:  jornicis.-^ 

Corpus  striatum.- 
Stria  lerminalis 
Thalamus  opticus. 
Pulvinar. 


Brachiiim  conjunc- 

tiivm  posticum. 

Pedunculus  cerebri 

(  ad  corpora 
guadrigem- 
iz    I       ina. 

^"^  <   ad  medulla  m 
oblongalam. 

L  ad  pontem 


Ala  ctner 
Ob, 


runtruUfi  gracilis 


'J  lic  luimiiii  Vjrain,  witliin. 


a'put  nuclei  caudali. 

Cap^iila  interna 
(anterior  limb). 

Capsula  externa. 
Island  of  Reil. 
■Nucleus  lentijormis. 

laustrum. 


C  apsula  interna 
{posterior  limb). 

Thalamus  opticus. 

Corpus  geniculatum 
mediale. 

Cauda  nuclei 
audati. 


Hippocampus. 


Calcar  avis. 


but  what  is  then  only  a  small  protubcnmce  in  front  on  each  side  gradually 
grows  outward  and  backward  until  at  i>irtli  (he  "lobes"  of  the  cerebrum 
cover  over  all  the  rest,    'i'liis  preponderance  is  doubtless  an  index  of  the 


FUNCTIONAL  PARTS  OF  THE  NERVOUS  SYSTEM 


65 


superior  complexity,  capability,  and  iiitcllitjence  of  man.  Exactly  in 
what  way,  however,  the  two  facts  are  connected  cannot  he  precisely  told. 
Perhaps  the  excess  in  the  human  brain  over  the  brute's  brain  is  taken  up 
in  paths  for  the  association  of  organic  events  of  many  sorts,  this  increased 
association  making  possible  a  much  larger  number  of  actions,  bodily 
and  mental,  than  the  small-hemisphered  simpler  animal  can  perform. 


Horizontal  section  in  the  hemispheres  through  the  ganglia:  1,  2,  longitudinal  fissures,  former 
between  frontal  lobes,  latter  between  occipital  lobes;  3,  anterior  part  of  corpus  callosum;  4,  fissure 
of  Sylvius;  5,  island  of  Reil;  6,  caudate  nucleus  of  the  corpus  striatum;  7,  the  lenticular 
nucleus  of  the  same;  8,  optic  thalamus;  9,  internal  capsule;  10,  external  capsule;  11,  claustrum. 
(Dalton.) 

At  any  rate,  the  relative  size  of  the  cerebrinii  usually,  but  in  a  general  way 
and  with  many  exceptions,  corresponds  to  the  complexity  of  the  animal's 
life.    Thus,  e.  g.,  women  and  ants  have  relatively  large  brains. 

The  hemispheres,  like  the  nervous  system  in  general,  are  composed  of 

gray  matter  (nerve-centers)  and  white  matter  (fibers).     The  way  in  which 

these  two  sorts  of  tissue  are  disposed   is  best  shown  by  a  transverse 

horizontal  section  such  as  is  illustrated  in  Fig.  34.     Above  the  level  of  the 

5 


66 


THE  NERVOUS  SYSTEM 

Fig.   35 


OccipilaL-Po^- 

Hemispheres  from  above.      (Eberstaller.) 


Fig.  36 


Hemispheres  from   Jjelow.      (Eberstaller.) 


FUNCTIOXAL  PARTS  OF  THE  NERVOUS  SYSTEM 


67 


corpus  callosuiii  the  gray  mafier  lies  wholly  in  the  cortex,  but  below  that 
level  the  gray  matter  constitutes  the  corpora  striata,  the  optic  thalami, 
the  lenticular  nuclei,  etc.,  as  well  as  the  cortex.     The  functions  of  these 


Fig.   37 


Left  hemisphere,  dorsolateral  surface.     (Eberstaller.) 

various  nuclear  regions  will  be  considered  later.  The  v:hite  matter  of  the 
cerebrum  seems  to  be  made  up  of  fibers  which  conduct  impulses  from  one 
part  of  the  brain  to  another,  and  especially  from  the  cortex  on  all  sides, 
inward  and  downward,  and  which  constitute  more  or  less  directly  the 

Fig.   38 


Right  hemisphere,  mesial  surface.      (Eberstaller.) 

spinal  cord  and  the  cranial  nerves  passing  outward  within  the  skull. 
Above,  these  fibers,  converging  toward  the  pons,  start  from  the  cortex 
as  the  corona  radiata,  and  farther  down  they  are  called,  misleadingly, 


68 


THE  XERVOUS  SYSTEM 


the  internal  capsule.  This  is  simply  the  laterally  bent  and  flattened  sheaf 
of  fibers  from  the  cortex  where  they  pass  between  the  lenticular  nucleus 
on  the  outside  and  the  corpora  striata  and  optic  thalami  within,  as  the 
illustration  shows.  Similarly,  the  mysterious  corpus  callosum  is  a  thick, 
hard  bundle  of  fibers  connecting  intimately  the  two  hemispheres.     Not 

infrequently,  however,  it  is  absent 
^'^-  ^^  altogether  without  obvious  func- 

tional  defect  in  the  individual.  In 
an  homologous  way  the  lower  or 
temporal  convolutions  exhibit  con- 
verging fans  of  fibers  passing  in- 
ward and  upward  into  the  crura 
of  the  brain.  What  sorts  of  im- 
pulses, and  in  what  directions, 
these  various  fibers  conduct  will 
be  somewhat  better  understood 
when  the  functions  of  the  cortex 
cerebri  and  the  nuclei  which  they 
serve  have  been  described. 

The  Cerebral  Cortex. — This  is 
the  outermost  or  bounding  layer 
of  the  hemispheres,  and  is  from 
2  to  4  mm.  in  thickness  in  differ- 
ent parts.  The  area  of  the  cortex 
is  increased  tAvo  or  three  times  at 
least  by  the  numerous  sulci  and 
fissures,  2  or  3  cm.  deep,  in  the 
surface  of  the  hemispheres.  The 
cortex  dips  down  into  these  sulci 
in  all  cases  and  lines  them  on 
both  sides  and  on  the  bottom. 
Indeed,  these  sulci  appear  to  be 
present  for  the  purpose  of  increas- 
ing the  area  of  the  cortex,  and  they 
are  more  numerous  and  deeper 
the  more  highly  evolved  and  the 
more  skilful  and  intelligent  the 
animal.  The  cortex  is  composed 
of  various  layers  of  nerve-cells 
and  the  fibers  connecting  them. 
A  recent  estimate  of  the  number  of 
these  cells  in  the  human  cortex  is  0,2(IO,(1()(),()00;  other  estimates  state 
that  the  number  of  these  cells  is  several  times  as  small.  They  weigh, 
however,  only  about  seventeen  grams.  The  rounded  masses  of  brain 
between  the  sulci  and  fissures  are  tlie  gyri  or  convolutions,  and  each  of 
these  has  a  name  corrcsj)(>ndiiig  (o  its  position  and  sha])e. 

Aside  from  (he  gnat  longitudinal  fissure  separating  the  hemispheres 


Section  of  iiuinan  iLTcliral  cortox,  to  su)bJt;i.;5t 
especially  the  immense  complexity  of  tlie  neuronal 
relations  (methods  of  Weigert  and  Golgi):  C.  Z.. 
clear  zone  havinR  no  nerve  fibers;  M .  P.,Kxner's 
plexuB  in  the  molecular  layer;  .1.  air.,  ambiguous 
ceil  stratum;  Subm.  P.,  submolecular  plexus; 
Gt.  P.  P.,  great  pyrarrJdal  plexus;  Pol.  P.,  poly- 
morfjliic  plexus;  W.,  white  matter.     (Andriezen.) 


FUNCTIOXAL  PARTS  OF  THE  NERVOUS  SYSTEM 


69 


down  to  the  corpus  callosiiin,  two  others  merit  special  notice  in  Physi- 
ology— namely,  the  central  fissure,  or  fissure  of  Rolando,  and  the  fissure 
of  Sylvius.  The  Roland ic  fissure  divides  the  frontal  lobe  from  the  parietal, 
and  extends  nearly  straight  from  about  the  middle  of  the  summit  of  the 
hemisphere  outward,  downward,  and  forward  to  a  point  more  or  less 
close  to  the  fissure  of  Sylvius.  The  Sylvian  fissure  divides  the  frontal 
lobe  from  the  temporosphenoidal  lobe.  It  extends  from  the  anterior  per- 
forated space  on  the  base  of  the  brain  outward  to  the  lateral  surface  of  the 
hemisphere,  and  thence  backward,  upward,  and  inward;  a  short  branch, 
the  ascending  limb,  extends  anteriorly  a  little  distance  from  below  the 


Fig.   40 


The  chief  paths  from  the  cortex  to  the  cord.      (Starr.) 

lower  end  of  the  fissure  of  Rolando.  Besides  these  there  are  several 
others  nearly  as  large  anatomically  which  divide  the  various  lobes  into 
convolutions,  and  there  are  many  smaller  fissures. 

The  old-time  phrenology,  so  largely  a  subject  of  discussion  in  the  early 
part  of  the  nineteenth  century,  is  no  longer  thought  of,  save  historically. 
It  was  based  on  a  wrong  psychology.  Even  today,  however,  neurology 
has  no  facts  which  can  take  the  place  of  this  system  of  brain  localization. 
We  are  not  sure,  even,  whether  in  any  given  mental  process  the  whole 
cortex  does  not  act  in  one  way  or  another.  The  more  recent  division  of 
the  cortical  surface  into  motor  areas,  sensorv  areas,  and  association  areas 


70  THE  NERVOUS  SYSTEM 

is  still  incomplete,  and  there  is  doubt  as  to  its  substantial  value.  It 
is,  however,  customary  and  so  provisionally  proper,  to  describe  certain 
areas  of  the  cortex  as  motor  and  sensory,  the  latter  especially  having  a 
definite  and  more  or  less  certain  value.  Other  regions  are  called  asso- 
ciation-areas. 

The  ]Motor  Areas  of  the  Human  Cerebru]\i,  in  which  it  has 
been  supposed  that  voluntary  or  deliberate  muscular  movements  are 
actuated,  are  thought  at  present  to  be  the  convolutions  anterior  to  the 
fissure  of  Rolando,  the  adjoining  posterior  part  of  the  frontal  lobe,  and 
that  portion  of  this  general  region  to  be  seen  on  the  mesial  surface  of  the 
hemispheres.  In  the  earlier  work  of  Ferrier,  Horsley,  Munk,  and  others 
on  monkevs  the  motor  area  was  found  to  occupy  the  posterior  central 
convolution  also,  but  it  has  lately  been  made  probable  by  Sherrington  and 
Griinbaum,  working  on  the  chimpanzee  (the  brute  most  like  man),  and 
by  the  embryological  studies  of  Flechsig,  that  the  area  just  posterior  to 
the  Rolandic  fissure  represents  in  man  cutaneous  sensation;  Farther 
back  the  important  muscular  and  joint  sensations,  known  as  the  kines- 
thetic impulses,  are  represented.  These  facts,  however,  are  simply  the 
products  of  stimulation  of  the  cortex  and  of  the  other  modes  of  experi- 
mental study  largely  on  speechless  animals.  It  is  likely,  on  the  whole, 
that  the  kinesthetic  sensations  of  a  muscular  part  have  their  "centers"  in 
the  same  brain-areas  as  do  the  movements  of  these  parts.  We  are  not 
then  certain  at  the  present  time  what  we  mean  by  "a  motor  area,"  since 
all  sorts  of  sensations,  feelings,  ideas,  etc.,  are  closely  related  to  the  con- 
traction of  muscles.  Adamkiewicz  has  recently  claimed,  as  a  result  of 
four  years  of  careful  research,  that  the  whole  cerebral  cortex  is,  properly 
speaking,  psychical,  or  at  least  psychomotor,  in  its  functions.  He  sup- 
poses, accordingly,  that  it  is  the  function  of  the  cerebellum  to  conduct 
unconscious  movements.  Still,  stimulation  of  the  Rolandic  area  above 
defined  causes  contraction  of  the  cross-striated  muscles  in  different  parts 
of  the  Vjody. 

The  motor  area  of  each  side  of  the  ])rain  represents  the  muscles  of  the 
other  side  of  the  body,  for  a  large  proportion  (90  per  cent.)  of  the  eft'erent 
paths  that  run  thence  cross  to  the  opposite  side  in  the  lower  part  of  the 
medulla.  Another  sort  of  reversal  is  present  in  the  Rolandic  motor  area. 
The  higher  in  the  erect  human  body  a  muscular  group  is,  the  lower  in 
general  is  its  center  along  the  lateral  surface  of  the  anterior  central  con- 
volution. The  muscles  of  the  face  are  thus  represented  in  front  of  the 
lower  enfl  of  the  fissure  of  Rolando  and  those  of  the  toes  at  its  upper 
end.  Above  the  centers  for  the  head  muscles  are  those  of  the  neck,  then 
upward  those  of  the  wrist,  arm,  siionldcr,  trunk,  and  hip.  T\w  centers  of 
the  leg  extend  in  reverse  order  thence  to  the  median  longitudinal  fissure, 
on  or  near  which  are  situated  the  motor  nuclei  of  the  toes. 

When  this  region  of  the  cortex  is  stimulated  with  any  suitable  agent, 
a.s,  for  example,  a  weak  alternating  induced  electric  current,  contraction 
takes  place  in  the  corresponding  muscle  or  muscle-group  on  the  other 
side  of  the  body.    If  the  stimulus  be  too  strong  or  continued  too  long. 


FUNCTIOXAL  PARTS  OF  THE  XERVOUS  SYSTEM  71 

the  contractions  become  more  and  more  spasmodic  and  radiate  to  sur- 
rounding muscles,  until,  finally,  general  convulsions,  such  as  one  sees  in 
epilepsy  ("grand  mal"),  occur  and  put  an  end  to  this  demonstration  of 
the  motor  centers.  When  these  overlapping  areas  are  destroyed  in  any 
natural  or  artificial  way,  the  corresponding  muscles  are  paralyzed,  and 
most  often  permanently.  Just  what  occurs  in  this  cortical  region  when 
the  normal  animal  wills  to  make  a  muscular  movement  is  not  definitely 
known.  It  is  likely  that  incoming  messages  from  the  muscles,  joints,  and 
skin  direct  in  someway  the  continued  innervation  of  the  particular 
outward  motor  paths  to  be  employed  in  the  movement,  but  just  how  we 
cannot  say.  Morat  supposes  that  there  is  a  continual  circulation  of  ner- 
vous energy  in  the  sensorimotor  paths  which  store  up  stimuli  for  the 
voluntary  movements.  Of  the  original  stimulus  to  deliberate  movements 
we  know  nothing.  In  this  sense  these  centers  are  not  wholly  motor,  but, 
as  often  called,  sensorimotor.  We  have  thus  already  taken  a  step  here 
toward  considering  the  cortex  essentially  a  network  that  is  actuated  as 
a  unit,  at  least  in  performing  its  motor  functions. 

There  is  one  aspect  of  the  relations  of  the  motor  cortex,  so  called,  to 
muscular  function  which  is  attaining  increased  prominence — namely,  the 
relations  of  the  flexor  movements  to  the  extensor  movements.  There 
is  evidently  a  basal  contrast  between  these  sorts  of  movements  related  not 
only  to  the  method  of  balance  in  voluntary  control,  but  at  the  foundation 
also  of  emotional  expression.  Flexion  is  more  characteristic  of  the 
unpleasant  emotions,  while  extensor  movements  are  common  in  pleasant 
emotions.  This  contrast  appears  to  be  far-reaching,  involving  perhaps 
the  whole  matter  of  inhibition.  Thus,  W^edensky,  in  1897,  saw  in  stimu- 
lation experiments  on  the  motor  cortex  that  excitation,  for  example,  of 
the  motor  center  for  extension  on  one  side  of  the  brain,  augmented  the 
excitability  of  the  flexor  center  of  the  other  hemisphere  and  diminished 
the  excitability  of  the  flexor  center  of  the  same  side  of  the  brain — and 
vice  versa.  Such  a  suggestion  introduces  interesting  possibilities  as  to  the 
complexity  of  the  arrangement  of  the  nuclei  controlling  the  coordination 
of  the  various  muscle-groups.  This  reciprocal  mode  of  action  is  not 
unknown  in  other  parts  of  the  organism  and  in  widely  dift'ering  functions. 
Like  many  other  problems,  this  one  awaits  more  exact  knowledge  as  to 
the  relation  of  the  brain-paths  and  centers. 

The  Sensory  Areas. — The  sensory  areas  of  the  cortex  are  more 
numerous  and  more  extensive  than  are  the  motor  areas.  The  kinesthetic 
sensations,  concerned  with  the  control  of  the  muscles,  as  already  noted, 
are  situated  in  the  posterior  central  convolution  just  behind  the  fissure 
of  Rolando,  in  the  region  posterior  to  this,  and  in  the  anterior  central 
convolution.  These  are  co-extensive  with  the  centers  of  voluntary 
movement.  In  addition,  the  mesial  cortex  seems  to  represent,  in  some 
regions,  these  important  afferent  impulses,  part  of  the  frontal  lobe  and  the 
upper  and  posterior  part  of  the  gyrus  fornicatus  being  also  concerned. 
On  the  lateral  surface  of  the  hemisphere  still  farther  back  is  probably 
the  center  which  controls  the  stereognostic  sense,  by  which  the  limbs, 


72  THE  NERVOUS  SYSTEM 

especially  the  hands,  give  a  sense  of  shape  in  space  -without  help  from 
vision.  Thus  the  whole  middle  and  upper  part  of  the  lateral  aspect  of 
the  hemispheres  seems  to  be  connected  with  the  general  bodily  sensitivity. 
The  somesthetic  areas,  which  may  be  defined  as  those  representing  the 
visceral  and  dermal  sensations  as  well  as  the  sensations  arising  in  the 
muscles  (touch  plus  kinesthesia),  have  not  been  definitely  determined. 
Indeed,  frequent  injuries  to  the  motor  areas,  accompanied  with  no  les- 
sening or  derangement  of  general  sensitivity  (somesthesia),  suggest  that 
the  whole  matter  is  still  indefinite.  AYhen  this  knowledge  is  attained, 
the  workings  of  the  nervous  system  will  become  clear. 

The  cortical  representations  of  the  other  four  of  the  "five  senses" 
("feeling"  has  just  l)een  discussed)  are  somewhat  more  definite.  The 
visual  centers  seem  to  be  on  both  sides  of  the  calcarine  fissure  in  the 
mesial  surface  of  the  occipital  lobe,  and  affect  an  area  in  the  cortex  of 
the  lateral  aspect  of  the  occipital  lobe  in  the  first  convolution.  We  should 
suppose  that  one  ill-defined  region  represented  that  part  of  the  retina, 
the  macula  lutea,  concerned  with  the  ever-changing  focus  of  sight. 
Schafer  (also  Henschenj  thinks  that  this  spot  is  at  the  anterior  end  of  the 
calcarine  fissure  on  the  mesial  surface.  We  should  look  for  another 
center  for  color-vision,  but  so  far  none  has  been  found.  We  might  sup- 
pose that  other  small  regions  were  interested  merely  with  perception  of 
light,  and  that  still  another,  as  Willjrand  suggests,  was  concerned  with  the 
appreciation  of  perspective.  At  present,  however,  the  visual  cortical  area 
cannot  be  thus  divided. 

Schafer  concisely  summarizes  somewhat  as  follows  the  probable  rela- 
tions between  the  cortical  areas  of  both  hemispheres  and  the  retina:  The 
visual  area  of  one  hemisphere  is  connected  with  the  corresponding  lateral 
half  of  both  retinae,  while  the  upper,  lower,  and  intermediate  zones  of  the 
area  represent  the  zones  of  the  corresponding  lateral  halves  of  both  retinae; 
the  focal  point  of  the  area,  located  as  above  defined,  is  connected  with 
more  than  the  corresponding  half  of  the  macula  lutea  of  each  retina. 
Thus,  the  areas  for  the  focus  of  seeing  are  each  concerned  with  both 
fovese  centrales.  This  fact  enables  one  to  understand  why  the  movements 
of  the  two  eyes  in  focusing  on  a  new  point  are  so  perfectly  controlled  and 
also  the  perfection  of  sight  when  this  particular  retinal  region  of  the 
fovea  is  concerned. 

The  auditory  centers  in  man  are  in  the  superior  temporal  gyrus  and 
also  in  the  island  of  Reil  within  the  Sylvian  fissure.  It  is  probable  that 
each  center  represents  both  cochlea^,  for  when  these  areas  of  only  one 
hemisphere  are  tlestroyed  both  ears  are  made  partially  deaf.  The  supe- 
rior temporal  convolution  of  the  left  hemisphere  is  concerned  with  the 
hearing  of  words,  and  the  form  of  aphasia  known  as  word-deafness 
is  associated  with  disturbance  or  removal  of  the  posterior  two-thirds 
fXaunynj  of  this  gyrus.    (See  page  39(5  and  Chapter  XI.) 

The* sound  of  the  speaking  voice  is  heard,  Init  the  words  are  not  recog- 
nizee!, nor  appreciated  as  having  any  meaning.  Thus  the  speech-center 
is  in  the  Ifft  heiMi.sj)h('rc  in  right-hai)(lrd  persons.    It  remains  to  be  learned 


FUNCTIONAL  PARTS  OF  THE  NERVOUS  SYSTEM  73 

where  the  speech-center  is  located  in  children  properly  trained  from  the 
first  in  am))idextcrity. 

The  olfadonj  center  of  the  cortex  in  man  is  on  the  mesial  surface  in 
front  of  and  helow  the  corpus  callosum.  It  is  situated  in  the  uncinate 
convolution,  the  anterior  part  of  the  gyrus  fornicatus,  and  posteriorly 
on  the  base  of  the  frontal  lobe.  In  those  lower  animals  in  which  the 
sense  of  smell  is  more  developed  than  in  man,  there  exist  large  special 
olfactorv  lobes  extending  forward  from  the  hemispheres.  In  many  of 
the  brutes  smell  is  the  sense  which,  next  to  the  kinesthesia,  tells  them 
most  about  their  environment.  In  man  it  is  relatively  unimportant,  for 
vision  and  hearing  (owing  to  the  evolution  of  speech)  have  superseded 
this  sense.  There  appears  to  be  only  a  small  amount  of  neural  crossing 
from  one  side  to  the  other  in  the  case  of  smell. 

The  gustatory  center  also  was  thought  by  Ferrier  to  be  located  in  part 
in  the  anterior  portion  of  the  gyrus  fornicatus  on  the  mesial  cortex 
(Bechterew),  the  first  and  second  gyri.  Smell  and  taste  are  closely 
associated  functionally  in  some  cases  {e.  g.,  in  eating),  and  it  is  likely  that 
this  phenomenon  may  depend  partly  on  the  situation  of  the  gustatory 
center  low  down  on  the  mesial  surface  of  the  temporal  lobe  close  to  (but 
below)  one  of  the  centers  of  smell.  Taste-buds,  however,  have  recently 
been  found  in  the  nose.  In  the  anterior  portion  of  this  temporal  area  in 
the  monkey  and  cat  stimulation  produces  movements  of  the  lips  and 
tongue  such  as  are  naturally  associated  with  tasting  (Ferrier).  Bechterew 
obtained  similar  results  in  dogs  from  a  corresponding  spot  on  the  cortex 
of  the  brain,  and  in  apes  from  the  operculum. 

The  "Association-areas." — The  so-called  association-areas  of  the 
human  cortex  take  up  more  than  two-thirds  of  its  surface.  There  are 
three:  the  frontal  area,  the  parietotemporal  area,  and  the  island  of  Eeil. 
So  far  as  direct  experimental  evidence  goes,  we  know  practically  nothing 
as  to  any  special  sensory  or  motor  fimction  of  these  regions,  for  they 
seem  to  be  inexcitable  by  the  means  which  actively  stimulate  the  motor 
and  sensory  areas  about  them.  Actual  removal  of  these  areas,  under 
the  proper  and  extremely  delicate  conditions  necessary,  produces  propor- 
tional loss  of  mental  faculty.  At  present,  however,  the  particulars  of 
this  loss  cannot  be  given.  Flechsig  cites  cases  which  show  that  loss  in 
the  frontal  areas  is  apt  to  be  accompanied  by  a  lessening  of  the  inhibi- 
tory habits  of  the  individual,  so  that  he  becomes,  like  one  of  the  lower 
animals,  deficient  in  cultural  human  control  over  the  organic  tenden- 
cies. 

The  name  association-areas  implies  that  they  are  the  place  where  the 
functions  of  the  brain  are  associated  by  means  of  nerve-fibers  and  nerve- 
cells.  This  may  be  seen,  for  example,  in  the  loss  of  recognition  exhibited 
by  animals  that  have  had  this  area  removed.  ^Nlunk  calls  it  "soul- 
blindness."  These  "association-areas"  are  the  portions  of  the  cortex 
about  which  least  is  known.  Their  function  is  largely  psychological  and 
of  a  complex  nature,  if  one  may  judge  by  the  facts  concerning  these 
regions  so  far  discovered. 


74  THE  XERVOUS  SYSTEM 

The  Optic  Thalami. — These  large  nuclei  in  the  middle  of  each  hemi- 
sphere have  shown  in  experiments  and  in  natural  lesions  so  large  a  variety 
of  apparent  functions  that  to  name  their  general  purpose  or  purposes 
in  the  nervous  system  is  at  present  impossible.  They  seem  to  be  centers 
of  correlation  between  afferent  impulses  and  those  which  produce  move- 
ment. Perhaps,  as  their  name  implies,  vision  is  especially  concerned,  for 
they  are  in  the  nature  of  nerve-currents  passing  from  the  eyes  to  the 
nerve-centers  in  the  occipital  lobes,  and  when  an  eye  is  destroyed  the 
thalamus  of  the  opposite  side  degenerates  somewhat.  Lesions  in  these 
nuclei  produce  undoubtedly  a  rise  of  body-temperature.  They  also- dis- 
turb severely  emotional  expression.  Thus,  in  one  case  a  man  who  was 
found  after  death  to  have  a  large  tumor  of  one  thalamus  could  imitate 
a  smile  perfectly  well  (by  using  probably  his  voluntary  motor  cortex), 
but  on  hearing  anything  humorous  that  side  of  his  face  opposite  to  the 
tumor  remained  blank,  although  the  other  side  of  his  face  smiled  natur- 
allv.  Such  cases  prove  that  one  of  the  functions  of  the  thalami  is  coor- 
dination in  the  muscular  expression  of  the  emotions.  These  nuclei  inter- 
vene between  the  incoming  afferent  impulses  and  the  cortex  of  the  brain 
around  them,  but  exactly  what  they  do  to  these  impulses  is  not  yet  fully 
understood. 

The  Corpora  Striata. — These  consist  of  tw^o  parts:  The  lenticular 
nucleus  and  the  caudate  nucleus.  Lines  of  white  fibers  extend  through 
the  gray  mass  of  the  corpus  (giving  it  its  name).  Little  is  known  about 
the  function  of  these  bodies,  less  than  about  any  other  part  of  the  brain. 
Stimulation  of  one  mechanically  or  electrically  causes  convulsions  of  the 
muscles  on  the  opposite  side  of  the  body,  while  destruction  of  one  corpus 
gives  rise  to  paralysis  of  these  muscles.  This  paralysis  appears  to  be 
transitory  if  only  the  gray  part  of  the  organ  is  destroyed.  Several  experi- 
menters have  seen  a  rise  of  body-temperature  follow^  irritation  of  the  gray 
matter,  but  this  follows  also  from  stimulation  of  various  regions  of  the 
cortex  cerebri.  The  fact,  how^ever,  is  suggestive  of  a  possibility  that  the 
corpora  striata  may  be  concerned  in  the  regulation  of  the  muscular 
metabolism,  and  this  largely  determines  the  heat-production  of  the  body. 

Xothnagel  and  Rezek  have  recently  corroborated  the  conclusions  of 
Magendie  that  the  corpora  striata  are  organs  concerned  in  the  reflex 
coordination  of  the  muscles  of  locomotion.  Destruction  of  part  of  the 
caudate  nucleus  causes  ral)bits  to  go  in  circles  rather  than  straight  ahead. 
This  part  of  the  nucleus  Xothnagel  names  the  nodus  cursorius. 

The  Corpora  Quadrigemina. — ^l^'hese  are  in  the  roof  of  the  aqueduct  of 
Svlvius,  above  the  cerebellum,  and  in  front  of  tlie  lower  posterior  part  of 
the  corpus  callosum.  They  are  composed  of  white  fil)ers  outside  and  of 
gray  matter  within.  Two  of  the  four  small  bodies  are  anterior  and  two 
posterior.  They  apparently  differ  much  in  function.  Through  the  ante- 
rior pair  the  internal  capsule  is  connected  with  the  optic  tract  from  the 
retina  to  the  occipital  lobe,  while  similarly  the  posterior  pair  connects  the 
internal  capsule  with  the  paths  between  the  cochlea  and  temporosphe- 
noidal  cortex.     Monakow  showed   the  connection  (A'  the  cortex  of  the 


FUNCTIOXAL  PARTS  OF  THE  NERVOUS  SYSTEM 


/•> 


Fig.   41 


temporal  lobe  with  the  posterior  body.    They  seem  to  be  unconnected 
with  the  afferent  fibers  of  tlie  eortl. 

It  is  possible  that  the  anterior  corpora  are  concerned  in  regulating  the 
movements  of  the  body  and  of  the  eyes  under  the  influence  of  vision. 
The  posterior  pair  have  probably  some  sort  of  control  over  the  muscular 
movements  of  producing  the  voice. 
On  reniovino;  them  from  dogs  and 
apes  the  voice  is  lost,  and  when 
one  of  them  in  man  is  diseased  the 
hearing  of  the  contralateral  ear 
is  lessened.  Removal  of  the  four 
causes  the  interesting  "forced 
movements"  in  which  the  animal 
on  attempting  to  move  makes 
various  sorts  of  circular  motions 
or  rolls  over.  This  indicates  that 
the  function  of  ecjuilibrium  is  in- 
volved, and  we  know  that  their 
connection  with  the  cerebellum  is 
intimate. 

TheHypophysis Cerebri  (pineal 
body)  is  discussed  under  the  In- 
ternal wSecretions  on  page  218. 

The  Pons. — ^The  pons,  as  its 
name  and  position  both  imply, 
is  primarily  a  bridge  connecting 
by  its  gray  and  its  white  nueral 
structures  the  different  parts  of 
the  nervous  system,  coordinating 
the  sensory  and  the  motor  tracts, 
and  furthering  generally  the  asso- 
ciation of  impulses  of  many  sorts. 
The  sense-organs  of  the  skin  and 
mucous  membranes  send  impidses 
into  the  pons,  as  do  also  those 
of  the  muscles  and  joints.  It 
seems  especially  to  connect  the 
cortex  of  the  hemisphere  with  that 
of  the  opposite  side  of  the  cere- 
bellum, its  middle  portions  lat- 
erally being  the  great  middle 
peduncles  of  the  cerebellum.  With 
the  equilibrium  of  the  head  fand  thereby  of  the  body)  it  has  much  to  do 
by  its  connection  with  the  vestibular  branch  of  the  auditory  nerve  and 
with  the  cerebellum.  The  muscular  movements  of  that  part  of  the  ali- 
mentary canal  within  and  above  the  pharynx  appear  to  be  controlled 
via  the  fifth  nerve  partly  within   the   pons.      Efferent   (muscular    and 


V^entral  (anterior)  aspect  of  tlie  medulla  and 
of  the  parts  above  it:  1,  infundibulum;  2,  tuber 
einereum;  3,  corpora  albicantia;  4,  cerebral 
peduncle;  5,  annular  tubercle;  6,  place  of  origin 
of  the  middle  cerebellar  peduncle;  7,  anterior 
pyramids  of  the  bulb;  8,  decussation  of  these 
pyramids;  9,  olivary  bodies;  10,  restiform  bodie?;; 
11,  arciform  fibers;  12,  upper  end  of  the  spinal 
cord;  13,  denticulate  ligament;  14,  the  cord's 
dura  mater;  15,  optic  tracts;  16,  chiasma;  17, 
motor  oculi  ner\-e;  18,  pathetic;  19,  trigeminal; 
20,  abducens;  21,  facial;  22,  auditory,  etc.;  23, 
ner\'e  of  Wrisberg;  24,  glossopharyngeal;  25, 
pneumogastric;  26,  spinal  accessory;  27,  hypo- 
glossal;   28,  29,  30,  spinal  nerves.      (Sappey.) 


76  THE  NERVOUS  SYSTEM 

glandular)  impulses  may  pass  from  the  gray  nuclei  of  the  organ  to  many 
parts  of  the  body  besides  the  head  by  way  of  the  closely  connected 
medulla  below  and  the  internal  capsule  above. 

The  Medulla  Oblongata. — ^The  medulla  oblongata,  or  bulb,  as  it  is 
sometimes  called,  is  understood  as  compared  with  the  nuclei  just  above 
it  on  the  base  of  the  brain,  though  the  actual  details  of  the  structure  and 
functions  of  the  medulla  are,  however,  not  well  known.  In  general,  the 
medulla  is  largely  a  conducting  organ,  with  many  small,  but  important 
"centers"  (neuronal  regions)  scattered  in  the  interior  of  its  8  or  9  c.c. 
It  gives  rise  to  seven  or  eight  of  the  twelve  so-called  cranial  nerves 
(page  88). 

The  white  matter  of  the  medulla  is  arranged  in  four  bundles  or  columns 
— namely,  the  anterior  pyramid,  the  lateral  tract,  the  restiform  body, 
and  the  posterior  pyramid — on  each  side. 

The  anterior  pyrarnid  is  composed  of  fibers  extending  upward  from  the 
direct  pj-ramidal  tract  of  the  spinal  cord  and  from  the  crossed  pjTamidal 
tract.  Some  of  these  continue  upward  into  the  crus  of  the  cerebrum, 
others  are  lost  in  the  pons,  while  still  others  pass  to  the  cerebellum  as  part 
of  the  restiform  bundle.  In  a  similar  way  the  lateral  tract,  continuous 
below  with  the  lateral  column  of  the  cord,  divides  itself  between  the 
cerebellum  and  the  cerebrum,  joining  partly  with  the  anterior  pyramid. 
The  restiform  body  is  made  up  largely  of  fibers  from  part  of  the  posterior 
column  below,  and  having  received  fibers  within  the  medulla  in  a  com- 
plex way,  divides,  part  going  to  the  cerebellum,  and  part  upward  farther 
into  the  hemisphere.  The  posterior  pyramid  comes  upward  also  from  the 
posterior  column  of  the  cord  (Goll's  column)  and  with  a  portion  of  the 
preceding  continues  into  the  cerebrum  as  part  of  the  fasciculi  teretes. 
Near  the  broad  upper  end  of  the  medulla  is  the  olivary  body,  containing 
the  gray  nucleus  called  the  corpus  dentatum,  and  conspicuous  ventrally 
(anteriorly)  on  the  medulla's  surface.  Fibers  from  this  gray  matter  join 
with  part  of  the  anterior  column  to  form  the  olivary  bundle  ascending 
into  the  crus  of  the  hemisphere. 

The  gray  matter  of  the  medulla,  situated  largely  beneath  (i.  e.,  ventral 
or  anterior  to  the  floor  of  the  fourth  ventricle),  performs  two  general 
functions.  It  is  concerned  with  the  cranial  nerves  (which  will  be  mentioned 
later — see  page  88),  as  already  noted,  and  (as  nuclei)  with  important 
reflex  activities.  It  is  because  the  medulla  connects  and  coordinates 
these  two  important  systems  of  nerves  (those  of  special  sense  and  motion 
with  those  of  the  great  reflex  vegetative  movements  of  the  body),  that 
this  jxjrtion  of  the  spinal  cord  is  of  such  unexcelled  usefulness  in  the 
organism.  It  is  from  the  medulla  more  than  from  any  other  part  of  the 
nerve-scheme  that  the  vital  functions  are  controlled  and  made  to  work 
together,  thus  insuring  the  inherent  unity  of  the  individual  animal. 
Such  basal  functions  as  respiration,  nutrition,  circulation,  and  thermo- 
taxis  rlepend  directly  on  the  duties  of  the  medulla.  Here  are  controlled 
the  many  varied  secretions  and  movements  of  the  whole  complex  alimen- 
tary canal,  the  heart's  action,  the  (Jistribution  of  blood,  the  adapted  move- 


Fia.  42 


Diagram  of  the  structure  of  the  cerebellar  cortex:  P,  cells  of  Purkinje;  p.  axones  of  these 
cells  with  returning  collaterals;  Kbz,  basket  cells;  Kb,  baskets  about  the  bodies  of  Purkinje's 
cells;  K,  small  granular  cells  (the  dots  above  being  their  axones  in  cross-section);  GrK,  large 
granular  cells;  m,  small  cells;  Mf,  mossy  fibers;  Gli,  glia  cells;  Gl^,  short-rayed  cells;  Gl^,  long- 
rayed  cells.-     (Largely  from  v.  KoUiker  via,  Szymonowicz  and  MacCallum.) 


78  THE  XERVOUS  SYSTEM 

ments  of  the  thoracic  walls,  and  many  other  functions  the  action  of  which 
demands  this  complex  sort  of  coordinating  control.  These  actions  of  the 
medulla  are  not  only  reflex  like  those  of  the  cord  farther  down  (i.  e., 
dependent  for  action  on  an  immediately  preceding  nervous  stimulus), 
but  to  a  greater  degree  than  elsewhere  (especially  as  concerns  respiration); 
the  activity  here  is  "automatic,"  that  is,  subject  to  stimuli  not  coming 
from  afar  over  a  nerve,  but  acting  on  the  central  nerve-cells  directly. 
Thus,  the  term  autochthonic  is  more  exact  and  probably  less  misleading 
than  is  "automatic,"  for  it  implies  that  the  actuation  comes  from  the 
immediate  environment  of  the  cell,  a  theory  quite  in  line  with  the  most 
advanced  ideas  of  tissue-metabolism.  In  point  of  fact,  stimuli  which 
actuate  automatic  centers  are  the  physicochemical  conditions  of  the 
blood  flowing  through  the  gray  matter  of  the  medulla. 

Some  of  the  medullary  centers  are  more  reflex  than  autochthonic.  For 
example,  those  of  vomiting,  swallowing,  sneezing,  coughing,  sucking, 
eye  and  mouth  movements,  as  well  as  those  centers  which  control  the 
secretion  of  sweat,  saliva,  and  of  the  numerous  other  digestive  juices 
found  within  the  alimentary  canal,  are  of  this  reflex  nature.  In  brute 
animals  there  is  also  in  the  medulla  a  reflex  center  which  actuates  the 
muscles  productive  of  vocal  sounds.  Most  of  the  centers  so  far  named 
produce  their  eflects  over  the  complicated  cranial  nerves. 

As  essential  as  the  foregoing  functions  are  those  which  follow;  they 
too  are  directed  by  "automatically  acting"  medullary  centers:  inspira- 
tion, expiration,  cardio-inhibition,  cardio-augmentation,  vasoconstric- 
tion, vasodilatation,  and  thermotaxis.  Heubel,  Xothnagel,  and  others 
have  called  attention  to  a  spot  at  the  extreme  upper  end  of  the  medulla 
the  chemical  stimulation  of  which  gives  rise  to  the  universal  muscular 
spasms  such  as  are  seen  in  the  grand  mal  of  epilepsy.  What  the  function 
of  this  arrangement  of  motor  nerve-cells  may  be  it  is  difficult  to  say;  it 
may  be  related  to  the  thermotactic  center  and  be  concerned  in  regulating 
the  metabolic  activity  of  the  muscles  short  of  their  actual  gross  shortening 
by  contraction.  Of  this  kind  of  muscular  action  fibrillary  contraction  is 
an  extreme  degree.  All  these  functions  may  be  set  in  activity  reflexly  as 
well  as  autochthon ically,  for  these  two  modes  in  practice  merge  into 
each  other.  All  of  these,  besides  most  of  the  reflex  centers  proper,  are  of 
necessity  intimately  connected  within  the  gray  tissue  of  the  medulla,  as, 
indeed,  a  brief  consideration  of  their  interrelation  in  the  bodily  functions 
demonstrates. 

The  Cerebellum.-  'i'lic  cerebellum  is  situated  in  man  above  the  over- 
hanging occipital  lobes  of  the  hemispheres  and  dorsal  to  the  pons  and 
the  medulla,  and  consists,  like  the  hemispheres,  of  a  rind  or  cortex  of 
gray  matter  enclosing  white  matter  made  up  of  nerve-fibers.  As  in  the 
case  of  the  cerebral  lobes,  part  of  these  fibers  are  engaged  in  associating 
intimately  all  jjarts  of  the  organ,  while  others  convey  impulses  inward 
to  or  outward  from  the  cerebellum,  connecting  it  most  closely  with  the 
great  conducting  organs  just  described  that  lie  ventrally  to  it.  In  general 
terms,  the  function  of  the  cerebellum  is  to  coordinate  the  muscular  move- 


FUNCTIONAL  PARTS  OF  THE  NERVOUS  SYSTEM 


79 


ments  of  the  body.  It  probably  has  less  to  do  with  sensation  than  any 
other  part  of  the  brain.  Luciani,  indeed,  claims  that  the  cerebellum  may 
be  called  the  organ  of  subconsciousness,  coordinating  the  bodily  func- 
tions independently  of  the  deliberate  will  and  without  the  consciousness 
of  the  individual.  It  may  be  supposed,  then,  that  the  movements  which 
are  directly  under  the  control  of  the  spinal  cord  are  properly  coordinated 

Fig.  43 


Diagram  of  a  human  neural  "segment:"  1,  the  cord's  ventral  (anterior)  median  fissure;  1', 
dorsal  (posterior)  median  fissure;  2,  ventral  root  (efferent  and  perhaps  motor);  3,  dorsal  root 
(afferent  and  perhaps  sensory);  4,  spinal  ganglion;  5,  trunk  of  the  spinal  nerve;  6,  dorsal  limb 
of  the  same;  7,  ventral  limb  of  the  same;  8,  ramus  communicans;  9,  meningeal  branch;  10, 
sympathetic  ganglion;  11,  lateral  cutaneous  branch;  12,  dorsal  limb,  and  13,  ventral  limb  of  the 
same;  14,  ventral  cutaneous  branch;  15,  medial  limb,  and  16,  lateral  limb  of  the  same.    (Rauber.) 


by  the  cerebellum  with  each  other  and  with  the  multitude  of  influences 
which  come  from  the  cerebrum.  The  function  that  has  long  been 
accorded  to  the  cerebellum  (maintenance  of  the  ecjuilibrium  of  the  body) 
is  only  one  of  many  similar  functions,  for  all  involve  coordination. 

The  Spinal  Cord. — The  spinal  cord  is  the  great  distributing  and  con- 
ducting portion  of  the  nervous  system,  and  is  the  seat  also  of  many 


so  THE  NERVOUS  SYSTEM 

reflexes.  It  extends  from  the  top  of  the  medulla  oblongata  (the  medulla 
is  usually  considered  a  part  of  the  cord),  downward  in  the  canal  of  the 
spinal  column,  to  a  point  opposite  the  body  of  the  second  lumbar  vertebra; 
thence  its  large  sacral  roots  continue  as  the  cauda  ec|uina.  The  cord, 
as  a  whole,  is  cylindrical,  but  there  are  two  prominent  enlargements 
laterally,  one  in  the  cervical  and  the  other  in  the  lumbar  region.  The 
former  swelling  is  due  to  the  presence  of  the  nerves  of  the  arms,  the 
latter  to  those  of  the  legs.  The  cord  is  also  made  up  of  gray  matter  and 
white  matter,  the  former  within  the  latter,  but  passing  outward  through 
it  as  the  anterior  and  the  posterior  roots.  The  gray  matter,  as  seen  on 
cross-section  of  the  cord,  is  shaped  much  like  the  two  extended  wings  of 
a  moth  connected  by  a  narrow  commissure.  In  the  center  of  the  latter  is 
the  canal  of  the  cord,  a  minute  tube  (sometimes  called  the  sixth  ven- 
tricle), lined  with  ciliated  epithelium  (beating  upward)  and  filled  with 
the  cerebrospinal  lymph.  The  posterior  end  of  each  of  these  gray- 
matter  wings  is  relatively  slender  and  long,  and  is  continuous  with  the 
posterior  (afferent)  spinal  roots  extending  outward  through  the  white 
matter.  The  anterior  end  of  each  wing  is  rounded  and  short  and  is  sur- 
rounded by  white  matter  except  where  the  anterior  (efferent)  spinal  roots 
pass  outw^ard.  Thus  these  two  pairs  of  roots  divide  each  half  of  the  cord 
into  three  unequal  columns  called  anterior,  lateral,  and  posterior.  The 
whole  cord  is  nearly  divided  dorsoventrally  by  two  fissures,  the  dorsal 
being  deeper  but  narrower  than  the  ventral  or  anterior  fissure,  and  with- 
out a  commissure  of  white  matter  intervening  between  its  inner  end  and 
the  gray  commissure. 

Conduction. — Let  us  look  in  turn  at  the  three  general  functions  of 
the  cord:  conduction,  distribution  and  collection,  and  reflexion.  The 
cord  is  the  great  highway  between  the  legs  and  the  lower  part  of  the 
trunk  and  the  upper  parts  of  the  central  nervous  system.  Numberless 
impulses  passing  upward  and  downward  between  these  regions  go 
directly  in  the  white  matter,  and  sometimes  without  alteration  or  loss, 
probably,  the  whole  length  of  the  cord.  In  general  terms  those  impulses 
passing  upward  (called  afferent,  centripetal,  or  "sensory")  go  in  the 
posterior  or  dor.sal  parts  of  the  cord,  while  those  that  go  downward 
(efferent,  centrifugal,  or  "motor")  pass  in  some  part  or  other  of  the 
anterior  or  ventral  regions.  Owing  to  this  and  other  far-extended 
divisions  of  labor,  not  only  are  there  present  the  three  gross  columns 
already  noted,  made  accidentally  as  it  were  by  the  roots  passing  through 
the  white  matter,  but  there  are  present  in  each  of  these  numerous  smaller 
bundles  of  fibers.  Only  a  few  of  these,  doubtless,  have  been  located 
without  question  and  named.  The  methods  by  which  these  tracts  have 
been  made  out  (they  nee<l  be  only  incntioncd  here)  are  chiefly  four:  by 
emV)ryological  study  of  the  paths,  whieh  develop  at  different  times;  by 
the  observation  of  their  degeneration  when  cut,  away  from  their  trophic 
central  cells;  by  observation  of  yjathological  cases  (tumors,  stabbings, 
etc.);  and  by  direct  vivisectional  experiment  on  animals  similar  to  man. 
How  large  the  number  of  tracts  through  the  white  matter  from  the 
numljerless  fnnctioiifil  regions  of  (lie  body  we  have  as  yet  no  means  of 


FUNCTIONAL  PARTS  OF  THE  NERVOUS  SYSTEM  81 

estimating,  but  they  are  very  numerous.  As  elsewhere  in  anatomical 
nomenclature,  the  (liscoverer's  or  exploiter's  name  is  attached  to  some 
of  the  columns,  but  here,  fortunately,  there  are  other  and  preferable 
names  besides.  In  the  anterior  portion  of  the  cord,  close  to  the  median 
fissure,  is  the  direct  pyramidal  tract  (Turck's),  containing  those  fibers 
leading  from  the  motor  cortex  cerebri  which  do  not  decussate  (cross 
over)  in  the  medulla.  This  extends  downward  only  about  half-way 
through  the  thoracic  cord  because  the  axones  have  been  continually 
giving  off  collaterals  which  cross  to  the  anterior  horn  of  the  opposite  side 
of  the  cord.  Surrounding  this  horn  of  the  gray  matter  is  the  anterior 
association-bundle,  the  so-called  antero-lateral  ground-bundle.  The  fibers 
composing  this  tract  are  not  long  like  those  of  the  preceding  column, 
but  extend  only  a  short  distance  each.  They  are  supposed  to  connect 
cells  of  the  gray  matter.  They  are  the  association-fibers,  in  short,  of  the 
cord.  Some  connect  different  segments  of  the  cord  and  so  have  a  vertical 
course.  Others  are  horizontal  in  direction  and  connect  the  cells  of  the 
anterior  horn  with  the  anterior  nerve-roots  (Starr).  External  to  this 
tract  is  the  narrow  antero-lateral  column  (Lowenthal's)  of  descending 
fibers  coming  in  part  from  the  posterior  bundle  of  the  medulla  and 
probably  from  the  cerebellum.  Yaso-motor  impulses  may  pass  down- 
ward in  this  column  (Starr).  Lateral  to  this  and  on  the  periphery  of  the 
cord  is  the  antero-lateral  column  (Gowers')  of  ascending  fibers,  a  long 
tract  conveying  messages  probably  from  the  cord's  gray  matter  to  the 
cerebellum.  This  column  varies  much  in  shape  in  different  parts  of  the 
cord;  its  fibers  are  more  or  less  confused  with  those  of  the  descending 
column;  it  is  called  also  sometimes  the  anterior  cerebellar  tract.  In  the 
neck  externally  between  these  two  last-named  columns  is  the  bundle  of 
Helweg,  conducting  impulses  apparently  from  the  olivary  body  of  the 
medulla.  Within  the  curve  of  the  lateral  edge  of  the  gray  matter  is 
another  association-column,  the  mixed  lateral  zone  of  short  fibers.  This 
probably  connects  minute  centers  in  the  gray  matter  which,  although 
separated  spatially,  require  close  functional  connection.  Outside  and 
posterior  to  this  ill-understood  zone  is  the  great  crossed  pyramidal  tract 
(Tiirck's).  This  column  is  smaller  and  nearer  the  periphery  farther 
down  in  the  cord  because  of  its  gradual  loss  of  fibers  into  the  gray 
matter  of  the  anterior  horns  and  roots.  The  two  tracts  communicate 
with  each  other  through  the  cord.  It  is  made  up  of  the  90  per  cent,  of 
the  efferent  motor  fibers  from  the  "motor"  cortex  of  the  hemisphere 
which  cross  over  in  the  medulla.  Each  tract,  therefore,  represents  the 
opposite  hemisphere.  In  front  of  this  column  is  a  bundle  called 
Monakoiv's,  which  conducts  impulses  from  the  red  nucleus  of  the  medulla 
to  the  gray  matter  of  the  cord . 

On  the  periphery  of  the  cord  and  external  to  the  column  just  considered 
is  the  direct  cerebellar  tract  (Flechsig's).  The  impulses  which  pass  up 
this  column  (muscle  and  joint  "sensations"  in  part)  arise  more  or  less 
directly  from  the  gray  matter  on  the  outer  side  of  the  posterior  horn 
(Clark's  column)  and  pass  to  the  upper  worm  of  both  sides  of  the  cere- 
bellum by  way  of  the  restiform  body.  This  is  the  vegetative  tract  of 
6 


82  THE  NERVOUS  SYSTEM 

Starr,  so  called  because  up  this  column  pass  the  impulses  coming  from 
the  basal  or  vegetative  organs  of  the  body,  by  which  impulses,  reflexly, 
the  centers  above  control  their  actions.  Posteriorly  lies  the  posterior 
external  column  (Burdach's)  on  the  inner  side  of  the  posterior  horns. 
Some  of  these  hbers  end  about  the  cuneate  nucleus  of  the  medulla. 
They  conduct  tactile  and  muscular  impulses  afferently  from  the  pos- 
terior roots  connected  with  the  arms  and  neck.  Others  are  association- 
fibers  between  various  spinal  segments,  while  others  still,  more  or  less 
horizontal  in  direction,  convey  messages  from  posterior  roots  to  cells  in 
the  gray  matter  of  the  cord.  INIedial  to  this  column  and  bounded  within 
by  the  posterior  fissure  is  the  posterior-median  column  (Goll's)  which 
more  or  less  similarly  conveys  important  (sensory,  afferent)  impulses 
from  the  skin,  muscles,  and  joints  of  the  legs  and  the  lower  part  of  the 
trunk,  upward  to  the  gray  nuclei  of  the  medulla's  nucleus  gracilis.  The 
paths  of  this  tract  communicate  more  or  less  with  the  gray  horn  of  the 
same  side  of  the  cord.  A  distinct  fibrous  septum,  especially  above, 
separates  this  column  from  the  preceding.  On  the  medial  side  of  this 
tract  are  two  smaller  tracts  bordering  on  the  posterior  fissure :  posteriorly 
the  septo-marginal  bundle,  and  just  anterior  to  it,  and  sometimes  extend- 
ing to  the  posterior  commissure,  the  so-called  oval  bundle.  These  are 
probably  association-paths,  as  is  also  the  so-called  comma-tract  (afferent) 
in  the  anterior  part  of  the  posterior  external  column.  Close  to  and 
within  the  place  of  exit  of  the  posterior  roots  from  the  cord  is  the  pos- 
terior marginal  tract  (Lissauer's),  a  small  bundle  composed  of  fibers 
rising  in  the  posterior  horns  and  extending  both  upward  and  downward 
to  connect  with  the  posterior  columns  and  with  other  posterior  roots. 
This,  then,  is  also  an  association-bundle.  It  is  likely  that  in  addition 
to  these  more  or  less  well-defined  tracts  there  are  others  and  especially 
many  small  association-paths.  The  latter  are  particularly  on  the  cord's 
periphery,  and  serve  to  unify  to  an  unknown  extent  all  the  various 
parts  of  the  cord,  as  similar  fibers  unify  the  brain.  The  functional 
facts  demand  this  supposition,  and  many  experiments,  especially  those 
of  Sherrington  and  of  Flechsig,  indicate  strongly  their  existence. 

Distribution  and  Collection. — These  are  together  functions 
general  to  the  spinal  cord,  and  we  have  seen  well  enough  in  the  last 
few  paragraphs  how  they  are  brought  about.  The  cord  has  as  its 
major  part  thick  conducting  columns  composed  of  numberless  fibers 
and  fibrils  wliich  often  run  completely  through  the  trunk  from  end  to 
end.  Witliiii  this  layer  of  white  columns  is  a  mass  of  gray  matter 
composed  in  part  of  nerve-cells  and  of  short  but  complicated  neurones. 
These,  as  we  have  seen,  associate  freely,  by  means  of  their  dendrites, 
neuraxones,  and  countless  collaterals.  Down  the  cord  so  constituted 
come  numberless  and  most  various  impulses,  to  be  distributed  wherever 
normal  function  demands,  l)ut  wlial  (ietermines  just  where,  and  what 
determines  where  not  (Morat  calls  this  viatility),  we  do  not  as  yet 
know.  Tn  like  manner  countless  impulses  ])ass  into  the  cord,  to  be  dis- 
tril)Utcd  in  a  way  more  or  less  similar.  Again,  numerous  influences 
f-ritcr  the  coid  ;iih1  are  made  to  concentrate  or  to  collect  so  that  their 


FUNCTIONAL  PARTS  OF  THE  NERVOUS  SYSTEM  83 

combined  message  goes  in  only  one  direction,  perhaps  to  one  region  for 
the  performance  perhaps  of  a  single  end.  How  all  these  things  are 
done  in  particular  we  do  not  know,  but  we  see  well-nigh  universal 
interconnection,  and  we  observe  continually  the  results  in  living  animals 
of  these  processes  of  adapted  collection  and  distribution  by  the  long  and 
complicated  spinal  cord.  This  viatilityof  the  nerve-centers  is  one  of  the 
functional  marvels  of  biology. 

Reflexion,  or  Reflex  Action. — Reflexes  are  actions  of  the  body 
carried  on  by  the  spinal  cord  (and  perhaps  by  the  cerebellum)  without 
the  immediate  volition  or  even  knowledge  of  the  individual.  In  a  typical 
reflex  action,  as  the  name  implies,  there  is  a  turning-backward  of  the 
nerve-current.  The  impulse  originates  in  some  sense-organ,  passes 
through  some  nerve-cell  or  nerve-cells,  and  goes  out  of  the  central 
nervous  system  to  the  muscle  or  gland,  or  possibly  to  exert  trophic 
action  on  some  portion  of  the  tissue.  The  influence  which  passes  from 
the  sense-organ  to  the  central  nerve-organ  is  called  the  afferent  or 
centripetal  impulse.  Its  passage  through  the  gray  matter  is  called  the 
central  process.  It  should  not  be  thought  that  the  afferent  sense-organ 
must  be  on  the  periphery  of  the  body  or  that  the  efferent  instrument 
(muscle  or  gland  usually),  must  be  far  away  from  the  reflecting  center, 
because  the  impulse  might  and  often  does  originate  very  close  to  or 
even  within  the  spinal  column  and  pass  to  a  muscle  cell  or  gland 
alveolus  close  by.  The  terms  afferent  and  efferent  were  derived  from 
typical  instances  of  reflex  action,  such  as  occurs  when  a  touch  on  the 
foot,  for  example,  causes  it  to  be  withdrawn.  The  central  process, 
properly  speaking,  does  not  have  to  be  in  the  spinal  cord,  but  may 
occur  in  one  of  the  numerous  gray  nuclei  elsewhere  in  the  body. 
Matters  are  so  complicated  in  nerve-action  that  seldom  are  processes 
limited  to  that  wdiich  their  names  denote. 

In  general  terms,  the  afferent  or  centripetal  impulse  goes  into  the  spinal 
cord  through  the  posterior  roots.  Here  it  is  associated,  mainly  in  the  gray 
alffiof  the  cord,  with  many  other  impulses,  perhaps  passing  up  and  down 
in  connected  neurones.  It  then  passes  out,  properly  adapted  to  its  purpose, 
in  the  anterior  spinal  roots  on  its  way  to  the  muscle  or  the  gland.  Mat- 
ters in  fact,  however,  are  very  much  more  complicated  than  such  a 
mere  formula  implies,  especially  as  regards  the  association  which 
abounds  in  the  gray  matter.  The  greatest  mystery  concerned  with  the 
reflex  movements  of  the  body  is  as  to  how  the  necessary  distribution 
and  selection  of  paths  (viatility)  is  made.  A  single  unexpected  touch, 
for  example,  on  the  back  of  the  neck  causes  the  exactly  adapted  and  co- 
ordinated contraction  of  scores  of  complicated  muscles  of  the  trunk,  neck, 
and  legs.  The  centers  in  the  cord,  consisting  of  knots  of  neurones,  are 
somehow  able  to  distribute  an  impulse  among  the  neurones  so  as  to 
make  the  succeeding  act  exactly  the  one  out  of  possible  thousands  which 
is  most  useful  to  the  animal.  This  is  the  great  mystery  about  all  neuro- 
muscular actions,  and  when  the  problem  is  complicated  by  trying  to 
imagine  how  the  influences  from  the  brain  above  are  connected  with  those 
proper  to  the  spinal  cord,  the   problem  is  obviously  a  most  complicated 


84  THE  XERVOUS  SYSTEM 

one.  The  facts  are  comparatively  simple;  it  is  only  how  they  are  accom- 
plishetl  that  physiology  does  not  as  yet  explain.  There  are  thousands 
of  unitary  muscular  bundles  whose  arithmetic  combination  w^ould  make 
millions  of  possibilities  of  action.  There  are,  too,  thousands  of  pos- 
sible outgoing  nerve-paths  whose  possible  combination  would  make  other 
millions  of  possibilities  of  action.  All  these  millions  combine  in  the 
neuro-muscular  mechanism,  yet  out  of  them  normally  the  one  right  path 
is  chosen ! 

For  the  most  part  reflex  actions  are  conducted  without  much  influence 
from  the  brain,  especially  from  the  cortex,  but  it  appears  certain  that 
impulses  regularly  do  pass  from  the  reflex  spinal  centers  upward  into 
the  brain.  In  general,  it  may  be  said  that  the  cortex  of  the  brain,  during 
waking  hours  at  least,  exerts  a  controlling  influence  over  most  of  the 
reflexes.  Those  movements  are  largely  concerned  with  the  purely  vege- 
tative processes,  such  as  the  movements  of  the  alimentary  canal  and  of 
the  heart.  These  have,  however,  become  so  nearly  "automatic"  that 
in  their  normal  condition  they  occur  quite  without  the  knowledge  of 
the  individual,  the  nerve-impulses  not  being  correlated  with  conscious- 
ness. Still,  it  needs  only  some  inflammation  in  these  parts  or  disturb- 
ance in  their  nervous  mechanisms  to  show  that,  so  far  as  the  nervous 
impulses  are  concerned,  there  is  a  very  close  constant  relation  between 
even  these  organs  and  the  cortex  of  the  brain. 

The  more  highly  developed  the  animal,  the  smaller  the  proportion 
of  his  activity  controlled  by  the  spinal  cord.  In  worms,  for  example^ 
there  is  no  brain  worthy  to  be  called  such,  and  the  animal  is  wholly  a 
"spinal  animal,"  such  as,  for  example,  the  frog  becomes  when  its  fore- 
brain  and  mid-brain  are  destroyed.  In  future  chapters  we  shall  discuss 
more  in  detail  the  relations  of  reflex  actions  to  voluntary  actions  and  to 
mental  function  or  consciousness. 

Although  of  many  various  sorts,  the  human  spinal  reflexes  are  not 
very  satisfactorily  classifiable.  We  may  think  of  them,  however,  as  either 
vegetative  or  non-vegetative,  although  every  normal  reflex  has  more  or 
less  of  a  vegetative  or  basal  value  to  the  organism.  For  convenience, 
however,  we  may  arrange  the  spinal  reflex-actions,  including  those  of 
the  medulla,  in  these  two  classes.  The  former  class,  vec/etative  reflexions^ 
includes  those  which  are  essential  to  the  life  of  the  organism.  Among 
them  are  inspiration,  expiration,  sneezing,  coughing,  cardio-inhibition, 
cardio-augmentation,  vaso-dilation,  vaso-constriction,  thermogenesis, 
thermolysis,  sucking,  mammillary  erection, mastication,  salivation,  deglu- 
tition, digestive  secretion,  digestive  motion,  vomiting,  sweating,  urination, 
copulation,  erection,  ejaculation,  parturition,  winking,  and  pupillary 
motion.  The  non-vegciative  reflexes  are  ver\^  numerous  if  we  include 
many  actions  which  merge  indistinguishably  into  voluntary  movements. 
These  are  such  actions  as  movements  of  self-defence,  of  withdrawal  from 
injury,  walking,  runm'ng,  swimming,  and  speaking.  Included  in  this 
class  are  a  number  of  skin-reflexes,  the  so-called  superficial  spinal  re- 
flexes: the  gluteal,  plantar,  cremasteric,  epigastric,  abdominal,  and 
.scapular  reflexes.     These  are  of  much  practical  use  to  neurologists  and 


FUXCTIOXAL  PARTS  OF  THE  XERVOUS  SYSTEM  85 

surgeons  in  determining  especially  the  upper  limits  of  spinal-cord  lesions. 
Some  of  these  reflexes  have  concern  only  witli  a  small  knot  of  neurones 
in  the  medulla  oblon<fata  or  with  cells  in  one  spinal  segment,  while  others 
involve  neurones  scattered  far  up  and  down  the  cord  through  many 
segments  and  by  multitudes  of  cells  and  pathways.  Their  two  common 
aspects  are  that  their  centers  are  located  in  some  part  of  the  spinal  cord, 
including  the  medulla;  and  that  they  are  in  some  degree  slightly  or 
wholly  controlled  by  afferent  impulses  coming  from  a  less  or  a  greater 
distance. 

We  quote  from  Hall  the  following  table,  showing  the  location  in  the 
spinal  cord  of  forty-three  reflexes.  It  is  useful  not  only  as  a  summary 
of  the  reflex  functions  of  the  cord,  but  for  diagnostic  purposes  in  many 
diseases  of  the  nervous  system: 

Reflex.  Locatiox  of  Center. 

Plantar 1st  and  2d  sacral  segments. 

Gluteal 4th  and  5th  lumbar. 

Cremasteric 1st  to  .3d  lumbar. 

Erectile  of  penis 1st  and  2d  lumbar. 

Abdominal 7th  to  11th  dorsal. 

Epigastric 4th  to  7th  dorsal. 

Mammary 2d  to  12th  dorsal. 

Scapular 5th  cervical  to  1st  dorsal. 

Palmar 7th  cervical  to  1st  dorsal. 

Laryngeal 10th  cranial  nerve,  bulb. 

Pharyngeal 9th  cranial  nerve,  bulb. 

Nasal 5th  cranial  nerve,  bulb. 

Conjimctival 5th  cranial  nerve,  bulb. 

Tendo-AchiJlis 3d  to  5th  sacral. 

Ankle-clonus 5th  lumbar. 

Patellar 2d  lumbar. 

Extensors  of  hand       ....  6th  cervical. 

Flexors  of  hand 7th  and  8th  cervical. 

Pronator  of  hand 8th  cervical. 

Triceps 6th  cervical. 

Supinator  of  hand        ....  5th  cervical. 

Biceps 4th  and  5th  cervical. 

Inferior  maxillary        ....  5th  cranial  nerve,  bulb. 

Defecation 4th  liunbar. 

Micturition 3d  lumbar. 

Seminal  emission 4th  lumbar  to  3d  sacral. 

Parturition 1st  and  2d  lumbar. 

Intestinal  movements        .      .      .  10th  cranial  ner\e,  bulb. 

Duodenal  regurgitation     .  .  1st  to  4th  dorsal  (splanchnic). 

Pylorus 10th  cranial  nerve,  bulb. 

Gastric  movements      ....  10th  cranial  nerve,  bulb. 

Emesis 10th  cranial  nerve,  bulb. 

Deglutition 9th  and  10th  cranial  nerves,  bulb. 

Sucking 5th,  7th,  and  11th  cranial  nerves,  bulb. 

Respiration Tip  of  calamus  scriptorius,  bulb. 

Expiration 10th  cranial  nerve,  bulb. 

Inspiration 10th  cranial  nerve,  bulb. 

Circulation : 

Cardiac  acceleration       ...  2d  and  3d  et  seq.  dorsal. 

Cardiac  inhibition    ....  10th  cranial  nerve,  bulb. 

Va.so-motor  dilatation,  blush    .  7th  cranial  to  3d  sacral. 

Vaso-motor  constriction,  pallor  2d  dorsal  to  2d  lumbar,  inclusive. 

Pupillary 4th  cervical  to  3d  dorsal. 

Vaso-motor Floor  of  the  4th  ventricle. 

Salivary  secretion        ....  7tli  cranial  nerve,  bulb  (chorda  tympani). 


86  THE  NERVOUS  SYSTEM 

The  brain  can  exert  normally  almost  any  degree  of  inhibitory  control 
over  the  reflex  actions.  It  commonly  acts  in  this  way  provided  it  has  been 
made  aware  that  the  reflex  influences  are  to  pass,  and  provided  also  that 
the  neuro-muscular  mechanism  has  not  passed  by  long-inherited  habit 
into  a  condition  of  practical  atomatism  such  as  is  observed,  for  example, 
in  the  heart  and  intestines.  Inhibition  is  one  of  the  great  problems  of  the 
day  in  physiology;  about  its  cause,  its  actual  mode  of  working,  and  its 
limits  of  influence  we  still  know  but  very  little. 

Coordination. — Coordination  of  movements  is  accomplished  through 
the  meeting  of  the  separate  nerve-paths  in  cells,  in  plexuses,  or  in  the 
"centers"  of  the  central  nervous  system.  According  to  the  neurone- 
theory,  each  fiber  (axone)  being  the  unit  of  conduction,  coordination  can 
scarcely  be  supposetl  to  take  place  within  the  cell,  but  rather  in  the 
groups  of  neurones  called  centers.  Various  kinds  of  centers  have  been 
already  described.  If,  however,  we  consider  the  fibril  within  the 
fiber  as  the  conducting  unit,  we  might  suppose  that  the  various 
impulses  coming  in  over  the  hundreds  of  fibrils  may  be  arranged  and 
connected  within  the  body  of  the  cell,  the  better  to  serve  the  various 
actions  of  muscles,  the  secretion  of  glands,  the  functions  of  the  sense- 
organs,  or  other  functions.  We  cannot  as  yet  decide  between  these 
opposed  points  of  view  of  the  nervous  system  because  of  the  histological 
uncertainty. 

In  its  function  of  unifying  the  different  actions  of  the  body,  the 
coordinating  process  is  essential,  as  is  readily  seen  from  any  one  of 
numerous  complex  muscular  acts.  Take,  for  example,  speech.  (See 
page  394.)  This  complicated  process  in  its  mechanical  aspects  is  essen- 
tially produced  by  draughts  of  air  to  and  from  the  lungs  which  cause 
vibration  of  the  vocal  cords,  while  the  throat,  tongue,  lips,  teeth,  etc., 
are  adapted  at  the  same  time  to  the  requirements  of  word-enunciation. 
To  produce  the  requisite  draughts  of  air  the  whole  respiratory  muscular- 
mechansim  has  to  act  in  an  exactly  suitable  way,  inspiration  and  expira- 
tion being  carefully  adapted  in  force,  frequency,  and  continuance  to 
the  exact  needs.  This  means  not  only  numerous  afferent  impulses 
passing  continually  to  the  speech-center  in  the  temporal  lobe  of  the 
brain,  but  hundrecJsand  probably  thousands  of  efferent  impulses  passing 
thence  indirectly  (by  way  of  the  respiratory  center)  to  the  numerous 
muscles  of  respiration.  None  of  these  cross-striated  muscles  and  no 
portion  of  any  will  work  by  itself,  but  every  part  must  be  directed  in 
exactly  the  proper  way  to  produce  the  precise  movements  demanded  of 
them.  Similarly  in  the  larynx,  numerous  small  muscles  must  be  made 
to  act  together  as  they  have  acted  in  producing  similar  sounds  since 
the  individual  learned  to  talk.  This  mechanism  is  by  itself  one  of  the 
most  complex  of  muscular  coordinations.  The  soft  palate  must  be 
innervated  in  a  certain  way,  and  the  tongue  must  be  made  to  select 
out  of  its  multitude  of  movements  just  those,  and  none  others,  required 
for  the  particular  words  expressed.  The  lips  take  part  also  and  involve 
exactly  the  right  innervation  of  many  small  muscles,  while  the  muscles 


CERTAIN  SETS  OF  NERVES  ■    87 

of  the  jaw  must  at  the  same  time  so  act  as  to  make  use  both  of  the  mouth 
and  the  teeth  in  the  one  proper  manner.  All  of  these  parts  meanwhile 
are  sending  inward  to  the  hrain  and  spinal  cord  a  continual  stream  of 
afl'erent,  sensory  (kinesthetic)  impulses  by  which  alone  the  centers  can 
guide  the  muscles  to  contract  to  the  requisite  extent.  The  mental  aspects 
of  speech  (the  one  human  function)  require  a  multitude  of  other  impulses 
of  which  we  know  essentially  nothing.  Thus  complicated  is  the  func- 
tion of  nervous  coordination  going  on  continually  all  over  the  body 
for  hundreds  of  complex  acts.  The  details  of  the  nervous  currents 
cannot  be  made  out  in  any  case,  but  the  principle  is  now  sufficiently 
clear. 

In  the  illustration  just  given  there  is  one  dominant  center,  that  of 
speech,  but  it  exerts  control  over  a  number  of  coordinating  centers  cor- 
responding to  the  organs  employed  in  the  act.  Besides  the  respiratory 
center,  that  of  the  tongue  is  regulated  and  that  portion  of  the  nervous 
system  directing  mastication,  in  itself  a  complicated  act.  In  the  process 
of  swallowing  nearly  the  same  organs  (save  in  part  for  the  larynx)  are 
involved.  The  movements  of  each  are  then  different,  however,  and  the 
center  of  deglutition  is  the  dominant  center  while  that  of  speech  is 
affected  in  part  only  as  subsidiary. 

Thus  continually  all  through  the  body  a  vast  but  exactly  ordered  mul- 
titude of  impulses  is  passing  to  and  fro  between  all  the  parts.  The  com- 
plexity of  these  groups  of  influences  along  nerves  cannot  be  even  imagined 
unless  one  impresses  on  his  mind  the  number  and  the  variety  of  interests 
and  of  purposes  of  the  body's  sense-organs  and  of  its  muscular  and  gland- 
ular and  metabolic  units.  Uncoordinated  these  would  make  a  chaos, 
but  coordinated  by  the  nervous  system  they  are  the  essential  part  of  a 
living  animal  body. 

CERTAIN  SETS  OF  NERVES. 

Forty-three  pairs  of  nerves  connect  the  body-tissues  of  man  with  his 
central  nervous  system,  one  of  each  pair  going  outward  on  each  side. 
Twelve  of  these  pairs  arise  from  the  base  of  the  brain  and  the  medulla 
oblongata;  these  are  called,  therefore,  cranial  nerves.  The  other  thirty- 
one  pairs  arise  from  the  various  segments  of  the  cord ;  these  are  hence 
known  as  spinal  nerves.  Besides  these,  numerous  sets  of  ganglia  and 
nerves  exist  in  the  body  and  perform  various  vegetative  functions ;  these 
ganglia  and  nerves  are  (but  none  too  well)  termed  the  sympathetic 
"system,"  as  if  they  in  some  w^ay  were  distinct  from  the  rest  of  the 
nervous  system.  This,  of  course,  they  are  not,  but  rather  an  important 
portion  of  the  common  neural  fabric  and  very  intimately  related  to  all 
its  parts  in  many  ways.  If  we  speak  of  these  three  "sets"  of  nerves 
as  separate,  it  is  only  for  convenience  and  because  they  have  been  thus 
unduly  and  arbitrarily  separated  in  anatomical  treatises  for  many  years 
and  have  so  in  a  sense  really  become  to  the  science  sets  of  nerves. 
Functionally,  however,  it  must  be  continually  remembered  they  are  only 


88  THE  NERVOUS  SYSTEM 

to  a  verv  limited  degree  separated  from  the  rest  and  are  combined  with 
it  to  form  the  unity  of  the  organism.  We  describe  them  separately, 
but  in  life  these  three  sets  of  nerves  act  invariably  more  or  less  together. 
These  same  considerations  are  true  also  of  the  "separate"  nerves — 
separate  only  anatomically. 

Fig.  44 


I.  olf. 

77.  opt. 
III.  ocm. 

IV.  trocli. 
V.  tr(j. 

ri.  aid. 

VII.  fac. 

VIII.  acust. 

IX.  glossph. 

X.  vag. 

XI.  access. 

XII.  Jm¥ 


The  base  of  the  brain,  showing  especially  the  apparent  origins  of  the  cranial  ner\-es:  I-XII, 
the  respective  cranial  nerves;  .IR,  island  of  Reil;  h,  hypophysis  cerebri;  th,  optic  thalamus;  cc, 
corpora  albicantia;  (jm,  mesial  geniculate  body;  gl,  lateral  geniculate  body;  py,  pyramid;  ov, 
olivary  body;   C'Fl,  first  spinal  ner\'e  (cervical).      (Schwalbe.) 


The  Cranial  Nerves. — These  are  twelve  in  number  in  each  side  of  the 
body.  They  are  known  by  their  respective  names,  but  often,  especially 
in  the  newer  books,  also  by  numerals,  according  to  this  list: 


Olfactof}-,  or  first. 
Optic,  or  .second. 
Motor  ociili,  or  third. 
Pathetic,  or  fourth. 
Trigeminal,  or  filth. 
Abducens,  or  sixth. 


Facial,  or  seventh. 
Auditory,  or  eijihth. 
Glosso-pharyngcal,  or  nintli. 
Vagus  (pneumogastric),  or  tenth 
Spinal  accessory,  or  eleventh. 
Hypoglossal,  or  twelfth. 


PLATE    III 


Topography  of  the  Cranial  Nerve-nuclei  of  the  Floor  of  the 
Fourth   Ventricle.     (Morat.) 

The  efferent  nuclei  are  in  red  and  the  afferent  nuclei  in  blue. 


CERTAIX  SETS  OF  XERVES 


89 


Of  these,  three,  tlie  olfactory,  optic,  and  auditorv,  are  (mostly 
afferent)  nerves  of  special  sense;  five,  the  motor  oculi,  pathetic,  ab- 
ducens,  facial,  and  hypoglossal,  are  chiefly  efferent  or  motor  nerves; 
while  the  remaining  four,  the  trigeminal,  glosso-pharyngeal,  vagus,  and 
spinal  accessory,  are  of  mixed  functions — special  sense,  general  sensibility, 
(touch,  pain,  myesthesia,  heat,  cold,  etc.),  trophism,  motion,  and  vaso- 
motion  in  various  combinations,  whose  details  are  not  yet  in  all  cases 
sure.  For  detailed  information  as  to  the  cerebral  origins,  the  distribu- 
tion, and  Xhe  functions  of  these  complex  groups  of  afferent  and  efferent 
nerve-paths  the  reader  is  referred  to  text-books  of  anatomy  and  of  the 
physiology  of  the  nervous  system. 


Fig.  45 

v—" - 


-  Brain 


—  Cerebellum 


Seruory  root 


•Fibre  of  ass. 


Muaoui.  bundl« 


Diagram  shovi-ing  the  collection  of  different  sorts  of  influence  by  a  motor  root  nerve-cell. 

(Morat.) 


The  Spinal  Nerves. — These  are  thirty-one  in  number,  on  either  side 
of  the  body.  Each  arises  by  two  roots,  an  anterior  and  a  posterior. 
The  former  root  is  mostly  motor,  vaso-dilator,  "secretory,"  and 
"trophic";  the  latter  mostly  sensory.  Each  divides  into  two  trunks,  one 
leading  to  the  tissues  of  the  back,  and  the  other,  much  the  larger,  to  the 
remaining  parts  of  the  bofly-trunk  and  to  the  limbs.  We  need  do  no  more 
than  to  explain  some  of  the  principles  of  action  of  these  afferent,  inward, 
and  efferent,  outward,  impulses  and  to  summarize  for  reference  purposes 
the  basis  of  distribution  of  the  motor  nerves,  showing  the  sensory  dis- 
tribution so  far  as  it  is  dermal  by  an  illustration.    The  process  here  out- 


90 


THE  NERVOUS  SYSTEM 


lined  is  on  the  basis  of  the  neurone  theory;  should  the  nerve-cells  be 
proved  to  be  only  trophic  centers,  material  changes  would  of  necessity 
result  in  our  notions  as  to  the  mode  of  action  of  the  spinal  cord  and 
especially  regarding  its  relations  to  the  spinal  nerves. 

The  anterior  roots,  mostly  efferent  in  action,  receive  their  impulses  from 
many-branched  neurones  situated  in  the  gray  matter  of  the  cord,  and 
more  usually  in  the  anterior  (ventral)  horns  of  this  gray  matter.  In  the 
most  complex  animals  each  ventral  root  is  made  up  by  combination  of  a 
row  of  rootlets,  and  each  rootlet  represents  in  miniature  the  whole  root, 
the  spinal  cells  in  connection  with  them  coming  from  slightly  different 
levels  of  the  cord.  By  this  arrangement  it  is  brought  about  that  no  root 
or  rootlet  represents  a  single  muscle,  but  rather  in  part  all  the  muscles  of 
a  functional  group.     Each  muscle,  moreover,  is  thus  innervated  from 


Posterior  root, 
a    b    c 


Fig.  46 

Posterior 
median  Column  Posterior  Colum,n  of 
septum,  of  Goll.    column.     Burdach. 


Posterior 
horn. 


Anterior  ground 
\  bundle. 

Direct  pyramidal 
column  (Turck). 


_  Direct  cerebellar 

column. 

Crossed  pyram- 
"idal  colum,n. 

Column  of 
Clark. 

Mixed  lateral 
column. 

Ascending  antero- 
lateral column 
(Gowers). 
Anterior  com- 
missure. 

Descending  ante- 
rolateral area. 


Diagram  of  the  physiological  structure  of  the  spinal  cord. 

and  H.  Hackei.) 


(Ziehen,  von  Bardeleben, 


several  (three  or  four)  segments.  In  some  parts  of  the  cord,  notably  those 
representing  the  neck-  and  limb-muscles,  the  anterior  root-cells  are  dis- 
tinctly collected  into  groups,  each  group  probably  innervating  collectively 
a  group  of  muscles.  The  largest  motor  cells  probably  control  cross- 
striated  (skeletal)  muscles,  while  the  smaller  ones  may  innervate  the 
muscle-fibers  ("unstriate<l")  of  the  bloodvessels  and  of  the  viscera. 
Cells  for  flexion  and  cells  for  extension  of  a  joint,  for  example,  seem  to 
lie  intermingle<l  in  the  same  segments  of  gray  matter.  Both  sorts  of 
cells  are  probably  (Sherrington)  actuated  at  every  movement  of  the  joint, 
flexor  or  extensor,  one  set  l)eing  stimulated  to  actuate  and  the  other  to 
inhibit.  Sherrington  notes  the  discovery  by  Golgi  that  from  the  neur- 
axones  of  some  spinal  efl'erent  root-cells  "side-fibers"  are  given  near  their 
origins.  These  may  conduct  efl'erently  into  the  axone,  but  for  what 
purpose  is  not  known;  von  Lenhossek  terms  them  axo-d  end  rites. 


CERTAIN  SETS  OF  NERVES  91 

The  functions  of  the  impulses  passing  in  the  anterior  roots  are  various 
but  not  yet  definitely  understood.  Most  conspicuous  is  their  function 
of  controlling  the  cross-striated  muscles  of  the  body,  these  impulses  being 
perhaps  of  two  phases,  actuating  and  inhibitory.  The  starting-point  of 
these  influences  is  probably  in  the  cortex  of  the  hemispheres  anterior  to 
the  Rolandic  fissure.  These  impulses,  then,  are  productive  of  voluntary 
or  deliberate  movements.  It  is  possible  that  many  of  these  impulses 
start  in  the  cerebellar  cortex.  In  the  case  of  reflexions,  the  incitement 
of  the  motor  neurones  comes  from  other  neurones  interlacing  with  them 
and  thereby  usually  from  the  periphery.  As  we  have  just  seen,  each 
muscle  is  innervated  by  the  fibers  of  several  roots  and  so  controls  in  part 
a  whole  functional  group  of  muscles,  especially  in  the  hands  and  feet. 
Smooth  muscles  in  the  hollow  viscera  are  in  part  actuated  through  the 
anterior  roots,  notably  those  of  the  uterus,  urinary  bladder,  and  the  skin. 
Another  sort  of  influence  passing  outward  in  the  ventral  roots  is  that  of  vaso- 
motor  action  and  tone,  the  probably  two-phased  influence  which  so  essen- 
tially adapts  the  size  of  the  arteries  to  the  body's  requirements  both  local 
and  general.  One  phase  is  vaso-constrictor  while  the  other  is  vaso-dilator. 
\Miether  the  latter  is  an  inhibitory  influence  on  the  former  or  a  contractile 
effect  is  not  yet  certain.  Impulses  which  bring  about  the  secretion  of 
sweat  pass  out  of  tlje  spinal  cord  in  the  anterior  roots.  This  stimulus  is 
either  secretory  in  the  proper  sense  of  the  term  or  only  an  effect  of  vaso- 
dilatation. Which,  it  is  still  undecided,  largely  because  of  the  slight  his- 
tological doubt  as  to  whether  nerve-fibers  enter  epithelial  cells  in  all 
cases.  Similar  uncertainty  sometimes  exists  about  a  supposed  "tro'phic" 
(chemic?)  influence  exerted  by  the  central  nerve-system.  ^Yhatever  the 
nature  of  this  undoubted  control  (proved  by  a  host  of  pathological  cases 
as. well  as  by  the  phenomena  following  nerve-suturing),  the  ventral, 
anterior,  roots  are  the  paths  of  its  conveyance  outward. 

The  posterior  spinal  roots  (so  far  as  their  nerve-cells  at  present  imply) 
have  their  origin  in  ganglia,  more  or  less  ellipsoidal  in  shape,  to  be  found 
one  on  each  dorsal  root  close  to  its  junction  with  the  ventral  root.  The 
accompanying  diagram  (Fig.  46)  indicates  the  probable  finer  structure  of 
these  ganglia  and  the  relations  of  the  ventral  and  dorsal  fibers  to  them. 
The  afferent,  "sensory,"  nerve-cells  for  the  most  part  have  two  axones. 
Each  of  these  divides  into  two  medullated  branches,  one  having  grown 
from  the  cells  of  the  "neural  crests"  into  the  posterior  horn  of  the  cord's 
gray  matter,  and  the  other  centrifugally  into  the  body's  tissues  and 
periphery.  Some  of  the  ganglion-cells  are  multipolar,  like  those  of  the 
sympathetic,  while  others  are  bipolar,  but  with  short  branching  axones 
which  communicate  (Dogiel)  with  the  other  sort  of  bipolar  cells.  Fibers, 
not  numerous,  from  the  sympathetic  ganglia  communicate  freely  with 
the  cells  of  these  spinal  ganglia.  In  the  cord's  gray  matter  the  den- 
drites of  these  neurones  associate  freely  with  hosts  of  nerve-cells  and 
neurones,  motor  and  sensory,  as  well  as  with  many  of  a  purely 
associative  function  and  position.  Fibers  from  the  ventral  ("sensory") 
root  pass  round  through  the  ganglion  and  centripetally  into  the  anterior 


92 


THE  NERVOUS  SYSTEM 


root.    This  gives  the  so-called  recurrent  sensibility  of  the  anterior  roots 
observed  in  mammals  and  birds;  it  does  not  obtain  in  the  frog. 

For  diagnostic  purposes,  the  following  table  of  the  relations  of  the 
skeletal  muscles  and  the  spinal  anterior  roots  as  compiled  by  Kocher 
from  human  clinical  material  is  of  importance: 


Roots. 
Cervical  I. 

"  II. 

"  III. 

"  IV. 

"  V. 

"       VI. 


"       VII. 

"       VIII. 
Dorsal  I. 
"      I-XII. 
"      I-XI. 
"      VII-XII. 
Liunbar  I. 

"       II. 

"       III. 

"       IV. 

"       V. 


Sacral  I. 


II. 


III. 
IV. 
V. 


Muscles. 

Small  neck-muscles,  sterno-hyoideus,   sterno-thyroideus,  omohy- 

oideus. 
Sterno-cleido-mastoideus,  trapezius. 
Platysma  myoides. 
Scaleni,  diaphragma. 
Rhomboidei,  supra-   and    infra-spinatus,  coraco-brachialis,  biceps, 

brachialis  anticus,  deltoideus,  supinator  longus  and  brevis. 
Subscapularis,  pectorialis  major  and  minor,  pronator  radii  teres, 

pronator    quadratus,   latissinius   dorsi,  teres  major,   triceps, 

serratus  magnus. 
Flexors  and  extensors  of  the  wrist. 
Long  flexors  and  extensors  of  the  fingers. 
All  the  small  muscles  of  the  hand  and  fingers. 
Muscles  of  the  back. 
Intercostals. 

Muscles  of  the  abdomen. 

Lower  abdominal  muscles,  quadratus  lumborum. 
Cremaster. 

Psoas,  sartorius,  iliacus,  pectineus,  adductors  of  the  thighs. 
Quadriceps  femoris,  gracilis,  obturator  externus  (?). 
Gluteus  medias  and  minimus,  tensor  fascite  latse,  semitendinosus, 

semimembranosus,  biceps  femoris. 
Pyriformis,  obturator  internus,  gemelli,  quadratus  femoris,  gluteus 

maxim  us,  long  extensors  of  the  foot  and  of  the  toes,  peroneus 

longus  and  brevis. 
Long  flexors  of  the  foot  and  of  the  toes,  large  calf-muscles,  small 

foot-muscles. 
Ejaculatory  and  verumontanum  muscles. 
Sphincter  and  detrusor  vesicae,  sphincter  ani. 
Levator  ani. 


The  exact  varieties  of  afferent  messages  which  the  posterior  roots 
conduct  into  the  cord  and  so  to  the  cortex  cerebri  and  elsewhere  in  the 
brain  have  not  been  defined.  Whatever  "sensations"  arrive  at  all, 
peripherally  started,  come  into  the  great  highway  and  coordinating  center 
through  these  roots  (save  for  those  which  come  by  way  of  the  afferent 
cranial  nerves).  Touch,  pain,  muscle  and  joint-sense,  heat-sense,  cold- 
sense,  and  that  ill-defined  sensibility  which  the  viscera  have,  are  among 
the  sorts  of  impressions  (some  conscious,  but  many  more  certainly  at 
least  .subconscious)  conveyed  inward  by  these  ventral  roots.  Much  as  in 
case  of  the  efferent  roots,  the  areas  .supplied  by  different  roots  overlap, 
e.specially  in  the  extremities,  .so  that  every  portion,  at  least  of  the  skin, 
is  supplied  with  sensation  by  at  least  two  roots.  In  some  cases  the  area 
supplied  by  the  roots  of  one  side  extend  somewhat  into  the  other  side  of 
the  body.  Head  and  Dana  have  .shown  how  certain  visceral  areas  are 
in  close  connection  with  certain  regions  of  the  surface  of  the  body — the 
.so-called  principle  of  referred  pain.  Thus,  for  example,  in  the  same 
direction,  hip-joint  disease  produces  pain  at  the  inside  of  the  knee,  and 


PLATE    IV 


€67 


Scheme  of  the  Various  Areas  of  Sensibihty  Represented  by 

Spinal  Segments  (the  front  of  the  body  on  the  left  of 

the  pi<iture,  the  back  on  the  right).     (Kocher. ) 

The  letters  C,  D,  L,  and  5  refer  to  the  cervical,  dorsal,  lumbar,  and  sacral  segments 
respectively,  as  indicated  further  by  the  numbers. 


CERTAIN  SETS  OF  NERVES 


93 


many  similar  relations  are  being  gradually  worked  out  clinically.  Landois 
gives  the  following  as  the  general  spinal  distribution  of  the  viscera:  The 
heart  and  lungs  are  represented  by  the  tenth  cranial  and  by  the  upper 
thoracic  nerves;  the  stomach,  small  intestine,  liver,  spleen,  and  pancreas 
by  the  vagus  and  the  middle  inferior  thoracic  and  upper  lumbar  nerves; 
the  adrenals,  kidneys,  testicles,  ovaries,  and  uterus  by  the  middle  and 
lower  thoracic  and  the  upper  lumbar  nerves;  the  rectum,  prostate,  penis, 
uterus,  and  vagina  by  the  sacral  nerves  and  the  hypogastric  plexus,  which 
last  in  turn  is  supplied  from  the  lower  dorsal  and  upper  lumbar  cord. 
In  certain  animals  some  motor  fibers  pass  out  through  the  dorsal  roots 
(Morat  and  Bonne)  and  in  some  mammals  the  vaso-clilators,  for  certain 
parts  at  least,  go  by  the  same  unsymmetrical  paths.  If  these  conditions 
obtain  in  man,  however,  their  details  have  not  as  yet  been  made  out. 


Fig.  47 


Diagram  of  the  neurone?  of  a  spinal  ganglion,  showing  their  relations:  p.r.,  posterior  root; 
a.r.,  anterior  root;  p.s.,  posterior  branch,  and  a.s.,  anterior  branch  of  a  spinal  nerve;  w.r.,  white 
ramus  communicans;  a,  large,  and  h,  small  spinal  ganglion  cells  with  bifurcations;  c,  one  of 
Dogiel's  types  of  ganglion  cells;  8,  multipolar  cell;  d,  nerve-fiber  from  a  sjTnpathetic  ganglion 
terminating  in  pericellular  plexuses.      (Dogiel  and  Bohm,  and  Davidoff  and  Huber.) 


In  Plate  IV  is  given  the  distribution  of  the  spinal  posterior  roots,  accord- 
ing to  Kocher  as  he  finds  it  indicated  by  human  pathological  inquiry,  the 
two  halves  of  the  picture  representing  respectively  the  front  and  the  back 
of  a  man.    A  similar  map  made  by  Head  mostly  corresponds. 

The  Sympathetic  Nerves. — The  quasi-system  of  neural  structures  known 
by  the  name  sympathetic,  consists  of  three  sets  of  ganglia  and  the  fibers 
connecting  and  serving  them.  The  first  set  of  ganglia  are  those  of  the 
gangliafed  cord,  about  twenty-two  in  number  on  each  side.  They  extend 
from  the  base  of  the  skull  to  the  coccyx,  and  are  classed  as  cervical, 
dorsal,  lumbar,  and  sacral.  The  second  set  are  the  ganglia  (solar,  hypo- 
gastric, pelvic,  etc.)  of  the  prevertebral  plexuses.  The  third  set  are  the 
much  smaller  peripheral  groups  of  cells  situated  in  the  various  viscera 
(e.  g.,  in  the  plexuses  of  Auerbach  and  the  no  less  essential  ganglia  of  the 


94 


THE  XERVOUS  SYSTEM 


Fig 


uterus  and  the  heart).  The  cells  of  these  various  nuclei  connect  directly 
by  contact  with  the  medullated,  white  neuraxones  of  cells  seated  prob- 
ably in  the  lateral  horn  of  the  spinal  cord  or  in  the  homologous  region 

of  the  brain  (Hiiber).  The 
cells  of  the  gangliated  cord 
(but  not  those  of  the  preverte- 
bral ganglia)  send  outward 
fibers  (known  as  those  of 
Remak)  which  are  "gray," 
i.  e.,  non-medullated.  These 
are  distributed  exclusively 
to  smooth  muscle-fibers  and 
perhaps  to  epithelium  all  over 
the  body  by  way  of  the  spinal 
nerve-trunks.  The  branches 
to  the  spinal  nerves  and  be- 
yond are  the  so-called  gray 
rami  communicantes,  while 
the  fibers  arising  in  the  gan- 
gliated cord  above  referred 
to  are  the  white  rami.  The 
latter  are  found  only  from  the 
dorsal  and  first  one  or  two 
lumbar  spinal  nerves,  but  the 
gray  rami  extend  to  each  of 
the  spinal  nerves,  each  gang- 
lion sending  inward  axones 
to  two  or  three  of  them.  The 
prevertebral  ganglia  send. non- 
medullated  fibers  to  the  vis- 
cera of  the  thorax  and  the 
abdomen,  continuing,  doubt- 
less more  or  less  altered,  the 
messages  they  receive  from 
the  gray  matter  of  the  cord 
or  from  the  small  much- 
branched  cells  of  the  gan- 
glia of  the  gangliated  cord. 
The  peripheral  ganglia  in 
similar  manner  retail  to  the 
tissues  in  which  they  are 
situated  the  motor  (and  se- 
cretory?) influence  they  re- 
ceive from  the  cord's  gray 
matter  direct,  from  the  ganglia  of  the  gangliated  cord,  or  from  the  pre- 
vertebral ganglia.  Dogiel's  recent  work  on  the  heart-action  well  illus- 
trates the  work  of  these  peripheral  ganglia. 


Diagram  of  the  sympathetic.      (Flower.) 


CERTAIN  SETS  OF  NERVES  95 

The  pre-ganglionic  fibers  are  those  which  connect  the  cord  and  the 
ganghon-cell,  while  the  post-ganghonic  fibers  are  peripheral  to  the  latter. 
It  appears  that  all  the  impulses  given  out  by  sympathetic  fibers  pass  over 
both  of  these  paths.  In  other  and  more  direct  terms,  it  is  not  apparent 
on  the  neurone  theory  that  impulses  originate  in  the  sympathetic  ganglia, 
the  presumption  being  rather  that  the  exciting  influence  always  comes 
more  or  less  directly  from  the  central  nervous  system  proper.  Perhaps, 
nevertheless,  influences  do  originate  in  these  ganglia  as  well  as  in  other 
knots  of  neuro-fibrils  or  masses  of  nerve-cell  tissue.  This  problem  is 
still  unsolved.  The  fact  that,  under  abnormal  conditions,  the  heart,  for 
example,  may  continue  its  beat  after  all  "nerves"  attached  to  it  have 
been  "cut,"  does  not  prove  that  normally  the  organ  does  not  receive 
continually  influences  from  the  complex  medulla,  through  these  periph- 
eral ganglion-cells.  On  the  other  hand,  the  same  phenomena  demon- 
strate that  either  the  heart-muscle  or  the  nerve-cells  within  it  have  auto- 
matic powers  dependent  on  their  own  metabolism,  at  least  for  a  time. 
Between  these  two  theoretic  drifts  the  exact  balance  has  not  yet  been 
made:  we  do  not  know,  in  fine,  how  much  or  how  little  in  the  way  of 
actual  energy-liberation  the  nervous  system  performs.  If  it  liberates  much 
exciting  energy  M^e  have  no  reason  to  deny  to  the  cells  of  the  sympathetic 
their  proportion  of  this  essential  work  (e.  cj.,  in  the  heart  or  the  uterus). 

The  sympathetic,  unaided  by  other  autonomic  nerves  (see  below) 
actuates  the  bloodvessels,  glands,  and  smooth  muscles  of  the  skin,  the 
bloodvessels  of  that  part  of  the  intestine  between  the  mouth  and  the 
rectum,  of  the  glands  opening  into  this  portion  of  the  gut,  and  possibly 
also  the  spleen  and  the  internal  generative  organs.  In  general  terms, 
then,  if  we  may  accept  this  estimate  tentatively  as  correct,  it  is  the  func- 
tion of  the  sympathetic  to  innervate  much  of  the  body's  smooth  muscle 
tissue  wherever  its  fabric,  extending  so  widely  through  the  body,  occurs. 

For  example,  the  pilomotors,  the  tiny  muscles  whose  contraction 
erects  the  hairs,  are  under  this  kind  of  influence.  This  suggests  one 
conspicuous  way  in  which  the  sympathetic  is  controlled — namely, 
from  the  midbrain,  at  least  in  emotional  conditions.  The  inhibitory 
effects  of  the  sympathetic  action  are  as  important,  if  not  as  widespread, 
as  those  of  the  actual  production  of  movement.  A  second  possible 
immediate  duty  of  these  nerves  is  still  somewhat  in  doubt  histologically — 
namely,  the  actuation  of  secretion  directly  by  innervation  of  the  secretory 
protoplasm.  If  this  connection  between  nerve  and  cell  interior  regularly 
occurs,  the  sympathetic  is  the  agent  of  the  control.  Where  it  does  not 
occur,  on  the  other  hand,  secretory  control  is  brought  about  through 
vasomotion.  As  the  sympathetic  surely  directs  this  process,  secretion 
in  any  case  is  under  the  management  of  this  "system." 

But  besides  these  two  efferent  fimctions  (whether  from  the  central 
nerve-system  or  only  from  the  sympathetic 's  vertebral  or  prevertebral  or 
peripheral  ganglia)  the  sympathetic  has  minor  afferentfunctions  of  various 
sorts.  These  impulses  pass  inward  apparently  on  both  the  gray  and 
the  white  rami,  although  onlv  the  latter,  according  to  Langlev,  has  been 


96 


THE  XERVOUS  SYSTEM 


actually  provetl  to  contain  them.  It  is  through  these  afferent  fibers  that 
the  viscera  possess  that  indefinite  sort  of  touch  sense  which  they  have, 
and  their  pain  sensations.  The  afferent  fibers  are  only  few  compared  with 
those  which  are  efferent:  Langley  and  Anderson  found  one-tenth  of  the 
meduUated  axones  in  the  hypogastric  nerves  to  be  afferent.  It  is  by 
these  latter  fibers  that  the  phenomena  of  referred  pain  are  brought 
about.  It  cannot  be  doubted  that  the  afferent  nerves  of  the  sympathetic 
are  more  widespread  than  at  present  we  actually  know  them  to  be. 

The  functions  of  the  sympathetic  and  of  the  other  autonomic  nerves 
are  tabulated  nearly  thus  by  Langley: 


Sympathetic. 

Other  Autonomous  Nerves. 

Midbrain's 

autonomous 

nerves. 

Contraction  of  the  iris  dilators. 

Contraction  of  the  smooth  orbi- 
tal muscles. 

Contraction   of   the  ocular  ar- 
teries. 

Contraction  of  the  iris. 
Contraction  of  the  ciliary  muscles. 

Bulbar  autono- 
mous nerves. 

Acceleration  of  the  heart  and 
contraction  of  the  bloodves- 
sels of  the  mucous  membranes 
of  the  head. 

Inhibitory  and  motor  action  on 
the    smooth   musculature    of 
the  gut  from  the  oesophagus 
to  the  descending  colon. 

?  Secretion  in  the  stomach,  liver 
and  pancreas. 

Contraction  of  the  bloodvessels 
from  the  oesophagus  to    the 
descending  colon. 

?  Contraction  of  the  bloodvessels 
of  the  lung. 

Contraction  of  the  bloodvessels 
of  the  intestines. 

Contraction  of  the  smooth  mus- 
culature of  the  spleen,  ureters, 
and  internal  sexual  organs. 

Contraction  of  the  smooth  mus- 
cles and  arteries,  and  secretion 
in  the  skin. 

Inhibition  of  the  heart  and  (dilata- 
tion) of  the  bloodvessels  in  the 
mucous  membranes  of  the  head. 

Motor  and  inhibitory  action  on  the 
smooth  musculature  of  the  gut 
from  the  oesophagus  to  the  de- 
scending colon. 

(?)  Secretion  in  the  stomach,  liver, 
and  pancreas. 

Sacral  autono- 
mous nerves. 

1 

Contraction  of  the  arteries  of 
the  rectum,  anus,  and  exter- 
nal sexual  organs. 

Iniiibition    and    contraction  of 
the  smooth  muscle  of  tiie  de- 
scending colon,   rectum,  and 
anus. 

Iniiibition    and    contraction   of 
tlie  bladder. 

Contractif)n  (and  ?  inhibition)  of 
the  urethra. 

Contraction  of   the  muscles  of 
the  external  sexual  organs.      1 

Inhibition  of  the  arteries  of  the 
rectum,  anus,  and  external  sex- 
ual organs. 

Contraction  of  the  smooth  muscu- 
lature of  the  descending  colon, 
rectum,  and  anus. 

Contraction  of  the  smooth  muscle 
of  the  anus. 

Contraction  of  the  urinary  bladder. 

Inhibition  (and  ?  contraction)  of 
the  urethra. 

Inhibition  of  the  muscles  of  the 
extern5\l  sexual  organs. 

THE  NERVOUS  IMPULSE  97 

Other  Autonomic  Nerves. — Langley  has  introduced  the  term  autonomic 
to  inchide  "the  contractile  cells,  unstriated  muscle,  cardiac  muscle,  and 
gland  cells  of  the  body,  together  with  the  nerve  cells  and  fibers  in  con- 
nection with  them.  The  autonomic  nervous  system  consists  of  the  sym- 
pathetic system,  which  we  have  already  in  part  considered,  of  the  cranial 
autonomic  system,  the  sacral  autonomic  system,  and  the  enteric  system." 
The  nerves  supplying  the  sorts  of  tissue  first-named  al)ove  not  supplied 
by  the  sympathetic  come  from  the  other  autonomic  nerves,  cranial, 
sacral,  and  enteric.  In  the  most  general  terms  the  cranial  autonomic 
nerves  (the  third,  seventh,  ninth,  tenth,  and  eleventh)  supply  certain 
parts  and  functions  at  the  upper  end  of  the  alimentary  canal.  The 
sacral  autonomic  system  (which  are  all  fibers  connected  with  the  pelvic 
nerve,  "nervus  erigens")  serves  various  parts  near  the  lower  end  of  the 
same  canal — rectal  muscles,  generative  muscles,  vasomotor  muscles,  etc. 
The  enteric  system  consists  of  the  plexuses  of  Auerbach  and  of  ^leissner. 
These  are  unique  neural  nets  extending  from  the  middle  of  the  esophagus 
to  the  anus.  Whether  these  two  systems  of  nerve-cells  and  fibers  are 
connected  with  the  cord  and  brain  by  sympathetic  or  by  cranial  and 
sacral  autonomic  fibers,  is  as  yet  not  known.  They  are  so  unlike  the 
other  nerves  of  the  sympathetic  that  they  may  be  properly  classed 
separately. 

This  division  of  what  used  to  be  known  as  the  "sympathetic  system" 
into  the  sympathetic,  cranial,  sacral,  and  enteric  systems  is  a  step  in  the 
important  direction  of  unravelling  the  set  of  nerve-fibers  whose  general 
functions  w^e  have  "just  suggested.  The  danger  is  rather  of  too  little 
analysis  and  classification  than  of  too  much,  for  scarcely  yet  is  the 
complexity  of  the  nerve-fibrils  necessary  to  the  actually  observed  com- 
plexity of  function  adequately  realized. 


THE  NERVOUS  IMPULSE. 

Despite  the  large  amount  of  work  put  upon  it,  the  real  nature  of 
the  nervous  impulse  is  today  as  uncertain  as  ever  it  was.  There  have 
been  many  speculations  as  to  the  means  by  which  the  nervous  influence  is 
transferred  along  the  nerve.  Some  of  these  now  appear  absurd  indeed 
to  us.  For  example,  it  was  at  one  time  supposed  that  the  nerve-fiber 
was  in  effect  a  string  which  was  in  some  way  pulled  on  by  the  brain, 
much  as  a  boy  pulls  a  jumping-jack.  Another  supposition  was  that  the 
nerve  was  a  tube  and  that  the  impulse  passed  literally  in  a  stream 
through  it.  Some  thought  that  the  movement  along  the  nerve  was  a 
mechanical  vibration,  as  others  still  think  that  it  may  be  a  vibration  of 
a  molecular  sort.  More  recent  suppositions  have  been  that  the  impulse 
is  of  an  electrical  nature,  such  as  rims  along  a  telegraph  wire.  A  still 
more  recent  supposition  is  that  it  is  a  progressive  coagulation  of  a 
colloidal  material  of  the  nerve  tissue  brought  about  by  ionic  influences. 
Finally,  we  may  note  that  it  is  commonly  thought  that  the  impulse  is  a 
7 


98  THE  NERVOUS  SYSTEM 

chemical  change  of  some  sort  passing  along  the  nerve.  As  is  well  recog- 
nized, there  is  a  tendency  in  Physics  today  to  unify  so-called  molecular, 
electrical,  and  chemical  changes.  It  becomes  more  certain  continually, 
therefore,  that  the  nervous  impulse  is  of  a  nature  somewhat  akin 
to  these.  That  it  is  any  one  of  them  alone,  we  cannot  at  present  say. 
Whatever  be  the  nature  of  the  impulse,  it  can  be  shown  that  it  passes 
progressively  from  one  portion  of  a  nerve  to  the  next  at  a  rate  not  very 
rapid,  and  that  it  produces  various  changes  on  its  way,  especially  of  an 
electrical  nature.  Whether  there  is  an  electrical  variation  during  the 
passage  along  a  nerve  which  is  absolutely  normal  in  an  unharmed 
animal,  we  are  not  certain.  It  is  probable  that  an  exceedingly  small 
amount  of  heat  also  is  produced  by  the  process  of  nervous  conduction, 
although  all  attempts  to  measure  it  have  so  far  proved  futile,  even 
with  very  delicate  electrical  thermometers. 

Whatever  its  nature,  the  nervous  impulse  conveys  exciting  energy 
rather  than  efficient  energy.  It  is  the  protoplasm  of  the  muscle  or  the 
epithelium  which  provides  the  energy  for  its  work — the  nervous  impulse 
only  activates  it  and  changes  it  from  potential  to  kinetic.  The  nerve- 
energy  is  many  millions  of  times  the  smaller  in  amount. 

The  speed  of  the  nervous  impulse  varies  in  diiTerent  conditions  and  in 
difi'erent  nerves.  Thus,  in  general,  heat  somewhat  accelerates  this  as  it 
does  most  other  functions,  and  we  find  the  rate  higher  in  the  so-called 
warm-blooded  animals  (homotherms)  than  in  cold-blooded  animals 
(poikilotherms).  A  frog's  sciatic  shows  a  rate  varying  between  10  and 
27  meters  per  second,  according  to  the  time  of  year,  etc.  In  the 
afferent  nerves  of  man  the  speed  is  45  or  even  50  meters  per  second. 
In  the  efferent  channels  the  rate  of  conduction  is  less,  and  ranges  fiom 
30  to  35  meters  per  second.  It  seems  to  vary  not  a  little  in  different 
nerves  even  of  the  same  general  sort.     (See  Appendix,  Experiment  79.) 

Nerves  conduct  their  currents  in  both  directions,  in  the  abnormal  as 
well  as  in  the  normal  direction.  This  is  readily  shown  in  the  common 
laboratory  experiments  with  the  sartorius  muscle  split  at  its  iliac  end. 
(See  Appendix,  Experiment  77.)  Whether  or  not  the  nerves  of  the 
uninjured  animal  ever  transmit  impulses  in  two  directions  is  not  known. 
The  ordinary  presumption  is  that  they  do  not,  because  of  the  arrange- 
ment of  their  terminal  connections,  if  for  no  other  reason. 

Chemical  agents  effect  the  conductivity  of  nerves  in  various  compli- 
cated ways.  (See  the  experiments  in  the  Appendix.)  For  example, 
carbon  dioxide  poured  about  an  isolated  frog's  sciatic  lessens  the 
excitability  of  the  nerve  but  does  not  change  its  conductivity.  On  the 
other  hand,  the  vapor  of  ethyl  alcohol  stops  the  transmission  of  the  ner- 
vous impulse  l)ut  does  not  lessen  tiie  irritability  of  the  nerve-protoplasm. 
From  work  by  Overton  and  by  Myer  it  appears  likely  that  this  action  of 
alcoholic-  va})or  is  the  type  of  the  action  of  all  anesthetics  on  the  nervous 
system. 

ElectrifMty  in  constant  current  acts  in  a  more  complicated  way, 
for  at  the  aiuxle  the  excitability  is  lessened   (anelcctrotonus),  while  at 


THE  XERVOUS  IMPULSE  99 

the    cathode   it    is    increased    (catelectrotoniis).      The    conductivity    is 
diminished. 

By  these  effects  of  electricity  and  of  the  agents  mentioned  before, 
it  is  clear  that  while  conduction  is  the  specialized  function  of  nerve, 
the  tissue  still  retains  the  irritability  common  to  all  protoplasm,  and 
the  two  may  vary  indej)endently  of  each  other.  The  conductivity 
of  the  nerve,  then,  whatever  its  specific  process,  is  something  different 
from  the  irritability  of  other  tissues.  The  nervous  impulse  is  readily 
actuated  not  only  by  electricity,  but  also  by  rapid  changes  of  tem- 
perature either  way,  by  mechanical  impact,  or  l)y  irritating  chemical 
substances.  However  set  in  movement,  the  nervous  impulse  is  accom- 
panied or  preceded  by  currents  which  are  truly  electrical,  as  may  be 
readily  shown  by  instruments  for  the  indication  and  measurement  only 
of  electricity.  It  has  never  been  proved  yet  that  nerves  originate  the 
impulses  which  pass  over  them.  The  energy  necessary  for  starting  the 
impulse  comes  probably  either  from  the  bodily  tissues  (mechanically, 
thermally,  chemically,  or  electrically  acting)  or  else  from  outside  the 
organism  altogether.  This  must  not  be  stated,  however,  too  abso- 
lutely, for  the  nerve-tissue  has  metabolism  as  well  as  the  other  tissues, 
and  an  amount  of  energy  proportional  to  the  mass  of  the  nervous  sys- 
tem may  be  generated  within  it.  Probably  this  energy  or  part  of  it 
goes  to  the  origination  of  nervous  impulses  as  well  as  to  supporting  them. 
Although  so  important,  this  question  has  as  yet  no  sort  of  certain 
answer. 


CHAPTEE    III. 


RESPIRATION. 


Of  all  the  functions  of  living  animals,  respiration  perhaps  is  the  most 
general.  The  union  of  oxygen  with  the  tissues  and  the  removal  of  the 
consequent  oxidation-products  is  at  the  basis  of  metabolism.  We  may 
define  respiration  then  as  essentially  an  interchange  of  oxygen  and  of 
carbon  dioxide  between  the  tissue-protoplasm  and  the  atmosphere. 
So  long  as  these  requirements  are  fulfilled,  whatever  the  means,  how- 
ever superficial  or  deep  the  tissues  lie,  respiration  is  going  on.  In  man  it 
is  obvious  that  almost  all  of  his  tissue-cells  are  so  far  away  from  the 
atmosphere  that  there  can  be  no  direct  interchange  between  them  and  the 
oxvffen  and  carljon  dioxide  in  the  air.    Even  the  skin  in  the  case  of 


Fig.  49 


Head  and  gills  ot  the  mud-puppy  (Necturus),  to  show  direct  respiration  in  a  relatively 
highly  developed  animal.      (Dalton.) 

man  performs  no  respiration  directly  with  the  atmosphere,  for  its  outer 
layers  are  essentially  dead,  while  its  inner  layers  are  supplied  much  as 
are  the  inmost  tissues  of  the  body.  Francke  estimates  that  an  average 
human  body  is  made  up  of  400,000,000,000,000  cells,  Avhile  another  esti- 
mate makes  the  number  26,500,000,000,000.  Every  one  of  these  requires 
oxygen,  and  exhales  car}>on  dioxide.  The  biological  problem  then  in  the 
case  of  man  is  how  to  supply  an  a])undance  of  oxygen  to  all  these  cells  and 
how  to  remove  the  products  of  their  combustion.  Thus,  in  practice  the 
conspicuous  part  of  respiration  is  the  mechanical  means  of  taking  in 
and  giving  out  respiratory  gases.  The  essential  process,  however,  is 
the  interchange  of  these  gases  between  the  living  protoplasm  and  the 
atmosphere.  The  pulmonary  part  of  the  process  is  called  external 
respiration,  while  the  essential  intercellular  interchange  is  called  internal 
respiration. 

The  Chemistry  of  Respiration  Proper. — Before  taking  up  a  systematic 
description  of  the  respiratory  j)nKc.s.s  as  a  unified  system  of  events,  the 


RESPIRATION  101 

chemical  relations  of  the  tissues  to  the  atmosphere  must  be  briefly  dis- 
cussed, and  in  a  most  general  way  the  biochemistry  of  oxidation. 

Oxidation  is  a  process  probably  more  nearly  universal  on  the  planet 
Earth  than  any  other  chemical  reaction  with  which  we  are  familiar. 
One-half  of  the  crust  of  the  world  is  oxygen,  as  is  more  than  one-fifth  of 
the  atmosphere  and  about  four-fifths  of  all  the  water.  Oxygen  is  the 
source  of  all  "combustion,"  and  furnishes  to  organisms  one  of  their 
sources  of  energy.  Not  only  all  animals  but  also  all  plants  (a  few  indi- 
rectly) are  dependent  on  oxygen  for  their  living.  Oxygen  combines 
with  all  "elements"  so  far  isolated  (except  fluorine).  This  fact  partly 
accounts  for  its  very  wide  distribution  in  nature.  The  protein  particle 
contains  oxygen,  and  so  does  the  carbohydrate  molecule,  the  molecule 
of  fat,  and  that  of  albuminoid.  Moreover,  each  of  these  molecules 
contains  carbon,  with  a  strong  affinity  for  oxygen,  and  this,  when  satis- 
fied, gives  rise  to  carbon  dioxide.  Later  on,  in  the  chapter  on  Nutrition, 
we  shall  study  somewhat  more  in  detail  the  metabolic  processes  of  the 
body.  The  important  fact  now  is  that  the  atmosphere  and  the  food  con- 
tain both  oxygen  and  carbon,  and  that  these  are  prominent  also  in  the 
animal  tissues.  Life  in  its  basis  is  but  a  physiological  succession  of 
anabolism  (building-up),  and  of  katabolism  (tearing-down),  the  vital 
animal  energies  being  made  kinetic,  apparent,  useful,  in  the  latter  or 
katabolic  process.  Even  tissues  excised  from  the  body  of  an  animal 
respire,  that  is,  absorb  oxygen  and  give  off  carbon  dioxide.  Thus,  Bert 
obtained  from  the  tissues  of  a  dog  recently  killed  an  interchange  of 
the  two  gases  in  twenty-four  hours  as  follows: 

Respiratiox  of  Excised  Tissues. 
Cubic  centimeters  of  gas  per  100  grams  of  tissue. 

Tissue.  Oxyge.  absorbed.     C-bondteide 

Muscle 50.8  56.8 

Brain 45.8  42.8 

Kidney 37.0  15.6 

Spleen 27.3  15.4 

Testis 18.3  27.5 

Broken  bone  and  marrow  ....  17.2  8.1 

These  quantities  are  interesting  because  they  prove,  among  other 
things, that  respiration  is  inherent  in  living  tissues.  A  molecule  of  proto- 
plasm in  the  dying  muscle  from  a  dog  respires  quite  as  does  a  molecule 
of  the  protoplasm  of  an  ameba  or  of  a  human  spermatozoon.  Nothing 
further  is  needed  to  prove  that  the  animal  combustion  which  requires 
the  oxygen  and  produces  the  carbon-dioxide  takes  place  in  the  tissues 
themselves,  and  not  for  the  most  part  in  the  circulating  blood,  as  was 
formerly  supposed.  The  blood  is  a  tis.sue  and  has  its  share  of  direct 
oxidation,  but  most  of  the  oxygen  absorbed  into  the  body  goes  as  directly 
into  the  protoplasmic  cells  of  the  tissues  as  the  complexity  of  the  struc- 
tural conditions  will  allow. 


102 


RESPIRATION 


The  oxytjen  absorbal  furnishes  one  of  the  elements  of  the  combustive 
katabohsm  by  which  hfe  is  manifested.  Partial  katal)olism  is  apparently 
always  primary  and  oxidation  secondary — namely,  in  the  combustion 
of  the  first  products  of  the  katabolism.  About  the  details  of  this  union 
of  the  oxygen  and  the  tissue-molecules  we  know  but  very  little.  We  are 
sure  what  some  of  the  end-products  of  these  complicated  chemical 
reactions  are,  as  will  be  seen  later  in  the  chapter  on  Nutrition;  and 
we  know  that  carbon  dioxide  is  the  chief  of  these  end-products,  the  most 
universal  in  the  tissues.  It  is  the  one  representative  of  the  actual  com- 
bustion of  the  cells,  especially  of  the  fats  and  carbohydrates  of  the  tissues 
and  of  the  still  circulatino^  food  as  well.     When  wood  or  coal  is  burned 

in    the    air,  oxygen   is   used   up 
Fig.  50  and  carbon  dioxide,  the  union- 

product  of  the  carbon  and  the 
oxygen,  is  given  off.  Moreover, 
heat  is  liberated,  and,  with  the 
proper  mechanisms  attached, 
energy  of  several  forms.  In 
these  respects,  at  least,  bio-meta- 

FiG.  51 


Section  through  the  gills  of  the  lamprey  (Am- 
mocaetes):  ks,  gill-cavity;  kb,  anterior,  and  kb^, 
posterior  gill-plates;  z,  septum;  ka,  gill-artery; 
uv,  vein;  vm,  ventral  body-muscle;  e,  epithe- 
lium.     fB.   Haller.) 


Section  through  the   nasal   cavities  of  the 
duck-bill  fOrnitliorhynchus).    (Zuckerkandl.) 


Fig.  52 


Z' 


|p|o|o  I  o|_o|o|ojo|o|o|o|ojo)o|ojo|o;o 


b>nep 


Diagrammatic  section  of   the  gill-plate   of  a  fish:     ep,  epithelium;   bl,  erythrocytes;   z,  cells 
of  the  bloodvessels;    bm,  basal  membrane;   2',  bloodvessel.      (Marianne  Plelin.) 

holism  is  like  the  oxidation  in  a  steam-engine's  furnace.  Because  of 
these  similarities  it  has  long  been  customary  to  speak  of  the  combustion 
going  on  in   the  body,  of  the  "life-giving  oxygen,"  of  the  food  as  the 


RESPIRATION 


103 


fuel  of  the  organism,  of  the  kings  as  the  chimney,  etc.  Such  similes 
are  instructive  and  fairly  well  represent  the  facts  so  far  as  they  go. 

A  living  organism,  however,  is  very  different  in  its  working  conditions 
from  a  steam-engine  plant.  It  is  more  automatic,  less  dependent  on 
external  conditions,  has  principles  and  tendencies  of  its  own,  and  habits 
structural  and  functional,  in  a  much  greater  degree  than  has  the  steam- 
engine  and  its  boilers.  One  unlikeness  is  fundamental  and  must  be 
specifically  noted  here.  Whereas  in  the  boiler-furnaces  the  draft,  that  is 
the  relative  abundance  of  oxygen,  determines  directly  the  speed  and 
vigor  of  the  combustion,  in  organisms  the  combustion  or  metahoUsm  is 
largely  the  controlling  agent,  and  not  the  oxygen.  It  is  not  possible  by 
a  "forced  draft"  to  hasten  beyond  its  normal  maximum  the  combustive 
metabolism  in  living  tissues.  They  absorb  no  more  oxygen  when  the 
animal  breathes  only  this  gas  than  they  do  from  the  ordinary,  average- 
pure  atmosphere  to  which  the  tissues  are  adapted  by  evolution.  Indeed, 
when  the  arterial  blood  has  been  forced  to  absorb  one-third  more  than 
its  normal  quantity  of  oxygen  by  subjecting  the  animal  to  an  oxygen- 
pressure  of  six  atmospheres  the  animal  dies,  from  a  lowering  of  the 
vital  metabolism  of  some  or  other  of  the  tissues  (Paul  Bert).  The 
metabolism  thendeterminesthe  amount 
of  oxygen  needed  by  the  tissues,  rather 
than  that  the  supply  of  the  gas  nor- 
mally affects  the  tissue-metabolism. 

Various  conditions  help  to  determine 
the  amount  of  oxygen  consumed  by  the 
tissues  as  also  the  amount  of  carbon 
dioxide  excreted.  Anything  in  general 
which  increases  the  metabolism  either 
in  intensity  or  in  extent  enlarges  the 
respiratory  exchange.  Voit  and  Pet- 
tenkofer  showed  that  in  a  man  of 
average  weight,  say  70  kg.,  about  700 
gm.  of  oxygen  are  required  in  twenty- 
four  hours,  while  about  800  gm.  of 
carbon  dioxide  are  given  off.  But 
during  rest  the  700  gm.  required  in 
average  activity  may  decline  to  600 
gm.  and  the  800  gm.  of  carbon  diox- 
ide excreted  may  decrease  even  more 

than  100  gm.  On  the  other  hand,  during  hard  muscular  work  the'con- 
sumption  of  oxygen  may  arise  to  1100  gm.  daily  and  the  amount  of 
carbon  dioxide  to  nearly  1300  gm.  As  an  average  for  the  adult's  demand 
for  oxygen,  Zuntz  states  about  14.5  gm.  per  kilo  of  body  weight  in 
twenty-four  hours. 

The  Respiratory  Mechanism. — There  is  no  space  here  for  a  description 
of  the  gross  and  microscopic  anatomy  of  the  respiratory  mechanism. 
This  must,  however,  be  thoroughly  kept  in  mind  in  all  its  details  if  the 


Two   infundibula   of    human   lung:     a 
and  b,  air-sac?;   c  c,  two  ultimate  bronchi. 

(Kolliker.) 


104 


RESPIRATION 


breathing  function  is  to  be  really  understood.     The  reader  must  have 
in  mind  the  structure  of  this  functional  system,  from  the  outer  edge 


Fig.  54 


Section  of  trachea:  a,  ciliated  epithelium  of  inner  wall;  b,  basement  membrane;  c,  elastic 
connective-tissue  layer;  d,  muscular  layer;  e,  gland;  f,  gland-duct;  g,  cartilage  lying  in  the 
fibrous  coat.      (Bates.) 

of  the  nostrils  to  the  diaphragm — the  nasal  fossae,  larynx,  trachea, 
bronchi,  lungs,  pleural  cavities,  thorax,  diaphragm,  and  the  nerves 
which  are  concerned  in  the  movements  of  all  of  these.     We  can  here 


Fig.  55 


Diaeram  of  a  lung  Uibule:  a,  is  placed  in  a  bronchial  tube;  b,  branch  of  pulmonary  artery; 
from  this  a  branch  passes  to  be  distributed  to  the  alveoli  of  the  lobule  as  seen  at  d;  e,  vein 
which  passes  on  the  outside  of  the  lobule  to  come  into  relation  witli  the  arterial  capillaries  in 
the  lobule;  e,  lobar  bronchiole;  /,  infundibulum  in  which  are  seen  the  alveoli.  (Bates,  modified 
from  Stoehr.) 

mention  a  few  only  of  the  conditions  which  are  the  most  essential  for 
our  purpose.     The  nose,  in   man,  is  very  largely  a  respiratory  organ. 


RESPIRATIOX 


105 


Fig.  56 


Its  vibrissse  (the  hairs)  strain  out  large  foreign  particles  in  the  draughts 
of  air.  The  organ  of  smell  not  only  warns  us  of  some  sorts  of 
unwholesome  air,  but  makes  us  breathe  more  deeply  when  the  air  is 
sweet  and  fresh.  The  nasal  fossse  are  larger  and  more  complex  than  is 
commonly  supposed,  and  are  lined  with  very  thick  vascular  mucosa, 
which  warms  to  the  body  temperature  and  saturates  with  moisture  the 
incoming  air.  Both  of  these  modifications  are  necessary  to  prevent 
injurv  to  the  sensitive  bronchi  and  the  lungs.  The  larynx  is  the  organ 
of  the  voice,  and  is  discussed  later  on.  It  is  rather  a  hindrance  to 
respiration  in  the  long  run  than  a  respiratory  organ,  although  the 
closing-down  of  the  epiglottis  over  the  trachea  and  bronchi  at  each  act 
of  swallowing  protects  the  latter  from  frequent  danger.  The  trachea 
is  ample  in  diameter,  and  kept  so  by  strong  cartilaginous  rings.  The 
ramifying  bronchi  finally  becomes  muscular  to  a  certain  extent,  and  so 
somewhat  control  the  air-supply  to  the  lungs. 

The  Lungs. — These  are  the  proper  organs  of  respiration,  and  must 
be  fully  understood  in  their  structure  and  mode  of  action.  The  two 
lungs  are  separated  by  the  mediastinum.  The  right  lung  weighs  about 
62.5  gm.  and  the  left  not  far  from  565  gm.  The  specific  gravity  of  the 
lung-tissue,  according  to  Gray,  is  from  345  to  746,  water  being  1000. 
To  the  touch,  it  is  a  highly  elastic, 
spongy,  and  crepitating  mass;  and  in 
appearance  it  ranges  from  a  light  pink 
at  birth  to  almost  black  in  old  age, 
darkening  largely  from  the  coal-  and 
other  dust  slowly  collecting  in  it. 

According  to  Rainey,  the  small  bron- 
chi after  entering  a  obule  of  the  lung 
subdivide  from  four  to  nine  times  con- 
formably to  the  size  of  the  lobule,  the 
smallest  branches  being  about  two- 
thirds  of  a  millimeter  (0.63  mm.)  in 
diameter,  or  smaller.  These  smallest 
subdivisions  of  the  air-tubes  then  lose 
their  cylindrical  shape  and  structure 
and  continue  onward  a  short  way  as 
infundihiila.  These  are  irregular  tubes 
from  which  the  short  alveoli  dilate  in 
various  places  and  directions.  Indeed, 
bronchioles  of  2  mm.  diameter  often 
have  alveoli  extending  outward  from 
them,  as  shallow  and  rounded  vesicles. 
Those  are  the  ultimate  chambers  for 
air  in  the  lungs,  and  it  is  from  them  and 
through  their  walls  that  the  two  respir- 
atory gases  osmose  and  diffuse  in  their  respective  directions,  inward  and 
outward. 


Scheme  of  the  lung  of  a  frog  to  show 
its  relatively  simple  lobulation:  G,  glottis; 
Z,  lobules;  .-1.  alveoli;  c,  lung-epithelium; 
a.  afferent  artery;  v,  vein;  a.p.p.,  serous 
covering.      (Renaut.) 


106 


RESPIRATION 


The  alveoli  or  air-cells  varv  in  diameter  from  i  to  |-  mm.  They  are 
composed  of  epithelium,  strengthened  with  a  thick  network  of  elastic 
connective  tissue.  The  epithelium  is  of  two  sorts,  a  large,  flat,  thin-celled 
variety  like  endothelium,  and  a  kind  composed  of  small  flat  polygonal 
nucleated  cells.  The  latter  lie  singly  or  in  small  groups  scattered  among  the 
cells  of  the  former  variety,  and  are,  it  is  supposed,  substitutes  ready,  after 
differentiation,  to  take  the  places  of  destroyed  cells  of  the  other  variety. 
Otherwise  their  special  purpose  is  quite  unknown.  It  is  possible  that  they 
may  have  some  specific  osmotic  powers,  as  probably  have  the  different 
sorts  of  epithelium  of  the  uriniferous  (kidney)  tubules.  (See  page  246). 
The  number  of  the  respiratory  alveoli  in  adult  human  beings  has  been 

Fig.  57 


Magnification  of  the  lung-area  by  the  alveoli.  Were  the  lungs  plain  sacs  instead  of  organs 
made  up  of  725,000,000  alveoli,  their  respiratory  capacity  would  be  only  about  one  two-thousandth 
of  what  it  is.      This  ratio  is  that  of  the  small  square  to  the  large. 


estimated  at  725,000,000.  Bearing  in  niiiid  the  vastncss  of  this  multitude, 
it  is  easier  to  believe,  what  appears  to  be  true,  that  the  combined  concave 
area  of  the  alveoli  is  about  200  scjuare  meters,  or  more  than  one  hundred 
times  the  entire  superficial  area  of  the  body.  This  is  the  size  of  the  air- 
layer  exposal  on  what  is  functionally  the  periphery  of  the  lungs.  Its  great 
size  makes  it  possible  to  understand  how  the  gaseous  interchange  can 
take  place,  for,  as  we  shall  see,  the  forces  which  bring  about  the  osmosis 
back  and  forth  through  the  alveolar  wall  are  .slight  and  can  have,  there- 
fore, small   intensive   action.     This   lack   of   intensity  is   made   up  by 


RESPIRATION 


107 


abundant  extensity,  as  has  just  been  seen  and  as  is  shown  graphically 
in  the  diagram.  A  layer  of  air  200  square  meters  in  size  separated 
from  a  like  extent  of  rapidly  moving  blood  by  only  two  layers  of  highly 


Fig.  58 


*•- 


Diagram  to  sbow  the  relations  of  the  air-chambers  to  the  lungs  in  a  carinate  bird  (e.  g.,  any 
American  bird).  The  lungs  are  the  shaded  portion  of  the  picture:  1,  cla\acular  air-sacs;  2, 
cervical  sacs;  3,  anterior,  and  4,  posterior  diaphragmatic  sacs;  5,  abdominal  sac;  h,  air  sac  in  tlie 
humerus.      (B.  Haller.) 

Fig.  59 


Two  alveoli  from  the  lung  of  a  goase.      The  right-hand  picture  shows  the  air-spaces  injected 
(black),  while  the  left-hand  view  is  that  of  the  injected  arterioles.      (F.  E.  Schulze.) 


108  RESPIRATION 

permeable  epithelium  each  yTnrir  i^^"^-  thick,  with  a  thin  layer  of  lymph 
between  them,  might  well  serve  as  an  organ  with  great  capabilities!  So 
closely  are  the  alveoli  packed  together  in  the  lung  that  besides  them  in 
these  large  organs  there  is  little  else  except  the  capillaries. 

The  Capillaries. — From  Fig.  57,  representing  the  histology  of  the 
luncr,  the  relation  of  the  capillaries  to  the  alveoli  is  obvious.  The  wall 
of  these  tubelets  (the  ultimate  bloodvessels,  and  those  which  alone 
immediately  supply  the  tissues)  is  simply  one  layer  of  flat  epithelial  cells, 
here  called  endothelium,  cemented  edge  to  edge  so  as  to  constitute  a 
tube.  Sihler  claims  that  a  plexus  of  fine  nerve-fibrils  surrounds  the 
capillaries  in  all  parts  of  the  body.  This  layer  of  protoplasm  is  often 
less  than  one  micron  in  thickness,  and  it  practically  lies  in  apposition  to 
the  alveolar  wall.  So  crowded  are  these  capillaries,  however,  all  over 
the  peripherv  of  the  alveoli  that  it  is  functionally  almost  a  continuous 

Fig.  60 


The  pulmonary  epithelium  of  a  young  dove:  a,  capillary;  h,  cell-groups  in  the  capillary 
flexus;  c,  contours  of  the  larger  epithelial  cells;  d,  a  capillary  mesh-opening  with  two  cell-islands; 
/,  capillary  opening  without  any  cell-groups.      (Elenz.) 

surface.  This  endothelial  layer,  together  with  the  alveolar  surface 
(in  contact  with  each  other  save  for  the  universal  moistening  lymph), 
constitutes  the  osmotic  animal  membrane  through  which  the  processes  of 
external  respiration  take  place.  This  is  the  living  protoplasmic  layer  to 
which  the  respiratory  tubes  conduct  air  and  from  which  they  lead  it  away 
into  the  atmosphere.  We  will  next  inquire  as  to  the  motor  power  of  this 
ceaseless  ebb  and  flow  of  waste  and  life-giving  gases. 

The  Thorax. — This  is  a  muscular,  IxMiy,  and  cartilaginous  box 
adapted  as  a  motor  organ  of  respiration.  The  sides  and  bottom 
of  this  flattened  and  conical  bellows  are  all  more  or  less  movable  by 
means  of  muscles,  of  which  the  diaphragm  is,  functionally,  the  most 
important.  '^J'he  ril)S  are  so  shayK'd  that  when  they  are  raised,  largely 
by  the  external  intercostal  muscles,  the  capacity  of  the  chest  is  increased 
laterally,  antero-posteriorly,  and  to  a  slight  extent  upward.    The  fibers  of 


RESPIRATION 


109 


the  external  intercostal  muscles  are  arranged  obliquely  between  the  ribs  in 
such  a  way  that  when  the  fil)ers  shorten  the  ribs  are  drawn  closer  together. 
Thus,  all  except  the  top  ribs  are  raise<l,  as  the  accompanying  diagram 


Fig.  61 


Anterior  view  of  the  thorax. 
Fig.  62 


Diaphragm  as  seen  from  below:  1,  2,  3,  the  three  lobes  of  the  central  tendon  connecting  the 
muscular  fasciculi  extending  from  the  lower  edge  of  the  thorax,  the  crura  (4,  5),  and  the  arcuate 
ligaments  (6,  7);  8,  aorta;  9,  esophagu.?;  10,  quadrate  foramen;  11,  psoas  muscle;  12,  quad- 
ratus  lumborum  muscle.      The  convexity  is  upward. 

makes  plain.  The  muscles  which  aid  these  intercostals  are  the  levatores 
costarum,  the  scaleni,  and  the  serrati  postici.  The  quadratus  lumborum 
connects  the  pelvis  with  the  last  rib,  and  by  its  tonic  resistance  holds  the 


110 


RESPIRATION 


latter  down  when  other  muscles,  especially  the  diaphragm,  tend  to  raise  it 
during  inspiration.    The  diaphragm  is  by  far  the  most  important  of  the 


Fig.  63 


Diagram  to  show  the  actions  of  the  intercostal  muscles:  S  C,  spinal  column;  D  E,  sterniun; 
A  D,  one  rib;  B  E,  the  next  rib;  /  M,  an  external  intercostal  muscle-fiber  in  its  rela.xed  state; 
/'  M' ,  the  same  in  its  contracted  condition.  Its  shortening  helps  to  raise  the  ribs  and  advance 
the  sternum  into  the  position  A  D'  E'  B.  The  internal  intercostals  act  on  the  same  principle, 
their  contraction  lowering  the  ribs. 

Fig.  64  ^ 


The  interco.stal  muscles,  etc.:  A,  lateral  view;  B,  rear  view;  1,  the  levatores  co.starum,  short 
and  long;  2,  the  external  intercostals;  3,  the  internal  intercostals  seen  on  removal  of  the  external 
set.      The  internal  layer  if  seen  to  be  deficient  toward  the  spine.      (Cloquet.) 

muscles  of  respiration.    When  it  contracts,  its  dome-shape  central  portion 
flattens  out  somewhat.    This  increases  the  contents  of  the  thorax.    The 


RESPIRATIO\ 


111 


amount  of  this  depression  varies  between  1  cm.  in  ordinary  respiration 
to  2  or  3  cm.  in  deep  inspiration. 

The  expiratory  muscles  are  far  less  important  than  the  inspiratory 
because  the  process  of  expiration  is  largely  a  passive  recoil  of  tissues 
twisted  or  stretched  in  inspiration.  The  lungs  also,  as  we  have  seen, 
are  highly  elastic  and  tend  ever  to  contract  to  a  size  much  smaller  than 
that  when  thev  are  full.     The  muscles  of  the  abdominal  wall  also  aid 


Apparatus  to  show  the  pneumatic  relations  of  the  respiration  and  of  the  circulation:  A,  rep- 
resents the  thorax;  B,  the  diaphragm;  C,  the  glottis;  Z)  is  a  tube  leading  to  the  manometer, 
/,  indicating  the  intrathoracic  pressure  (while  E  runs  to  another  manometer  (not  shown)  indicating 
the  intrapulmonary  pressure);  (?  is  a  reservoir  (veins),  and  H  a  receiver,  connected  in  part  by 
the  thin  loose  tube  F;  at  T'  and  V'  are  valves;  K  represents  the  muscles  which  lower  the  dia- 
phragm in  inspiration.  When  this  occurs  the  heart  is  distended  and  the  suction  helps  to  draw  the 
blood  from  G  toward  the  heart  F,  the  valve  V'  preventing  suction  also  on  H.  The  same  suction 
draws  apart  the  suspended  rubber  bags  (lungs),  and  to  fill  this  increased  space  air  falls  in  through 
the  opening  C  (glottis).  When  the  diajjliragm  ascends  in  expiration  the  reverse  processes  occur. 
(Hering.)      (See  Experiment  30  in  the  .\ppendix.) 


expiration  by  contracting  to  a  slight  extent,  pressing  the  abdominal  con- 
tents against  the  diaphragm. 

The  internal  intercostal  muscles,  put  on  stretch  by  inspiration,  tend  to 
contract  in  expiration,  although  in  ordinary  breathing  they  are  used 
apparently  mostly  to  complete  the  thoracic  w^all  between  the  ribs.  In 
dyspnea   (difficult   breathing),   the  .abdominal   muscles,   especially  the 


112  RESPIRATION 

recti,  contract  and  press  the  abdominal  contents  upward  against  the 
diaphragm.  The  pectoral  muscles  also  aid  in  forced  respiration,  as  do, 
indeed,  at  times,  in  one  way  or  another,  nearly  all  the  muscles  attached 
to  the  thorax. 

The  Nerves. — The  nerves  employed  in  respiration  are  a  very  impor- 
tant part  of  the  mechanism.  It  is  necessary  that  the  parts  of  the 
apparatus  should  work  perfectly  together,  and  essential  that  the  respira- 
tory function  should  be  adapted  to  the  many  changing  conditions  of  the 

Fig.  66 

Internal. 


Externaf, 


True  respiration.      Internal   respiration  is  (?ie  interchange  between  the  tissue-cells  and  the  blood. 
External  respiration  is  the  interchange  between  the  blood  and  the  lung-alveoli. 

rest  of  the  organism.  The  afferent  nerves  of  respiration  pass  from 
different  parts  of  the  respiratory  tract  to  the  V:)reath-center  in  the  medulla 
oblongata.  Among  these  arc  the  fifth  cranial  (the  trigeminal),  the  first 
(olfactory),  the  laryngeal,  glosso-pharyngeal,  and  the  vagus.  Everyone 
is  aware  how  easily  a  sneeze  may  be  produced  by  a  sharp  stimulation  of 
the  nostrils,  and  inhibitefl  by  pressure  on  the  upper  lip.  The  afferent 
branches  of  the  vagal  nerves  probably  ramify  in  the  walls  of  the  lungs  of 


RESPIRATION  113 

the  alveoli  ami  so  continually  keep  the  movements  of  the  lungs  delicately 
in  touch  with  the  means  of  their  ventilation. 

The  respiratory  center  is  a  portion  of  the  gray  matter  of  the  brain 
which  controls  the  actions  of  the  respiratory  mechanism.  It  was 
discovered  by  Flourens.  He  observed  that  puncture  or  destruction  in  a 
certain  small  spot  in  the  medulla  oblongata  was  followed  immediately  by 
cessation  of  respiration,  which  coidd  not  be  recovered  from.  This 
switch-board  for  incoming  and  outgoing  respiratory  nervous  impulses  is 
now  known  to  be  bilateral,  below  the  vaso-motor  center,  and  near  the 
point  of  the  calamus  scriptorius  in  the  floor  of  the  fourth  ventricle  in 
the  medulla.  It  appears  also  that  one  part  of  this  minute  knot  of 
neurones  is  concerned  in  inspiration,  and  another  part  with  expiration. 
It  is  in  close  connection  with  the  center  of  the  vagus.  Some  authorities 
doubt  the  precisely  definite  location  w'hich  used  to  be  described,  and 
say  that  we  cannot  locate  it  more  closely  than  in  the  lower  portion  of 
the  medulla. 

This  center  is  unique  in  the  body  so  far  as  known,  in  that  it  is  controlled 
by  certain  definite  substances  present  in  the  blood-stream  which  flows 
through  it  and  around  its  nerve-cells.  This  fact  makes  it  in  technical 
terms  an  "automatic  center."  There  has  been  much  discussion  as  to 
whether  it  is  the  lack  of  oxygen  or  the  excess  of  carbon  dioxide  in  the 
blood  which  stimulates  it.  The  fact  seems  to  be  that  it  may  be  both 
of  these;  but  the  excess  of  carbon  dioxide  stimulates  it  much  more 
actively  it  is  probable  than  does  a  deficiency  of  oxygen.  Pfliiger  has 
suggested  that  some  easily  oxidized  substance  may  be  the  actual 
stimulant,  this  being  usually  absent  from  w^ell-oxygenated  blood.  Recent 
w^ork  by  Plavec  and  by  Laulanie  makes  it  still  more  probable  that  the 
immediate  stimulant  is  carbon  dioxide.  The  center  has  an  intimate 
association  with  about  all  the  other  important  nuclei  in  the  medulla. 
One  sees  this  readily  in  the  great  sensitivity  of  respiration  to  almost  all 
conditions,  emotional,  morbid,  etc. 

The  efferent  nerves  of  respiration  are  chiefly  the  phrenics,  certain  of 
the  intercostals,  and  the  vagus.  Of  these,  the  phrenics  are  perhaps  most 
essential  because  they  actuate  the  diaphragm,  which  is  the  essential 
respiratory  motor  organ. 

The  Process  and  the  Mechanism  of  Internal  Respiration. — The  means 
by  which  internal  respiration  is  carried  on,  the  essential  portion  of  the 
whole  process,  is  in  part  physical  without  being  mechanical,  and  in  part 
the  mechanism  of  another  functional  system — namely,  the  circulation. 
Internal  respiration  is  the  interchange  of  the  two  respiratory  gases 
between  the  blootl  and  the  tissue-protoplasm.  The  mechanism  of  the 
blood's  movement  is  one  part  of  this  process  and  the  passage  through 
the  animal  membranes  intervening  between  the  interior  of  a  capillary 
and  the  interior  of  a  tissue-cell  is  the  other  part.  The  circulatory 
mechanism  will  be  described  in  a  chapter  by  itself:  (See  page  278.) 
First,  then,  we  must  here  inquire  by  exactly  what  carrying  agents  the 
oxygen  and  the  carbon  dioxide  are  conveyed  between  the  alveoli  and  the 
8 


114  RESPIRATION 

tissues,  and  then  as  to  the  physical  principles  and  the  physiological  con- 
ditions which  are  concerned  in  the  passing  inward  of  the  oxygen  to  the 
cells  of  the  tissues  and  the  passage  of  the  carbon  dioxide  from  the 
tissues  to  the  deporting  blood. 

Of  the  (jQ  volumes  of  gas  which,  by  means  of  the  mercurial  air  pump, 
may  be  removed  from  100  volumes  of  the  blood  of  the  dog,  the  average 
composition  is  as  follows  (Halliburton) : 

Arterial  blood.        Venous  blood. 

Oxygen 20  8  to  12 

Carbon  dioxide 40  46 

Nitrogen 1  to  2  1  to  2 

The  oxygen  while  being  carried  in  the  distributing  blood  is  nearly  all  in 
loose  chemical  combination  with  the  hemoglobin  of  the  erythrocytes  or  red 
blood  corpuscles.  The  average  amount  of  oxygen  present  in  arterial 
blood  is  about  22  per  cent,  by  volume,  while  Pfliiger  found  that  plasma 
or  serum  (the  corpuscles  being  absent)  would  absorb  no  more  than  9.26 
per  cent,  by  volume.  Crystals  of  hemoglobin  have  the  power  of  absorbing 
large  amounts  of  this  gas.  Hiifner  found  in  100  gm.  of  ox-blood  crystals, 
as  a  mean  of  ten  analyses,  134  c.c.  Hemoglobin  (see  page  256  for  its 
phvsical  and  chemical  description)  will  from  its  nature  absorb  certainly 
more  than  its  bulk  of  oxygen.  From  the  evolutionary  viewpoint  it  has 
been  evolved  for  the  sole  purpose  of  carrying  a  large  amount  of  this  gas 
from  the  lungs  to  the  tissues,  for  taking  it  readily  and  rapidly,  and  for 
giving  it  up  quickly  and  easily.  Hemoglobin  is,  in  fact,  an  excellent 
example  of  a  substance  developed  to  a  high  perfection  apparently  for  a 
single  purpose.  The  hemoglobin  of  animals  and  the  chlorophyll  or 
plant-green  of  the  vegetable  kingdom  are  very  similar  chemically,  if 
not  identical  in  their  composition,  and  their  functions  are  certainly 
homologous. 

The  place  and  condition  of  the  carbon  dioxide,  while  it  is  being  excreted 
from  the  protoplasm  into  the  lungs  by  the  blood, are  not  so  easily  described 
as  are  these  same  matters  in  regard  to  oxygen.  The  former  gas  is 
carried  apparently  by  the  leukocytes,  the  erythrocytes,  and  the  plasma, 
two-thirds  of  it  being  contained  in  the  last  of  these.  While  it  is  true  that 
blood -plasma,  owing  to  the  presence  of  indifferent  substances,  cannot 
hold  in  simple  solution  as  much  of  any  gas  as  water  can,  still  plasma 
holds  much  more  of  carbon  dioxide  than  of  oxygen.  Setschenow  calcu- 
lated that  of  the  carbon  dioxide  in  the  dog's  serum,  one-tenth  was  in 
simple  solution  in  the  liquid.  Most  of  this  gas  in  the  blood  is  undoubt- 
eflly  contained  in  the  plasma  rather  than  in  the  corpuscles.  It  is  in  two 
sorts  of  union  with  the  various  chemicals  of  the  plasma — namely,  in  loose 
and  in  firm  chemical  combination.  These  distinctions  are  purely  empir- 
ical, the  portion  in  loose  combination  being  removable  with  a  vacvnim, 
but  not  that  in  firm  combination.  Bunge  by  analyzing  out  the  sodium 
content  of  dog's  serum,  calculated  that  a  liter  of  such  plasma  could  hold 
682  c.c.  in  ehemieal  union,  or  63.2  volumes  per  cent.  Most  of  the  carbon 
dioxide  of  the  plasma  is  in  combination  with  those  dissolveel  salts  that 


RESPIRATION  115 

render  the  plasma  alkaline — namely,  sodium  carbonate  and  sodium  phos- 
phate. Walter  found  in  the  blood  of  rabbits  poisoned  with  hydrochloric 
acid  (thus  rendering  the  plasma  acid) only  2.5  volumes  percent,  of  carbon 
dioxide.  According  to  Fernet  and  to  Heidenhain,  tiie  dioxide  is  also 
combined  in  part  with  sodium  acid  phosphate,  XajHPO^,  but  only  to  a 
small  extent.  Serum  globulin  is  another  substance  of  the  plasma  which 
undoubtedly  holds  some  of  the  carbon  dioxide  during  its  transit  to  the 
lungs.  The  corpuscles  contain  about  a  third  of  the  carbon  dioxide, 
it  being  "in  loose  chemical  combination  probably  with  the  alkali  of  the 
phosphates,  globulin,  and  hemoglobin  of  the  corpuscles,  and  directly 
with  the  hemoglobin."  (Starling.)  Setschenow  found  in  the  erythro- 
cytes 10  per  cent,  by  volume  of  carbon  dioxide  and  in  the  leukocytes 
2.5  per  cent. 

There  is  a  small  amount  (about  1.8  per  cent.)  of  nitrogen  simply 
dissolved  in  the  blood,  but  as  it  appears  not  to  have  any  respiratory 
function,  its  further  consideration  need  not  detain  us.  It  is  absorbed 
by  the  blood  in  the  lungs  on  purely  physical  principles,  and  does  not 
enter  into  chemical  combination  when  in  its  iree  gaseous  state,  being 
only  a  diluent  of  the  oxygen  of  the  atmosphere. 

Having  summarized  now  the  chemical  information  as  to  the  relation 
of  the  respiratory  gases  in  the  blood  to  and  from  the  lungs  and  the 
tissues,  let  us  see  in  general  terms  the  mechanism  of  this  transit. 

The  blood  circulating  in  its  closed  system  of  tubes  and  transuding 
(as  lymph)  through  the  capillary  walls  is  the  means  of  the  distribution 
of  oxygen  and  of  the  excretion  of  the  carbon  dioxide  into  air  in  the  alveoli. 
As  the  arterial  blood-current  moves  a  meter  or  less  in  a  second,  and  the 
venous  current  somewhat  more  slowly  (the  capillaries  are  only  ^  mm. 
long),  a  complete  circulation  from  any  point  through  the  heart  and  the 
lungs  and  back  again  to  the  point  of  starting  might  occur  in  thirty  seconds. 
This  fact  shows  how  prompt  a  carrier  the  blood  (plasma  and  corpuscles) 
is,  and  as  it  is  a  continual  flow,  unceasing  for  an  instant  during  life,  the 
service  is  very  efficient.  Owing  to  the  minute  caliber  of  the  capillaries 
of  the  lungs  and  tissues  generally,  the  speed  of  the  blood  through  them  is 
small,  h  mm.  per  second.  The  capillaries  average  ^  mm.  in  length,  and 
there  is  just  a  second,  therefore,  on  the  average,  for  the  plasma,  its  dis- 
solved sodium  carbonate  and  phosphate,  and  the  two  main  sorts  of 
corpuscles  floating  in  its  stream  to  dissolve  and  absorb  from  the  lungs 
their  load  of  oxygen  and  from  the  tissues  their  load  of  carbon  dioxide. 
During  this  second  also  the  respective  burdens  must  be  dropped  when 
they  have  made  their  transits. 

The  structures  through  which  the  two  respiratory  gases  pass  in  internal 
respiration — that  is,  between  the  tissue-capillaries  and  the  interior  of 
tissue-cells — are  not  imlike  the  homologous  structures  of  external  respira- 
tion in  the  lungs.  A  molecule  of  oxygen  bound  from  the  blood  for  a 
tissue-cell  must  pass  through  the  plasma  intervening  between  the  red 
corpuscle  from  which  it  starts  and  the  capillary  wall;  through  the 
endothelium  constituting  the  latter;  through  a  layer  of  lymph,  prac- 


116  RESPIRATION 

tically  plasma,  outsule  the  capillary;  through  the  cell's  wall,  if  it 
has  one;  and  then  through  a  larger  or  smaller  layer  of  protoplasm  into 
the  interior  of  the  cell.  All  these  are  either  liquid  or  semiliquid  pro- 
toplasm, and  hence  each  offers  a  minimum  resistance  to  the  progress  of 
the  two  respiratory  gases.  As  is  the  case  with  the  mechanism  of  external 
respiration  also,  these  tissues  together  constitute  an  animal  membrane, 
in  reality  complex  both  structurally  and  probably  functionally.  Yet 
this  may  be  considered  as  a  simple  membrane  in  studying  the  forces  and 
other  conditions  which  determine  the  passage  through  it  of  the  oxygen 
and  the  carbon  dioxide.  What  the  different  layers  of  this  living  partition 
between  the  blood  and  the  tissues  have  to  do  with  this  transit  of  the  two 
gases  is  at  present  undetermined.  We  can  study  it  only  as  a  whole,  and 
even  then  the  precise  functional  conditions  are  none  too  certain. 

The  Sequence  and  the  Causes  of  the  Respiratory  Events. — Let  us  now 
systematically  trace  an  imagined  portion  of  oxygen  from  the  atmosphere 
inward  to  some  tissue-cell  and  a  portion  of  carbon  dioxide  outward  from 
a  cell  to  the  open  air.  We  will  note  in  the  progress  the  process  itself  and 
the  causes  which  bring  it  about;  we  will  see  what  actually  happens  to 
and  about  the  supposed  molecules  of  oxygen  and  of  carbon  dioxide  as 
they  pass  in  and  out  respectively.  By  "causes"  we  here  may  understand 
the  physical  and  chemical  forces  which  combine  to  produce  the  orderly 
sequence  of  respiration.  This  viewing  of  the  events  in  order  will  serve 
at  once  to  make  the  actual  process  clear  and  to  summarize  the  facts 
already  stated  of  its  mechanism  and  chemistry.  The  description  of  these 
events  naturally  divides  into  two  parts,  the  course  and  the  causes  of  the 
movements  of  the  two  respiratory  gases  respectively. 

The  Course  axd  the  Kinetics  of  the  Oxygen  Inward. — Pressing 
in  all  directions  at  the  nostrils  is  the  atmosphere  under  a  pressure  of  about 
1032  grams  on  every  square  centimeter  of  surface.  This  is  the  weight  of 
a  column  of  the  atmosphere  of  that  size  many  miles  high  above  us. 
Thus,  gravity  is  the  force  which  causes  the  air  to  pass  inward  in  inspira- 
tion. Before  entrance  can  be  made,  however,  space  has  to  be  provide<l 
for  it  to  move  into.  This  space  is  furnished,  as  we  have  seen,  at  the 
expense  of  crowding  downward  the  abdominal  viscera,  the  distending 
of  the  abflominal  walls,  and  by  an  enlargement  of  the  thorax  forward, 
upward,  and  laterally,  as  well  as  downward.  The  mechanism  of  this 
enlargement  produced  by  muscular  contraction  has  already  been  sug- 
gested . 

As  anyone  at  all  familiar  with  the  thoracic  viscera  realizes,  however, 
the  matter  is  not  in  its  physics  so  simple  as  this.  The  thorax  is  not  a 
space  V)Ounded  by  elastic  walls  which  expand  and  so  enlarge  the  "cavity 
of  the  thorax."  The  only  variable  cavities  in  the  thorax  connected  with 
respiration  are  those  minute  spaces  contained  within  the  complicated 
and  highly  elastic  lungs — namely,  the  alveoli  and  the  terminations  of  the 
numerous  bronchi.  Moreover,  nearly  surrounding  the  lungs  are  the 
pleura",  and  these  are  reflexed  so  as  to  line  not  only  the  outer  surface  of 
the  limgs,  but  also  the  inner  surface  of  the  thoracic  wall  proper.    Thus, 


RESPI  RATIOS'  117 

between  the  outer  surface  of  the  hmg  and  the  thoracic  wall  on  each 
side  is  the  so-called  "pleural cavity."  Physiologically  speaking,  this 
is  a  misleading  misnomer.  Each  of  the  pleurae  is  a  sac,  one  of  whose 
sides  lines  the  ribs  and  intercostal  muscles,  while  the  other  encloses  a 
lung.  It  is  only  because  this  sac  is  completely  close<l,  air-tight,  that  the 
thoracic  wall  on  expanding  outward  does  not  draw  apart  its  two 
sides  and  leave  the  lung  unenlarged.  Boys  sometimes  amuse  them- 
selves with  a  scientific  toy  made  of  a  circular  piece  of  stout  leather 
five  or  six  inches  in  diameter,  through  the  center  of  which  is  knotted 
a  strong  string.  The  leather  being  wet  and  pressed  carefully  over 
the  smooth  surface  of  a  boulder,  a  considerable  rock  can  be  lifted  by 
drawing  upward  on  the  string.  Theoretically  about  as  many  pounds 
of  rock  can  be  raised  as  there  are  square  inches  of  leather  multiplied, 
by  14.7,  which  is  the  weight  in  pounds  of  the  atmosphere  over  a  square 
inch  of  this  sucker.  The  boy's  muscles  lift  the  rock,  but  the  weight 
of  the  air  keeps  the  leather  meanwhile  in  contact  with  the  stone. 
Exactly  so  in  inspiration:  the  muscles  (external  intercostals  chiefly) 
horizontally  enlarge  the  thorax,  but  the  atmospheric  pressure  keeps 
the  outer  surface  of  the  hmgs  in  contact  with  the  expanding  thoracic 
wall,  thus  distending  the  lungs  against  their  elasticity.  Thus,  two 
forces  combine  to  draw  the  air  through  the  nostrils  and  into  the 
larger  bronchi,  muscular  contraction  providing  space  into  which  the 
atmosphere  is  forced  by  its  own  w^eight  (gravitation). 

The  essential  importance  of  the  air-tightness  of  the  pleural  cavities, 
so-called,  is  demonstrated  only  too  often  by  accidents  to  people  in 
which  the  pleural  sac  is  punctured  in  a  way  that  the  tissues  cannot 
immediately  close.  By  a  bullet,  a  dagger,  or  a  corroding  ulcer,  air 
is  let  into  a  pleural  "cavity" — which  then  for  the  first  time  becomes 
a  real  cavity.  The  elasticity  of  the  lung-tissue  now  draws  together 
the  lung  in  a  collapsed  condition,  and  it  no  longer  enlarges  in  inspira- 
tion, no  longer  ventilates.  The  two  surfaces,  visceral  and  parietal, 
of  the  pleura  are  drawn  apart  and  separated  by  air  instead  of  by  a 
mere  lubricating  layer  of  lymph  or  plasma  such  as  alone  is  present 
in  the  uninjured  animal.  If  inflammation  does  not  occur  the  opening 
in  the  thoracic  wall  soon  heals  together,  the  air  in  the  cavity  is 
absorbed  by  the  tissues,  and  the  lung  gradually  resumes  its  bellows-like 
expansion  and  contraction  and  its  normal  functions.  If  both  pleural 
"cavities"  are  punctured,  and  skilled  and  unusual  means  be  not  close  at 
hand,  the  patient  promptly  dies  of  asph\'xia,  both  lungs  being  then 
undilatable.  This  is  the  condition  known  in  surgery  as  pneumothorax, 
single  and  double  respectively. 

The  force  which  causes  the  oxygen  of  the  bronchial  tidal  air  to 
continue  its  course  to  the  alveoli  on  its  way  to  the  capillary  blood 
there,  seems  to  be  an  addition  to  this  the  physical  force  of  diffusion.  In 
respiration  this  force  may  be  said  to  be  the  preeminent  physical  prin- 
ciple, if  the  term  be  used  to  include  osmosis,  the  passage  through  a 
membrane.     The  diffusion   of    gases   is   that   process  by  which    two 


lis  RESPIRATION 

gases  which  tlo  not  chemically  interact  mix  into  a  homogeneous  mass 
when  brought  together.  Thus,  if  a  large  bottle  be  half-filled  with 
carbon  dioxide  and  then  the  upper  half  filled  with  hydrogen,  in  a  short 
time  the  bottle  will  contain  a  homogeneous  mixture,  although  the 
carbon  dioxide  is  many  times  heavier  than  the  hydrogen.  Again,  if 
one  bottle  be  filled  with  oxygen,  a  tube  1  meter  long  and  only  1  cm.  in 
diameter  connected  with  it  and  inserted  into  a  similar  bottle  above 
containing  hydrogen,  in  a  few  hours  both  bottles  will  contain  a  homo- 
geneous mixture  of  the  hydrogen  and  oxygen,  although  the  light  hydro- 
gen has  to  pass  downward  through  a  narrow  tube  in  doing  its  part 
of  the  diffusion.  This  phenomenon  is  brought  about  by  the  fact  that 
the  molecules  of  gases  are  continually  and  rapidly  moving  in  straight 
lines  as  far  as  they  can  go — namely,  until  they  meet  with  obstacles, 
whether  other  molecules  or  the  walls  of  the  vessel  containing  the  gas. 
As  the  rate  of  the  molecular  movements  of  a  gas  increases  with  its 
temperature,  diffusion  takes  place  faster  in  a  warm  environment,  e.  g., 
in  the  lung,  than  in  cool  surroundings.  The  rate  varies  also  with  the 
density  of  the  gases,  in  exact  terms  inversely  as  the  square  root  of  the 
density  (Graham's  law).  If  a  vessel  be  filled  with  oxygen  and  hydrogen 
each  on  one  side  of  a  porous  and  thin  earthenware  partition  dividing 
the  vessel  equally,  the  two  gases  will  pass  through  this  diaphragm  at 
very  different  rates;  4  c.c.  of  hydrogen  will  work  its  way  through  the 
pores  of  the  earthenware  and  into  the  other  half  of  the  vessel  while 
1  c.c.  of  oxygen  is  passing  in  the  opposite  direction.  This  process 
of  admixture,  whether  or  not  through  a  dry  partition,  is  diffusion,  and 
is  the  process  in  part  which  obtains  in  the  small  bronchi  of  the  lungs. 
It  must  be  discriminated  carefully  from  the  phenomena  which  occur 
when  gases  mix  through  an  organic  membrane,  such  as  one  made  of 
skin,  rubber,  or  epithelium;  the  process  then  is  osmosis.  In  diffusion 
there  is  immediate  mixture  or  else  the  passage  of  the  gases  through 
minute  tubes  such  as  those  of  the  earthenware  partition  or  the  smallest 
bronchi,  the  conditions  being  relatively  simple.  In  gaseous  osmosis,  on 
the  other  hand,  the  rate  of  interchange  depends  not  alone  on  the  natures 
of  the  passing  gases  and  their  passageways,  but  more  on  the  nature  of 
the  dividing  membrane.  Among  the  determining  factors  in  osmosis  are 
the  relative  diffusibilities  of  the  two  gases:  their  respective  densities; 
the  different  degrees  exerted  by  the  membrane  on  the  different  gases  by 
virtue  of  which  the  gas  which  aflhcres  the  most  strongly  penetrates  the 
diaphragm  most  easily;  and  the  degree  of  actual  liquefaction  of  the  two 
gases  sometimes,  which  may  thus  penetrate  the  membrane  and  evap- 
orate to  gases  again  on  the  other  side.  Osmosis  is  the  process  which 
obtains  in  external  and  internal  respiration.  The  "membrane"  in 
this  case  is,  of  course,  the  complex  and  protoplasmic  epithelial  layers 
of  the  alveolar  wall  and  that  of  the  capillaries,  plus  the  layers  of  inter- 
vening organic  liquid,  already  described. 

The  Course  and  the  Kinetics  of  the  Carbon  Dioxide  Outward. 
— This  can  be  flescribed  much  more  briefly  than  was  the  corresponding 


RESPIRATION  119 

treatment  of  the  oxygen,  because  these  two  homologous  series  of  events 
are  very  similar  in  their  natures,  and  only  their  differences  need  to  be 
noted. 

On  an  average,  the  partial  pressure  of  carbon  dioxide  in  the  tissues 
is  about  58  mm.  of  mercury,  while  in  arterial  blood  it  is  not  much  over 
21  mm.  Because,  therefore,  arterial  blood  practically  saturates  the 
tissues  everywhere,  the  carbon  dioxide,  poured  out  unceasingly  by  the 
tissue-protoplasm,  takes  this,  the  path  of  least  resistance.  It  goes 
through  with  a  pressure  represented  by  the  difference  of  these  numbers, 
37  mm.  of  mercury.  Thus,  it  passes  everywhere  into  the  capillary 
blood,  which  is  thereby  made  venous.  Here,  again,  the  process  per- 
haps is  one  combined  of  osmosis,  chemical  affinity,  solution,  and 
secretory  selection,  and  thereby  the  carbon  dioxide  passes  into  the 
plasma  of  the  blood  and  into  the  leukocytes  in  proportions  already 
described.  The  blood  is  constantly  streaming  backward  from  all  direc- 
tions to  the  right  auricle,  whence  when  pumped  by  the  right  ventricle  it 
is  hurried  into  the  pulmonary  capillaries.  There  it  becomes  revitalized 
by  the  acquisition  of  more  oxygen  and  the  giving  up  of  its  large  burden 
of  w'aste  carbon  dioxide.  The  deliverance  of  this  latter  gas  occurs 
partly  doubtless  on  the  same  familiar  principles.  Sometimes,  at  least, 
the  living  protoplasmic  membrane  separating  it  from  the  air  aids  and 
actively  draws  and  pushes  it  through.  It  goes  partly,  too,  because  the 
tension  of  carbon  dioxide  in  the  venous  blood  of  the  capillaries  is  about 
41  mm.  of  mercury,  while  that  of  the  alveoli  is  only  29.  Gases,  like 
w'ater,  always  tend  to  run  down  the  hill  of  the  gradient  of  pressures,  to 
take  the  path  of  the  lesser  resistance.  Such  is  the  adaptation  of  the 
respiratory  protoplasm,  however,  that  in  case  the  pressure-gradient 
declines  in  the  direction  prejudicial  to  the  life  of  the  animal,  there  are 
automatic  means,  already  noted,  of  forcing  the  carbon  dioxide,  so  to 
say,  up  hill  in  the  life-preserving  direction.  In  more  direct  terms,  the 
lung-epithelium  draws  the  gas  out  of  the  blood  and  thus  out  of  the 
organism.  The  metabolism  of  plants  may  then  make  it  over,  liberating 
its  oxygen  for  animals  to  breathe  again. 

The  progress  from  the  alveoli  to  the  tidal  air-current  in  the  larger 
bronchi  occurs  under  simpler  conditions.  It  is  caused  partly  by  gaseous 
diffusion,  partly  by  muscular  contraction  of  the  bronchioles,  and  partly 
by  the  compression  of  the  lungs  by  the  heart  each  time  it  expands  in 
diastole.  That  diffusion  is  an  active  agent  of  this  transfer  may  be  seen 
from  the  differences  in  partial  pressures  of  the  carbon  dioxide  in  the 
alveoli  (about  29  mm.  of  mercury)  and  that  in  the  open  air  (not  over 
0.3  mm.).  This  pressure-gradient,  combined  wdth  that  of  the  oxygen 
opposed  (159  mm.  to  100  mm.)  sets  up  two  streams  in  opposite 
directions,  and  keeps  the  excreting  carbon  dioxide  pouring  outward 
into  the  larger  bronchi.  There,  as  part  of  the  expiratory  tidal  air,  it  is 
forced  out  through  the  trachea,  larynx,  nares,  and  nostrils  seventeen 
times  or  so  every  minute. 

The  expiratory  process,  already  described,  is  largely  in  normal  respi- 


120 


RESPIRATION 


ration  a  passive  one.  It  is  a  complex  movement  of  recoil  in  tissues 
variously  stretched,  twisted,  displaced,  or  bent,  and  of  the  fall  of  more  or 
less  heavy  tissues  raised,  by  the  active  muscular  movements  of  inspira- 
tion. All  of  these  strains  together  force  the  tidal  air,  500  c.c.  at  a  breath, 
upward  and  outward.  The  expiratory  movement  follows  the  com- 
pletion of  the  inspiratory  movement  normally  without  appreciable  pause. 
Expiration  requires  normally  one-fifth  more  time  than  does  inspiration. 
The  pressure  of  the  air  in  the  trachea  during  expiration,  according  to 
Bonders,  is  about  2  mm.  of  mercury,  which  may  be  increased  in  forced 
expiration  to  100  mm.  As  the  air  passes  upward  the  larynx  rises  slightly, 
raised  partly  by  the  expanding  lungs  and  partly  as  the  effect  of  contrac- 
tion of  the  thyrohyoid  muscles. 

Fig.  67 


The  Anolis  stethograpli:  the  padded  arms  of  the  levers  at  A  and  B  partly  enclose  the  cha- 
meleon, mouse,  or  other  vertebrate  of  proper  size  (fixed  by  its  legs  to  the  frog-board),  just 
behind  its  forelegs;  C  is  the  thread  by  which  the  respiratory  movements  are  conveyed  to  a  light 
aluminum  lever  for  record  on  the  smoked  kymograph-drum. 


The  Respiratory  Rliythm. — One  of  the  most  conspicuous  elements 
in  both  the  bfxlily  movements  and  the  sensation-mass  of  man  is  the 
rhythmic  rise  and  fall  of  the  chest  walls  in  respiration.  We  have  already 
considered  the  probable  cause  of  this  complicattxl  system  of  movements, 
finding  that  it  is  regulated  by  a  compound  center  in  the  medulla, 
which  is  in  turn  actuated  by  certain  lacks  or  excesses  in  the  constituents 
of  the  capillary  blood  flowing  through  it.  There  are  certain  elements 
in  the  rhythm  itself  which  are  of  scientific  interest  and  practical  impor- 
tance. Among  these  are  its  time-relations  and  its  rate  under  various 
organic  conditions.  Many  researc-hcs  have  been  carried  out  on  men, 
as  well  as  on  animals,  in  the  study  of  the  res])iratory  rhythm  and  its 
derangements.  One  methrxl  of  registering  these  movements  is  by  means 
of  the  pneumograph  devised  by  Marey  and  improved  by  Fitz.    By  the 


RESPIRATION 


121 


Fig.  68 


use  of  this  instrument  pneumatic  negative  pressure  actuates  the  lever 
of  a  recording  tambour.  Another  apparatus  for  recording  the  time- 
relations,  etc.,  of  the  respiratory  rhythm  is  the  stethograph,  a  variety 
of  which  adapted  to  study  the  respiratory  movements  of  the  common 
Southern  hzard  Anohs  ("chameleon")  is  shown  in  Fig.  67.  It  con- 
sists of  levers  resting  against  the  sides  of  the  thorax  of  the  little  animal, 
which  when  separated  lift  a  light  lever  writing  as  before  on  a  smoked 
drum  rotating  by  clockwork.  A  third  way  of  studying  the  respiratory 
rhythm  is  to  record  by  means  of  levers  as  before  the  movements  up 
and  down  of  the  reservoir  which  receives  the  air  expired  by  the  animal. 
This  is  perhaps  the  least  useful  of  the  methods  so  far  devised,  for  the 
reason  that  the  conditions  are  complicated  by  chemical  as  well  as  by 
merely  mechanical  relations.  The  last  of  the  methods  invented,  and 
one  which  has  told  us  much  concerning  the  respiration  of  the  smaller 
mammals  and  of  the  movements 
of  the  diaphragm  especially,  is 
that  of  Head,  who  employed  slips 
of  the  rabbit's  diaphragm  to  di- 
rectly actuate  levers  recording  as 
before  described. 

By  these  means,  and  by  others 
more  or  less  similar,  the  chief 
characteristics  of  the  gross  re- 
spiratory movements  have  been 
accurately  studied.  It  has  been 
learned  that  in  man  the  time  of 
inspiration  is  shorter  than  that 
of  expiration,  the  former  being 
to  the  latter  about  as  6  to  7.  In 
women,  children,  and  old  people 
the  difference  is  greater  than  this. 
There  is  normally  no  pause  be- 
tween the  cessation -of  inspiration 
and  the  commencement  of  ex- 
piration, for  the  parts  put  on  stretch  instantly  recoil  in  their  various 
ways  when  the  active  contractile  pressure  stops  at  the  end  of  inspiration. 
Between  the  end  of  one  expiration  and  the  beginning  of  the  next  in- 
spiration there  is  normally  a  short  pause.  In  duration  this  may  be 
about  one-fifth  of  the  time  required  for  a  complete  respiration.  Ob- 
servation of  any  normal  stethogram,  for  examplie,  that  of  Fig.  68,  shows 
well  the  respective  characteristics  of  the  inspiratory  and  of  the  expiratory 
movements.  The  inspiratory  phase  is  at  first  quick  (as  is  shown  by  the 
nearly  vertical  direction  of  the  tracing),  and  then  slightly  slows  to  its 
end ;  it  is  also  steady  and  interrupted  less  often  than  is  the  expiratory 
phase.  The  expiratory  movement  is  somewhat  slower  and  more  variable 
in  its  dift'erent  parts,  as  is  shown  by  the  tracing's  obliquity  and  relative 
irregidarity.     In   looking  over  a  number  of    stethograms    traced   from 


The  Anolis  stethogram.  This  shows  one  type 
of  the  breath-movements  of  the  common 
Southern  "chameleon."  The  right-hand  line  in 
each  curve  is  the  inspiratory  movement.  To  be 
read  from  right  to  left.  Original  .size.  The 
time-line  is  in  seconds.  (See  other  Anolis  stetho- 
grams in  the  Appendix.) 


122  RESPIRATION 

different  animals,  these  qualities  would  be  much  more  emphatically 
noticed  than  in  that  of  the  figure  made  from  Anolis. 

The  respiratory  movements,  except  so  far  as  stopping  them  for  a  long 
time  is  concerned,  are  very  perfectly  under  the  control  of  the  animal's 
will.  This  we  shall  see  more  fully  in  studying  speech.  Thus,  stetho- 
grams  have  many  more  arbitrary  interruptions  in  their  course  than 
have,  for  example,  sphygmograms,  or  tracings  made  from  the  pulse 
of  the  heart,  which  is  only  rarely  under  voluntary  control.  Men  by 
practice  can  learn  to  stop  their  breathing  for  five  minutes  or  so,  as  do- 
the  pearl-  and  sponge-divers  of  the  South  Sea  islands.  No  man  can 
commit  suicide  by  this  means,  however,  unless  it  be  those  rare  indi- 
viduals who  have  some  voluntary  control  of  their  hearts  and  respiration 
together.  In  this  case  death  is  caused  by  stopping  for  too  long  a  period 
the  heart  rather  than  the  respiratory  mechanism. 

The  relation Hbetween  these  two  rhythms,  the  cardiac  and  the  respira- 
tory, is  close  and  tends  to  keep  up  the  ratio  of  4  to  1,  whatever,  within 
limits,  be  the  condition  of  either  rhythm.  As  the  breath-rate  goes 
high,  as,  for  example,  in  pneumonia,  the  pulse-rate  oftentimes  fails  to 
keep  up  this  its  normal  ratio. 

The  Breath-rate. — Few  things  in  human  function  are  more  normally 
variable  within  normal  limits  than  is  the  number  of  respirations  per 
minute.  The  reason  for  this  is  that  respiration  is  more  closely  related 
to  other  functional  conditions  and  more  sensitive  to  mental  influence 
than  almost  any  other  of  the  basal  functions.  This  may  in  turn  be 
due  to  the  wide  and,  indeed,  almost  universal  connections  of  the  vagus, 
the  nerve  which  has  so  much  to  do  with  respiration. 

The  breath-rate  varies,  for  example,  according  to  sex,  age,  season, 
time  of  day,  muscular  and  mental  activity,  temperature  of  the  air,  body- 
temperature,  recency  of  digestion,  volition,  atmospheric  pressure, 
emotion,  composition  of  inspired  air,  depth  of  breathing,  pulse-rate, 
sleep,  and  posture.  These  sixteen  or  seventeen  conditions,  at  least, 
besides  the  protoplasmic  structure  of  the  respiratory  central  neurones 
and  the  respiratory  state  of  the  blood,  determine  the  number  of  breaths 
per  minute  in  man. 

We  need  hardly  do  more  than  to  point  out  the  direction  in  which  each 
of  these  influences  acts.  Because  the  nervous  system  of  the  female  is 
more  unstable  than  that  of  the  male,  women  appear  to  breathe  often- 
times much  more  rapidly  than  do  men.  The  average  excess  is  really 
small,  and  in  childhood  nearly  nil;  indeed,  IMilne  Edwards  supposed 
that  young  men  breathe  somewhat  more  rapidly  than  young  women. 
On  the  average,  it  may  be  said  that  women  breathe  twice  or  thrice  a 
minute  more  than  do  men.  The  variation  according  to  age  is  large,  and 
of  much  practical  importance  in  nicflicine.  From  three  hundred  count- 
ings, Quetelet  flerived  the  following  numbers: 


RESPIRATION 

Variations  in  Breath-kate  with  Age 
Average  Number  of  Respirations  per  Minute. 


123 


Years  of  age. 

Respirations.       1 

Years  of  age. 

Respirations. 

0  to    1 

1  to    5 
15  to  20 

44 
26 
20 

20  to  25 
25  to  30 
30  to  50 

18.7 
16.0 
18.1 

Season  of  the  year  has  a  distinct  influence,  the  rate  being  greater 
in  spring  than  in  fall.  The  variation  according  to  the  hour  of  the  day 
nearly  follows  that  of  the  pulse,  the  breath-rate  being  less  at  night,  when 
metabolism  is  also  less.  ^Muscular  exertion  has  very  marked  influence 
on  the  rate,  respiration  being  more  sensitive  even  than  the  circulation, 
and  hastening  sooner  after  the  exercise  begins.  Only  a  very  small 
increase  in  the  muscular  exertion  is  required  to  distinctly  accelerate 
the  breathing,  the  stimulation  being  due  probably  to  excitation  of  the 
center  by  acid  products  of  muscular  activity.  Mental  exercise  has  a 
similar  eft'ect,  but  less  in  amount;  respiration  is  apt  to  be  inhibited 
more  or  less  and  made  irregular  by  many  sorts  of  mental  activity.  The 
influence  of  atmospheric  temperature  is  slight,  but  a  rise  of  the  tempera- 
ture somewhat  lowers  the  rate.  Body-temperature,  on  the  other  hand, 
is  of  marked  influence  on  the  respiratory  rate,  a  matter  of  clinical 
and  diagnostic  importance.  Thus,  fever  from  whatever  cai\se  increases 
the  rate,  while  in  coma  and  in  collapse  the  rate  is  lessened.  The  process 
of  digestion  slightly  increases  the  breath-rate,  especially  dinner  at  noon 
(Merordt),  the  increase  being  apparently  due  to  the  forced  increase  in 
metabolism  due  to  the  temporary  feeding  of  the  blood.  The  will,  of 
course,  has  great  influence  over  the  rate,  for  we  can  breathe  more 
rapidly  than  normally,  if  we  so  choose,  until  the  inspiratory  muscles 
become  too  painful  or  exhausted.  Likewise  we  can  breathe  more 
slowly  than  normally,  provided  we  breathe  more  deeply.  x\tmospheric 
pressure  exerts  little  influence  unless  excessive,  in  which  case  greater 
pressure  decreases  the  rate  and  rarefaction  increases  it.  This  is  in 
order  that  the  respiratory  ventilation  may  remain  the  more  nearly 
constant.  Dwellers  on  high  mountains  breathe  faster  than  do  persons 
on  the  sea  level.  The  various  emotions  have  characteristic  influences 
on  the  breath-rate,  some  hastening  it  and  some  slowing  it.  In  general 
the  sthenic  or  strength-giving  and  pleasant  emotions  quicken  the  rate, 
W'hile  the  asthenic  and  unpleasant  emotions  retard  it.  If  the  air  to  be 
breathed  becomes  deficient  in  oxygen  (below  13  per  cent,  by  volume) 
or  excessive  in  carbon  dioxide,  the  breath-rate  is  increased  to  restore  the 
normal  conditions  in  the  body.  The  rate  of  breathing  is  in  inverse  ratio 
to  the  depth  of  breathing.  This  is  conspicuous  in  pneumonia,  for 
example,  in  which  case  parts  of  the  hmgs  may  be  thrown  out  of  their 
function.  As  has  been  said  before,  the  respiratory  rate  tends  to  keep  a 
constant  ratio  of  1  to  4  with  the  pulse-rate,  save  in  fever  and  other  abnor- 
mal conditions.  On  this  account  conditions  which  affect  directly  only 
the  frequency  of  the  heart  often  indirectly  increase  the  breath-rate  also. 


124  RESPIRATIOX 

In  sleep,  because  the  metabolism  is  lessened,  the  rate  is  less;  the 
decrease  in  muscular  activity  during  sleep  probably  helps  the  effect. 
The  decrease  is,  on  the  average,  about  20  per  cent,  of  the  waking  rate. 
Finally,  posture  may  affect  the  rate  aside  from  the  variations  of  muscular 
exercise  in  the  different  postures.  In  standing,  the  respiration  is  faster 
than  in  sitting,  and  faster  in  sitting  than  in  lying  down.  This,  perhaps, 
is  due  to  mechanical  interference  with  the  depth  of  the  inspirations, 
which,  as  we  noted  above,  increases  the  rate. 

The  breath-rate  varies  widely  in  different  animals,  and  a  tabulation  of 
the  rates  of  many  genera  gives  little  clue  to  the  reason  for  some  of  the 
variations. 

Breath-rates  of  Various  Animals  (Bert). 

Complete  Respirations  per  Minute. 

Hippopotamus     ....        I  Panther 18 

Snake 5  Canary IS 

Tiger 6  Cat     " 24 

Condor 6  Pigeon .30 

Rhinoceros  .      .      .   6  to  10  MoUusca   .      .  14  to  65 

Ass 7  Perch 30 

Giraffe 8  to  10  Hippocampus       ....     33 

Lion 10  Raja 50 

Jaguar 11  Eel 50 

Dromedary 11  Torpedo 51 

Horse 10  to  12  Rabbit 55 

Tortoise 12  Mullet 60 

Crab 12  Sparrow 90 

Dog 15  Siskin 100 

Ox 15  to  18  Rat  (asleep) 100 

Man IS  Rat  (awake)    .      .      .     up  to  210 

Why  the  rhinoceros  should  breathe,  say,  eight  times  as  often  as  the 
hippopotamus,  or  the  sparrow  five  times  as  frecjuently  as  the  canary,  it  is 
difficult  to  satisfactorily  explain.  The  physiology  of  other  differences  is 
"obvious,  and  leads  to  rather  fundamental  considerations  of  importance. 
The  most  basal  criterion  of  difference  is  probably  that  of  difference  in 
degree  of  the  body-metabolism  based  either  on  difference  in  the  activity 
of  the  animal  or  on  its  size.  Moreover,  the  heat  lost  is  determined 
largely  by  surface  in  ratio  to  mass,  or  as  square  to  cube,  which,  of 
course,  gives  the  smaller  animal  the  larger  proportional  surface,  and  so 
the  larger  proportional  loss  of  energy.  More  oxygen  is  needed  to  cor- 
respond to  this  additional  metabolism.  The  same  explanation  probably 
applies  to  the  flifference  in  the  respiratory  ratio  of  the  cat  and  the  tiger, 
two  felines  much  alike  .save  in  size.  The  difference  in  rate  of  the  rat's 
breathing  and  in  tliat  of  the  tortoise  is  largely  one  of  metabolism,  arising 
from  inherent  differences  in  habits  and  nature,  the  rat  being  active  and 
homothermous,  the  tortoise  "cold -blooded"  and  proverbially  slow.  In 
general  the  breath-rates  of  the  birds  arc  liigh  because  of  their  liA^ely 
metabolism,  which  is  dependent  in  inrn  on  their  great  bodily  activity. 
In  the  ca.se  of  the  condor,  however,  a  bird  at  once  large  and  lazy,  we 
.see  a  very  low  rate,  on  the  principles  already  suggested. 

Special  Functions  Connected  with  Respiration. — 'J'here  are  a  number  of 
foiiiplcv  pi'occssrs,  vari(;usly  useful,  and   more  or  less  normal,  which 


RESPIRATION  125 

involve  the  respiratory  mechanism  more  than  that  of  any  other  func- 
tional system.  These  are,  among  others,  speaking,  singing,  coughing, 
sneezing,  hawking,  sniffing,  yawning,  sighing,  laughing,  sobbing,  snoring, 
sucking,  and  hiccoughing,  thirteen  functions  less  formidable  to  under- 
stand than  one  might  fear.  The  first  two  are  so  important  and  complex 
that  they  require  special  discussion  in  the  proper  place  immediately 
below.  The  next  four — coughing,  sneezing,  hawking,  and  sniffing — are 
movements  habitual  to  many  mammals  for  the  purpose  of  clearing  the 
respiratory  passages  of  mucus  and  other  obstructions  and  irritants. 
The  next  one — yawning — is  a  mode  of  muscular  relief.  The  next 
three — sighing,  laughing,  and  sobbing — are  emotional  expressions.  The 
general  nature  and  the  purpose  of  the  next — sucking  and  snoring — are 
known  to  everyone.  Hiccoughing  alone  seems  to  be  strictly  abnormal. 
Here  we  need  discuss  only  two  of  these  processes. 

Coughing  is  an  essentially  protective  process  in  catarrhal  inflamma- 
tion of  the  respiratory  passages  and  useful  for  removing  from  them 
accidental  particles,  as  of  food.  When  both  vagus  nerves  are  cut  in  the 
neck,  the  afferent  impulses  to  coughing  are  cut  off,  and  the  animal 
usually  dies  in  a  few  weeks  or  months  from  foreign-body  pneumonia. 
Coughing  may  be  either  a  voluntary  action  or  one  reflexly  started. 
It  consists  first  of  a  very  deep  and  full  inspiration,  with  the  closure 
of  the  glottis,  followed  by  a  forced  expiration.  When  the  increasing 
pressure  in  the  larynx  is  sufficient  the  glottis  is  burst  open  and  the 
current  of  air  passing  violently  out  through  the  previously  opened  mouth 
tends  to  remove  the  irritating  substances.  Stirling  enumerates  eight 
sources  of  stimulation  of  reflexly  produced  coughs:  (1)  The  respiratory 
mucous  membrane,  especially  of  the  larynx,  the  afferent  impulses  of  the 
reflex  arc  going  in  over  the  vagus  and  the  superior  laryngeal.  Kohts 
determined  that  a  cough-stimulus  could  come  from  only  the  glottis  res- 
piratoria,  not  from  the  true  vocal  cords  nor  from  the  trachea  down  to  the 
bifurcation.  (2)  The  skin,  especially  of  the  upper  part  of  the  body,  a 
cold  draught  on  which  produces  a  congestion  of  the  air-passages,  which 
in  turn  excites  coughing.  (3)  The  external  auditory  meatus,  where  a 
foreign  body  may  start  impulses  inward  over  the  auricular  branch  of 
the  vagus.  (4)  The  mucosa  of  the  stomach,  the  afferent  nerves  being 
again  in  the  vagus.  (5)  The  costal  pleura  and  (Kohts)  the  esophagus. 
(6)  The  nose.  (7)  The  pharynx.  (8)  The  liver,  spleen,  and  generative 
organs  in  diseased  condition  when  pressure  is  applied  over  them. 

Sneezing  is  similar  to  coughing  save  that  the  blast  of  air  from  the 
trachea  passes  out  through  the  nose  instead  of  the  mouth,  the  latter  being 
tightly  closed.  Sneezing  is  much  more  reflex  than  is  coughing.  A  bright 
hght  even  may  occasion  a  sneeze.  The  remainder  of  these  subsidiary 
respiratory  processes  are  of  interest,  but  do  not  need  special  description. 

The  Respiratory  Sounds. — As  might  be  expected  in  a  process  where 
currents  of  air  rush  in  and  out  through  a  series  of  tubes  and  chambers 
more  or  less  obstructed  in  various  ways,  the  function  of  respiration  is 
accompanied  by  various  sounds.    These  are  audible  either  by  the  unaided 


126 


RESPIRATION 


ear  or  by  means  of  magnifying  instruments,  such  as  the  stethoscope  or 
phonendoscope.  Accompanying  normal  breathing  through  average 
respiratory  organs  is  a  set  of  sounds  called  by  the  diagnostician  "nor- 
mal." AYhen  either  the  function  or  the  organs  are  materially  altered  the 
sounds  also  are  changed  and  thus  become  valuable  means  of  diagnos- 
ticating and  locating  disease.    This  is  the  important  art  of  auscultation. 

Two  sounds  made  in  normal  breathing — bronchial  breathing  and 
vesicular  murmur — are  especially  important. 

Bronchial  breathing  is  the  sound  natural  to  the  passage  of  a  current 
of  air  over  imperfectly  vibrating  strings  within  a  tube.  It  is  caused  by  the 
rapid  movement  of  the  air  passing  through  the  glottis.  It  is  heard  during 
both  inspiration  and  expiration,  and  best  over  the  larynx  and  the  trachea. 


Fig.  69 


Bronchial 
(.Tubular  clement 
less  intense. ) 

Normal 


Cavernous  or 

loric. 


Pure  bronchial 


Broncho-Vesicular. 
{Conduction  of  bronchial 
element  by  increased 
Interstitial  tissue.) 


Exaggerated. 

{Compensatory 

emphysema.) 


Feeble  or  absent, 

(Actelcctasis  due 

to  plugging  of 

bronchi.) 


.Broncho-Vesicular, 


Diagram  of  the  modification  of  bieath-sound.s  as  heard  on  aus<-ultation.      (Le  Fevre.) 


It  can  also  be  distinguished  below  the  trachea,  but  not  unmixed  with 
sound  produced  in  the  lung-tissue  proper.  Between  the  scapulfe,  behind, 
it  is  somewhat  less  distinct  than  over  the  trachea.  The  pitch  of  bronchial 
respiration  is  high,  that  of  expiration  being  somewhat  higher  than  that 
of  inspiration.  The  intensity  is  about  equal  in  the  two  phases,  as  is  also 
the  duration. 

The  vesicular  murmur  is  so  called  because  it  is  largely  caused  by  the 
expansion  and  recoil  of  the  air-vesicles  or  alveoli,  complicated,  however, 
with  the  tubular  sounds  produced  in  the  bronchioles.  The  murmur  of 
the  inspiratory  phase  is  about  four  times  as  long  in  duration  as  that  of 
expiration,  graclually  increasing  to  a  maximum  and  decreasing  again 
by  degrees.  A  sliglit  pause  intervenes  between  the  sounds  of  the  two 
phases.     In  quiet  breathing  the  expiratory  murmur  may  be  difhcult  to 


RESPIRATION  127 

hear.  It  is  hard  to  describe  the  nature  of  this  sound,  and  its  descrip- 
tion is  not  necessary  when  the  sound  itself  is  so  readily  available.  It  is 
produced  by  the  friction  of  the  air  entering  the  alveoli  plus  the  slight 
crepitation  of  the  alternately  expanding  and  lessening  bronchioles  and 
alveoli.  It  may  be  heard  at  its  best  below  the  left  clavicle.  In  most  parts 
of  the  lungs  this  sound  is  mixed,  more  or  less  in  different  places,  with  the 
bronchial  sound. 

Nasal  sounds  of  various  sorts  are  to  be  heard  externally,  their  quality 
and  intensity  depending  on  the  configuration  of  the  nares  and  the  nasal 
cavities. 

The  various  abnorTnal  respiratory  sounds  are  of  extreme  importance 
to  the  clinician  in  the  diagnosis  of  the  diseases  of  the  chest,  throat,  and 
nose,  and  moreover,  have  much  physiological  interest  because  they  serve 
to  illustrate  and  to  emphasize  the  mechanical  conditions  both  in  the 
structure  and  the  function  of  the  whole  respiratory  tract  above  the  dia- 
phragm. For  the  technical  description  and  names  of  these  numerous 
abnormal  sounds  the  student  is  referred  to  the  special  works  on  physi- 
cal diagnosis.  We  here  look  briefly  only  at  a  few  abnormal  mechanical 
conditions  in  the  breathing  apparatus  from  which  the  sounds  arise. 
When  some  of  the  alveoli  and  bronchioles  are  filled  up  by  exudate,  as  in 
pneumonia,  the  respiratory  sounds  may  be  absent  altogether  from  that 
part  of  the  chest,  save  as  they  are  conveyed  from  elsewhere.  To  com- 
pensate for  such  diminution  in  the  acting  lung-tissue,  the  functioning 
portions  work  more  vigorously,  and  the  more  or  less  normal  sounds  are 
increased  beyond  the  normal  intensity  ("puerile  breathing").  This 
comes  also  from  collapse  or  compression  of  a  lung,  as  in  empyema, 
pneumothorax,  or  pleurisy  with  effusion. 

Sometimes,  most  often  from  tuberculosis,  there  is  a  cavity  in  the  lung, 
and  this  may  be  of  any  size,  up  to  that  of  a  whole  lung.  Such  a  cavity 
gives  rise  to  cavernous  sounds  or  to  amphoric  breathing  when  of  moder- 
ate or  large  size,  the  breath  echoing  or  resounding  more  or  less  as  it 
enters  and  passes  by  the  openings  into  it.  If  the  cavity  be  of  small 
size,  the  first  third  or  so  of  inspiration  may  be  harsh  (as  the  air  forces 
a  way  into  it).  When  the  lung-tissue  is  solidified  it  serves  as  a  much 
better  conductor  of  the  bronchial  sounds  than  when  normal,  and  so 
the  latter  may  be  heard  in  an  abnormal  intensity  and  in  places  where  in 
health  they  are  faint;  on  the  other  hand,  the  vesicular  murmur  is  quite 
absent.  When  there  is  fluid  in  the  bronchioles  one  may  hear  the  crepi- 
tating sound  always  made  by  air  bubbling  through  a  small  quantity  of 
a  liquid.  This  is  the  condition  in  the  first  stage  of  pneumonia.  The 
same  condition  in  the  larger  bronchi  causes  mucous  rales.  When  the 
bronchioles  are  obstructed  (as  by  mucus)  in  just  the  right  degree,  an 
occasional  inspiration  only  penetrates  them  and  there  is  what  is  called 
cog-wheel  breathing  in  that  region  of  the  chest.  If  the  bronchioles 
are  mostly  filled  with  tough  mucus,  the  air  has  to  tear  its  way  through, 
causing  the  harsh,  rough  sounds  technically  known  as  rhonchi.  When 
this  condition  is  extreme  the  whole  adjacent  chest-wall  may  be  set  into 


128  RESPIRATION 

a  sort  of  vibration,  producing  the  effect  called  fremitus,  which  may  be 
felt  even  with  the  finger.  Rarely  there  are  in  a  cavity  both  air  and 
liquid,  and  we  hear  the  sound  arising  from  the  shaking  together  of  these 
two  sorts  of  fluids  in  a  vessel  (succussion). 

Anything  which  lessens  the  tone  or  elasticity  of  the  lung-tissue  pro- 
longs expiration,  this  process  being  one  of  passive  recoil.  Such  a  con- 
dition obtains  in  emphysema.  When  the  contiguous  surfaces  of  the 
pleura  (the  pulmonary  and  the  costal),  instead  of  being  very  smooth  and 
well  lubricated,  are  covered  more  or  less  with  exudated  solid  materials, 
there  is  friction  which  gives  rise  to  easily  heard  and  characteristic  sounds. 
This  happens  often  in  pleurisy  and  in  tuberculosis.  Sometimes,  as  in 
pneumothorax,  for  example,  the  conditions  in  the  lungs  are  such  that 
drops  of  liquid  fall  into  a  cavity.  Then  there  is  a  peculiar  sound  known 
often  as  metallic  tinkling.  It  may  be  produced  by  drops  of  secretion 
falling  from  the  end  of  a  bronchus  into  a  cavity. 

Some  Respiratory  Quantities. — The  capacity  of  the  lungs  and  the  rela- 
tions of  the  various  volumes  of  air  and  of  gases  remaining  and  passing 
in  and  out  under  various  circumstances  have  a  certain  interest  and 
importance  both  theroretically  and  therapeutically  as  well  as  for  the 
purposes  of  athletic  measurement.  The  first  of  these  that  we  need  to 
consider  is  the  tidal  air.  This  is  that  volume  of  air  which  goes  out  and 
in  at  every  breath.  On  the  average  in  the  adult  man  its  quantity  is 
about  500  c.c,  or  about  7  c.c.  per  kilo  of  body-weight.  Perhaps  the 
most  noteworthy  fact  about  the  tidal  air  is  its  small  amount  compared 
with  the  lung-capacity,  for  only  about  15  per  cent,  of  the  air  in  the 
lungs  under  normal  conditions  passes  out  at  each  breath.  This  fraction 
is  callefl  the  co-efficient  of  ventilation.  The  vital  capacity  of  any  indi- 
vidual is  the  volume  of  air  he  can,  by  the  greatest  effort,  expire  after 
the  most  complete  inspiration.  A  more  accurate  term  for  this  quantity 
would  be  respiratory  capacity,  its  importance  to  life  being  somewhat 
less  than  the  inventor  of  the  term  "vital  capacity"  supposed.  Vierordt 
states  that  for  man  on  the  average  it  is  3400  c.c,  and  for  woman  2500 
c.c,  a  marked  and  important  sexual  difference.  These  quantities, 
however,  may  be  raised  a  good  deal  by  practice  and  by  general  athletic 
training,  especially  by  running.  This  shows  probably  that  the  muscles 
of  the  bronchioles  may  be  developed  by  exercising  them,  so  that  more 
air  than  before  can  enter  the  alveoli. 

Other  respiratory  quantities  are  the  so-called  supplemental  air,  the 
complemental  air,  the  stationary  air,  the  residual  air,  the  bronchial 
capacity,  the  alveolar  capaeity,  and  the  lung-capacity.  What  these  are 
in  general  can  be  made  out  frrmi  their  names. 

The  Respiration  of  the  Fetus. — Unlike  the  circulatory  organs,  the 
fetal  mechanisni  of  respiration  does  not  begin  its  work  until  after  birth, 
when  for  the  first  time  it  can  have  air  with  which  to  inflate  the  lungs. 
The  fetus,  however,  breathes,  but  oxygen  and  not  air,  and  it  excretes 
the  carbon  dioxide,  inevitable  product  of  its  tissue-metabolism,  into  the 
maternal  blood  instead  of  into  the  atmosphere.    Fetal  respiration,  then, 


RESPIRATION  129 

is  wholly  internal  respiration.  The  respiratory  mode  of  mammalian 
embryos  is  practically  the  same  as  that  of  fishes,  for  althoiio'h  the  former 
have  no  proper  gills,  still  the  gases  interchange  (through  layers  of  maternal 
and  fetal  epithelium)  between  the  liquid  blood  of  the  embryo  and  the  liquid 
environment.  In  this  case  the  environment  is  the  circulation  in  the 
placenta  of  the  mother.  The  fecal  chorionic  villi  and  the  blood-filled 
sinuses  of  the  decidua  serotina  of  the  placenta,  extending  inward  from 
the  uterine  fundus,  interknit  with  the  greatest  closeness.  Thus,  the  villi 
of  the  fetal  circulation,  made  up  largely  of  capillaries,  are  quite  surrounded 
by  the  large  blood-sinuses  filled  with  maternal  blood.  The  circulation  of 
the  fetus,  then,  exchanges  its  two  respiratory  gases  through  the  walls  of 
capillaries  just  as  does  the  adult  circulation,  save  that  instead  of  exchang- 
ing them  with  the  alveoli  the  fetal  blood  takes  its  oxygen  and  excretes 
its  carbon  dioxide  second-hand,  as  it  were,  from  and  into  the  maternal 
circulation.  The  essence  of  these  facts  was  understood  by  Mayow  in 
England  as  early  as  1674. 

The  sinuses  of  the  maternal  circulation  in  the  placenta  are  large,  and 
the  blood-current  through  them  correspondingly  slow,  thus  allowing 
ample  time  for  the  respiratory  exchange.  Diffusion  would  partly  account 
for  the  interchange,  l)ut  probably  here  as  elsewhere  the  protoplasmic 
powers  of  the  septa  have  more  or  less  to  do  with  the  passage  through. 
Unlike  the  adult's  hemoglobin,  that  of  the  fetus  is  never  saturated  with 
oxygen.  An  estimate  of  the  oxygen  consumed  by  the  human  fetus  was 
0.169  gm.  daily  per  kilo  of  body-weight,  compared  with  the  14  gm.  or 
so  used  by  the  adult  per  kilo,  or  about  1.2  per  cent,  of  the  adult's 
requirement.  This  low  demand  for  oxygen  depends  on  a  correspond- 
ingly low  metabolism,  which  in  turn  is  due  to  the  relative  inactivity  of 
the  fetus,  its  protection  from  loss  of  heat,  etc. 

Respiration  through  the  Skin. — The  lungs  are  not  the  only  organs 
by  which  oxygen  is  absorbed  into  the  organism  and  carbon  dioxide 
given  off,  for  the  skin  and  the  intestines  are  also  media  for  a  small  amount 
of  this  interchange,  even  in  mammals.  This  is  not  difficult  to  understand, 
for  a  part  of  the  tissues  of  the  body,  constantly  producing  carbon  dioxide 
and  rec[uiring  oxygen,  are  separated  from  the  atmosphere,  the  great 
reservoir  of  both  these  gases,  only  by  the  thin  upper  layers  of  the  skin. 
This  important  organ,  the  skin,  is  in  some  respects  an  admirable  osmotic 
membrane,  being  moist,  thin,  and  vascular.  The  structure  of  its  outer 
layer,  the  epidermis,  however,  is  not  so  favorable  to  respiration,  the 
epidermis  being,  indeed,  evolved  to  be  negative  and  protective. 

Cruikshank  more  than  a  century  ago  proved  that  a  clean  hand  or  foot 
immersed  in  lime-water  (a  solution  of  calcium  oxide)  for  an  hour  ren- 
dered the  water  milky  by  the  production  of  the  insolul)le  calcium  car- 
bonate— the  ordinary  test  for  carbon  dioxide.  Abernethy  thereupon 
showed  that  in  ordinary  air  oxygen  was  absorbed  and  carbon  dioxide 
discharged  by  a  hand  as  readily  as  in  pure  oxygen.  Gerlach,  from 
experiments  on  a  part  of  a  man's  skin,  calculated  that  8.4  gm.  of  carbon 
dioxide  were  given  off  in  twenty-foin-  hours  from  the  entire  bodily  sur- 
9 


130  •  RESPIRATION 

m 

face.  Scharling,  Rohrig,  and  others  proved  that  carbon  dioxide  was 
given  off  from  all  parts  of  the  body,  but  at  verv  various  rates  in  different 
portions.  Anything  which  increases  the  vascularity  of  the  skin  increases 
also  the  respiration  through  it.  As  in  case  of  the  pulmonary  interchange, 
heightened  metabolism  causes  a  livelier  respiration  through  the  skin; 
so,  according  to  Fubini  and  Rouchi,  do  food  and  light.  In  general, 
cutaneous  respiration  seems  to  be  about  -^^q  (0.5  per  cent.)  of  the  pul- 
monary respiration  in  quantity.  Trial  demonstrates  that  the  human 
skin  will  absorb,  besides  oxygen  and  carbon  dioxide,  carbon  monoxide, 
sulphuretted  hydrogen,  and  the  vapors  of  chloroform  and  of  ether. 

In  amphibians,  dermal  respiration,  especially  the  absorption  of  oxygen, 
is  a  much  more  important  process  than  in  mammals.  Frogs,  for  example, 
during  a  third  or  more  of  the  year  in  temperate  climates,  are  buried  in 
the  mud  at  the  bottom  of  ponds  and  streams,  and  the  use  of  their  lungs 
must,  then,  for  mechanical  reasons  be  only  nominal.  But  metabolism 
goes  on  during  these  months  and  requires  oxygen  as  it  does  in  the  summer 
time.  The  carbon  dioxide  produced  must  be  given  off  too,  or  the  ani- 
mal would  soon  die  of  asphyxia.  Klug  found  that  the  body-surface  of 
the  frog  exclusive  of  the  head  excreted  three  or  four  times  as  much  carbon 
dioxide  as  did  the  lungs  and  the  skin  of  the  head — namely,  about  0.2  gm. 
in  the  three  hours  of  the  experiment.  In  the  summer  the  opposite  ratio 
obtains,  the  lungs  then  being  the  more  important.  Dissard,  however, 
proved  that  the  frog  dies  when  either  of  these  respiratory  organs  (the 
skin  or  the  lungs)  are  thrown  out  of  function.  There  is  need,  then,  of 
experiment  in  this  direction  on  various  classes  of  hibernating  animals  as 
well  as  on  the  fakirs  of  India,  who  seem  to  be  piactically  hibernating 
men,  their  hearts  and  lungs  being  nearly  at  a  standstill. 

Respiration  through  the  Wall  of  the  Alimentary  Canal. — Just  as  gases 
pass  outwarfl  through  the  skin  from  the  underlying  tissues,  so  a  similar 
and  more  variefl  respiratory  interchange  takes  place  into  and  out  of  the 
alimentary  canal.  Ruge  found  carbon  dioxide,  hydrogen,  nitrogen, 
methane,  and  hydrogen  sulphide  in  the  rectum  of  a  man,  but  no  oxygen. 
The  carbon  dioxide,  methane,  and  hydrogen  sulphide  were  most  abun- 
dant on  a  vegetable  diet,  the  nitrogen  on  an  animal  diet,  and  the  hydro- 
gen on  a  milk  diet.  The  proportion  of  carbon  dioxide  in  the  intestines 
varies  from  20  to  90  per  cent,  of  the  total  gas  content  (Tappeiner).  Its 
partial  pressure  would  be  greater  than  that  of  the  tissues,  whether  solid 
or  liquid,  about  the  gut.  The  carl)on  dioxide  of  the  intestines,  therefore, 
woulfj  soon  make  its  way  into  the  circulation  and  be  excreted  l^y  way  of 
the  lungs. 

Oxygen  is  promptly  absorbed  from  the  alimentary  canal  l)y  the  sur- 
rounding tissues  and  largely  by  the  capillary  blood.  It  can  seldom 
he  found  below  the  dufKlcnuin,  for  most  of  it  is  absorbed  by  the  wall  of 
the  stomach.  Peinbrey  relates  that  swimmers  who  are  in  the  habit  of 
staying  under  water  an  exceptionally  long  time  swallow  air  into  their 
stomachs,  in  order  that  the  oxygen  so  taken  in  may  be  utilized  as  well 
as  that  of  the  lungs.    A  kitten  with  clamped  trachea  will  die  in  thirteen 


RESPIRATION  131 

minutes,  but  if  a  current  of  air  be  passed  through  the  intestine  after 
closure  of  the  trachea  it  will  live  61  per  cent,  longer.  In  fish,  intestinal 
respiration  is  probably  as  important  as  dermal  respiration  is  to  amphi- 
bians. 

In  the  frog,  at  least,  the  mucous  membrane  of  the  mouth  and  pharynx 
is  an  important  respiratory  organ,  and  in  a  species  of  salamander  more 
respiratory  exchange  takes  place  in  these  localities  than  is  conducted  by 
the  skin  on  the  whole  surface  of  the  body. 

The  Quantity  and  Quality  of  Air  Required  for  Respiration. — In  order  that 
respiration  may  l^e  conducted  normally  and  with  an  expenditure  of  only 
a  minimum  amount  of  energy,  it  is  necessary  that  the  air  to  be  breathed 
should  be  pure  within  certain  physiological  limits — that  is,  that  it  should 
contain  enough  oxygen  and  not  too  much  carbon  dioxide.  The  atmos- 
sphere  being  for  all  respiratory  purposes  a  boundless  reservoir  of  oxygen 
and  an  infinite  absorber  of  carbon  dioxide,  the  most  natural  way  of 
maintaining  the  requirements  inside  our  dwellings  and  assembly  rooms 
is  to  let  in  fresh  air  in  the  required  amount.  As  it  enters  this  necessarily 
drives  out  an  ecjual  amount  of  air  already  present,  but  more  or  less  viti- 
ated. This  is  the  simple-enough  principle  of  ventilation.  The  problems 
then  are  to  determine  how  much  air  per  hour  a  person  needs  for  perfect 
breathing,  anfl  then  to  so  provide  this  quantity  of  air  from  the  atmos- 
phere under  all  its  varying  conditions  that  the  supply,  without  draughts 
of  a  harmful  intensity,  may  be  certain,  economical,  and  constant.  The 
former  part  of  this  problem  has  been  solved  satisfactorily;  the  latter  part 
in  everyday  life  is  not  so  easy. 

The  ratio  of  required  oxygen  to  carbon  dioxide  cast  out  is  so  fairly 
constant  that  it  is  customary  to  measure  the  purity  of  a  given  mass  of  air 
to  be  breathed  by  the  percentage  of  carbon  dioxide  it  contains.  Each 
adult  man  or  woman  is  found  to  expire  about  0.6  cubic  foot  of  carbon 
dioxide  on  the  average  every  hour.  In  a  room  of  ten  feet  cube  this 
w^ould  make  the  proportion  of  carbon  dioxide  at  the  end  of  the  hour 
0.06  per  cent.,  and  this  proportion  is  taken  as  the  proper  maximum  of 
vitiation  by  this  gas.  It  is  an  index  also  of  the  oxygen  required.  In 
ordinary  dwellings,  on  average  days,  if  there  be  but  one  person  to  this 
space — namely,  to  every  thousand  cubic  feet — ventilation  wall  take  care 
of  itself  through  the  cracks  about  the  windows  and  the  doors,  draughts 
in  the  chimneys,  and  by  the  opening  and  closing  of  the  doors.  When, 
however,  more  than  one  person  breathes  from  this  thousand  cubic  feet 
of  air  the  problem  is  complicated,  and  chiefly  by  the  fact  that  in 
winter  a  draught  of  air  at  once  cools  off  a  room  and  imposes  on  the 
occupants,  at  least  indirectly,  some  slight  risk  of  a  catarrhal  inflam- 
mation of  the  nose  or  chest,  of  neuralgia,  etc. — in  short  of  "taking 
cold." 

The  ideal  mode  of  ventilation  undoubtedly  is  by  means  of  an  open- 
grate  fire  in  every  room,  and  modern  dwellings  of  the  better  class  are  fast 
meeting  this  ideal.  Even  if  no  fire  be  Inirning  in  the  grate,  there  is  a 
draught  of  considerable  proportions  constantly  passing  up  the  chimney. 


132  RESPIRATION 

This  draws  an  equivalent  volume  of  air,  moist  and  cool,  through  the 
cracks  about  the  doors  and  windows,  if  not  from  a  supply  provided  by 
some  system  of  ventilating  apparatus. 

Perhaps  the  next  best  form  of  heating,  so  far  as  ventilation  is  concerned, 
is  the  hot-air  furnace.  When  properly  built  and  run,  it  provides  a  cur- 
rent of  fresh  air  from  out  of  doors  warmed  and  humid  enough  to  be 
breathed.  Steam  and  hot  water  have  so  great  mechanical  advantages 
that  their  use  is  becoming  very  widespread.  Neither  of  these  methods, 
however,  provides  any  ventilation  nor  any  mode  of  moistening  the  air. 
The  heating-stove  has  these  disadvantages  in  an  exaggerated  form  because 
of  the  extreme  temperatures  they  often  reach,  while  the  small  basin  of 
water  sometimes  attached  to  the  stove  above,  intended  to  moisten  the 
air,  is  almost  ludicrously  inadequate.  Whatever  the  mode  of  heating, 
the  matter  of  direct  ventilation  by  means  of  open  windows  will  seem  to 
the  next  generation  a  very  simple  matter,  and  children  now  being  born 
will  look  back,  we  may  imagine,  with  mild  amazement  on  the  fear  many 
of  their  parents  and  grandparents  now  have  of  a  current  of  air.  Edu- 
cation is  advancing  rapidly  in  this  important  regard,  and  it  is  a  common 
experience  that  toleration  even  of  cold  draughts  may  be  readily  acquired 
without  any  sort  of  harm  and  with  great  benefit  to  everyone;  and  with 
life  itself  to  the  millions  of  every  century  who  else  would  die  of  tuber- 
culosis of  the  lungs. 

Diffusion  also  assists  ventilation  everywhere  to  no  small  extent,  quickly 
evening  up  the  composition  of  the  air  in  an  open  space.  Difference  in  tem- 
perature and  consequent  density  of  air  is  another  cause  of  the  air's 
movement.  A  fair  allowance  of  air  space  in  the  large  cities  is  1500  cubic 
feet,  and  4500  cubic  feet  of  air  hourly  per  capita.  The  floor-space  should 
be  one-tenth  of  the  cubic  space. 

A  method  of  puVjlic  school-room  ventilation  especially  that  commends 
itself  on  many  accounts  is  the  free  opening  of  the  windows  for  live 
minutes  every  half-hour,  the  pupils  meanwhile  marching  about  the 
room.  This  would  keep  the  air  pure  at  a  low  monetary  cost.  It  would 
relieve  the  brain  of  its  congestion  by  vaso-motor  rearrangement  of  the 
blood,  and  it  would  accustom  the  child  to  small  changes  in  the  temper- 
ature of  the  air.  Under  such  a  system,  harmful  over-strain  of  the  mind, 
eyes,  etc.,  would  be  much  rarer  than  now,  and  the  supply  of  respiratory 
oxygen  greatly  increased. 

Save  in  the  hospitals,  the  problem  of  ventilation  certainly  will  be  a 
simpler  one  continually  as  more  and  more  of  the  mass  of  the  people 
hear  and  believe  the  gospel  of  fresh  air  as  taught  them  in  the  schools — 
that  oxygen  is  as  fowl  and  drink  and,  unlike  them,  free;  and  to  take  it 
in  great  abundance  day  and  night  is  to  ward  off  multiform  disease  and 
to  add  to  the  length  and  happiness  of  their  lives. 


CHAPTER    IV. 

FOODS. 

In  studying  respiration  we  saw  in  some  of  its  bearings  the  status  of 
oxygen  as  one  of  the  indispensable  supphes  of  the  organism.  The  dis- 
cussion demonstrated  that  hving  protoplasm  requires  oxygen  ior  its 
metabohsm,  and  it  ."howed  furthermore  how  the  protoplasm  which  makes 
up  the  human  body  gets  its  oxygen,  and  what  finally  becomes  of  it.  In 
the  present  chapter  we  begin  the  description  of  the  same  sort  of  acquiring 
and  disposing  process  for  the  remainder  of  the  material  provisions  on 
which  the  body  subsists  and  in  the  metabolism  of  which  it  lives.  Oxygen 
is  a  sort  of  food,  but  as  it  is  a  gas  it  requires  special  means  for  receiving 
it  and  for  excreting  the  products  of  its  use.  All  food  other  than  oxygen 
is  either  solid  or  licjuid  in  its  density,  and  because  of  this  difference  has 
required  the  evolution  and  action  of  a  mechanism  peculiar  to  itself. 

In  describing  the  natural  history  of  food  proper  and  its  organic  use 
we  need  to  understand  the  nature  of  the  various  classes  of  alimentary 
substances  and  their  general  relations  to  the  organism. 


THE  GENERAL  NATURE  OF  A  FOOD. 

A  food  or  nutrient  may  be  defined  as  anything  which,  taken  into  an 
organism,  is  capable  of  supplying  it  with  tissue  or  of  producing  energy. 
Let  us  as  a  preliminary  to  our  study  of  the  nutrients  see  of  what  materials 
an  average  animal  body  is  made  up,  in  order  that  we  may  know  in 
advance  what  substances  will  be  required  in  the  food  for  supplying  tissue, 
whether  in  the  growing  young  animal,  or  in  the  replacement  of  the  nor- 
mal loss  by  wear  and  tear.  We  have  already  learned  what  chemical 
elements  combine  to  make  up  an  animal  organism. 

The  Animal  Organism's  Proximate  Principles. — The  table  on  page  30 
is  given  partly  as  a  place  for  reference  to  the  names  and  classification 
of  the  chief  constituent  compounds  so  far  known  to  exist  in  an  average 
animal  body  of  high  development,  and  partly  to  suggest  the  need  of  very 
various  materials  in  the  food  which  is  to  reproduce  all  these  substances 
as  they  bit  by  bit  wear  away.  The  iron,  manganese,  ammonia,  and 
carbon  dioxide  mentioned,  and  probably  the  nitrogen  and  hydrogen,  exist 
only  to  a  minute  extent  in  free  uncombined  form  in  the  body.  The  others, 
and  doubtless  many  more  proteid  forms,  and  especially  enzymes  and 
salts  of  the  alkaline  metals,  seem  to  be  present  as  such  in  large  or  small 
quantities.     The  proportion  of  water  given,  65  per  cent.,  is  constantly 


134 


FOODS 


changing,  but  is  approximately  correct  as  an  average.  The  relatively 
large  proportion  of  water,  approximately  two-thirds  of  the  body,  again 
reminds  us  of  the  fact,  important  in  understanding  the  movements  of  the 


'°>'>'^.. 


AMMONIA 
COMPOUNDS 


»''■*■  BOO 


'^^^^o.l^^l^^f 


The  nitrogen  food-cycle.      (Hutchison.) 


tissues,  that  the  body,  apparently  solid,  is  made  up  largely  of  liquid  proto- 
plasm— in  the  ancient  medical  dictum,  corpora  non  agunt  nisifiuida. 


Fig.  71 


EXPIRED 


ATMOSPV^* 
The  carbon  food-cycle.      (Hutchison.) 

Through  the  agency  of  light,  plants  have  the  ])o\ver  of  c()m})ining  the 
water  of  the  soil  and  the  carbon  dioxide  of  the  air  into  sugar.  Further- 
more, plants  make  from  this  sugar  starch  and  cellulose  and  fats,  and 


THE  GENERAL  XATURE  OF  A   FOOD 


135 


Fig.  72 


combine  it  with  iiitrogeii-hearinf^  radicles  of  the  s(^il  to  form  proteids. 
It  is  then  the  chlorophyll,  very  like  hemoglobin,  which  synthesizes  certain 
inorganic  elements  into  more  complex  substances,  protein,  fats,  and 
carbohydrates.  These  three  with  water  and  inorganic  salts  make  up  the 
necessary  fo(Ml  of  all  animals.  These  proteids,  fats,  and  carljohydrates, 
stored  with  the  potential  energy  coming  from  the  sun,  expended  in  mak- 
ing them,  animals  again  analyze  into  simpler  compounds,  and  these  are 
essentially  those  with  which  the  plants  again  begin  their  work.  The 
stored  energy  thus  liberated  is  the  originator  of  the  movements  which, 
life,  especially  animal  life,  essentially  is.    The  formula 

(GCO2  +  5H2O)  n  =  (CfiHioOa)   +  O  n 

is,  therefore,  typical  for  the  synthesizing  function  of  plants,  and  its 
reversal — 

(CsH^A)  n   +  O  n  =   (6C0,   +  .5H,0)  n 

is  characteristic  of  the  analyzing,  energy-liberating  function  of  animals. 
Plants  and  animals  in  this  way  are  mutually  dependent,  and  thus  runs 
the  eternal  round  of  matter.  It  is  the  es- 
sence of  vegetable  life,  so  far  as  we  are  at 
present  concerned  with  it,  to  synthesize 
the  molecule  of  starch,  but  it  does  this 
only  through  the  obscure  agency  of  the 
chlorophyll  of  its  verdure.  This  sub- 
stance, it  is  interesting  to  note,  is  largely 
a  proteid,  the  baffling  nature  of  whose 
life-mystery  has  already  l)een  pointed  out. 
Nutrient  Proximate  Principles.  —  The 
table  of  chemical  compounds  (page  30), 
already  isolated  from  a  highly  evolved 
animal  body,  is  made  up  chiefly  of  six 
classes  of  substances:  protein,  fats,  carbo- 
hydrates, albuminoids,  inorganic  salts, 
and  w^ater.  Each  one  of  these  classes  is 
probably  represented,  at  least  in  minute 
amount,  in  any  particle  of  living  matter, 
for  analysis  of  masses  of  the  purest  proto- 
plasm obtainal)le  always  shows  the  pres- 
ence of  at  least  the  first  three  of  these 
and  water.  Logically,  then,  these  deter- 
mine w^hat  foods  animals  require  as  sup- 
plyers  of  tissue,  and  we  find,  in  fact,  that 
all  actual  nutrients  used  by  man  the  world  over  may  be  divided  into  the 
six  classes — proteids,  albuminoids,  fats,  carbohydrates,,  inorganic  salts, 
and  water.  If  we  are  guided  by  empirical  conditions  of  actual  diets, 
w^e  must  add  to  these  two  other  classes,  stimidants  and  condiments,  the 
latter  of  essential  importance. 


A  fibula  tieil  in  a  knot,  after  mac- 
eration in  acid  to  remove  it,*  lime,  etc. 
(From  a  specimen  in  the  College  of 
Physicians  and  Surgeon*,  New  York.) 
(Dalton.) 


136  FOODS 

General  Requirements  in  a  Food. — The  total  food  of  an  animal  at 
(Jili'erent  periotls  of  his  life  must  meet  three  requirements  (as,  indeed, 
Aristotle  long  ago  pointed  out),  each  indispensable:  (1)  Throughout 
life  the  food  must  be  able  to  supply  energy,  by  expending  which  the 
animal  lives.  Previous  to  its  birth  this  energy,  like  the  body-tissues, 
was  derived  ready-made  from  the  maternal  organism,  (2)  Until 
maturity  the  food  must  afford  the  materials  for  constant  bodily  growth — 
that  is,  the  tissues  must  be  built  up  faster  than  they  are  worn  away  by 
use.  (3)  At  all  periods  of  life  the  food  must  furnish  a  continuation  of 
the  tissue-material  used  up  and  worn  out  by  the  universal  wear  and 
tear  to  which  all  material  objects  are  subject  in  some  degree  or  other. 

All  food  taken  into  the  body  and  digested  is  reduced  to  the  simplest 
terms  in  which  it  can  retain  its  characteristics.  These  food-elements  are 
then  reconstructed  by  the  eating  animal  into  his  own  sort  of  tissues  or 
proximate  principles.  In  other  words,  there  is  never  any  direct  trans- 
ference of  food -materials  from  the  flesh  of  one  animal  to  that  of  another. 
When  a  man  eats  pork,  his  tissues  do  not  become  more  like  those  of  a 
pig;  and  sheep-fat  is  never  to  be  found  in  a  dog's  adipose  tissue  after 
being  fed  even  wholly  on  mutton  (except  under  the  abnormal  conditions 
of  forced  feeding  far  beyond  the  limits  of  normal  digestion).  Just  as  in 
a  paper-mill  all  sorts  of  paper  and  rags  are  macerated  together  and  then 
run  out  as  one  fresh  homogeneous  product,  so  in  organisms  protein,  fat, 
carbohydrate,  albuminoid,  inorganic  salts,  and  water  are  run  through  the 
mechanism  of  the  individual's  digestion  and  absorption  and  are  assimi- 
lated to  the  special  likenesses  of  the  particular  tissues  of  which  perhaps 
they  are  to  form  a  part.  Chemically  as  well  as  histologically  the  muscle  of 
no  two  sorts  of  animals  is  exactly  alike,  yet  every  one  of  them  may  serve 
in  part  as  the  chief  and  adequate  food  of  any  other  carnivorous  animal.  If 
the  flesh  of  seagulls  tastes  like  that  of  fish  it  is  because  these  birds  at  times 
gorge  themselves  with  fish  far  beyond  even  their  powers  of  assimilation, 
although  not  beyond  their  digestive  powers.  Only  recently  has  it  been 
learned  how  complete  is  the  tearing-down  of  food  in  the  alimentary 
canal.  The  absorbing  wall  of  the  intestines  has,  therefore,  powers  of 
recombining  these  food -elements,  "proximate  principles,"  to  a  degree 
much  greater  than  was  a  few  years  ago  suspected. 

By  the  definition  in  common  use,  any  substance  which  produces  in 
an  organism  animal  tissue  and  energy  or  either  of  these  is  a  food.  Neither 
of  these  results,  however,  can  be  eft'ected  until  the  nutrient  has  been  actu- 
ally ab.sorV)ed,  after  its  digestion,  at  least  into  the  circulating  fluid  of  the 
bwJy,  the  blow! ,  and  has  thus  become  a  part  of  the  organism.  Thus,  a 
food  is  really  a  food  only  after  it  has  been  absorbed.  Two  requisites  of 
a  food,  then,  are  digestibility  and  absorbability.  The  prerequisite  of 
digestibility  is  obviously  essential.  No  substance,  candidate  for  use  as 
a  foo<l,  unless  directly  soluble  in  water  or  the  normal  alkaline  salines  of 
the  body  (saliva,  the  i)lood  and  lymph,  etc.),  can  be  digested  except  those 
proximate  principles  of  nutrients  so  often  rehearsed — namely,  proteids, 
fats,  carbohydrates,  and  albuminoids.     These  predominant  components 


THE  GENERAL  NATURE  OF  DIET  137 

of  various  focxls  vary  widely,  however,  in  the  degree  of  their  respective 
absorbabihty  which  is  so  essential.  Atwater  calculated  from  a  large 
amount  of  data  that  from  a  mixed  diet  the  following  proportions  of 
nutrient  components  are  on  the  average  absorbed  : 

Percentages  of  Absorption. 


Nutrients. 

Proteid. 

Fat. 

Carbohydrates. 

Animal  foods 
Cereals  and  sugars    . 
Vegetables  and  fruits 

98% 
85% 
80% 

97% 
90% 
90% 

100% 
98% 
95% 

Another  characteristic  of  foods  is  that  they  should  require  digestion. 
This  is  on  the  universal  principle  that  lack  of  exercise  allows  an  organ 
to  degenerate.  If  the  muscular  and  chemical  arrangements  of  the 
intestine  are  not  employed  actively  they  tend  to  lose  their  vigor.  This 
is  the  objection  to  the  large  use  of  partly  predigested  foods. 


THE  GENERAL  NATURE  OF  DIET. 

A  diet  is  a  selection  of  nutrients  so  arranged  as  to  meet  continuously 
the  requirements  of  an  organism.  This  selection  may  be  almost  uncon- 
scious, as  was  formerly  that,  for  example,  of  an  average  farmer's  family. 
It  may  be,  on  the  other  hand,  the  exactly  defined  choice  like  that  of  the 
army,  or  of  a  modern  scientific  research,  like  that,  for  instance,  con- 
ducted by  the  Department  of  Agriculture  on  the  harmfulness  of  com- 
mercial food-preservatives.  The  selection  may  be,  in  case  of  the 
wealthy,  from  the  whole  artistic  menu  of  the  chef  of  a  great  hotel,  or, 
at  the  other  logical  extreme,  in  reality  no  choice  at  all,  on  which 
basis  was  once  the  diet  of  potatoes  of  the  Irish  peasant  and  the  rice  of 
the  Chinese.  Still,  the  leading  notions  in  the  term  "diet"  are  those  of 
a  set  arrangement  of  nutrients  for  a  considerable  space  of  time,  suffi- 
cient, at  least,  to  allow  of  observation  of  its  effect,  good  or  bad,  general 
or  special,  on  an  organism. 

Of  the  general  requirements  of  a  normal  or  ideal  diet,  so  understood, 
there  are  at  least  six  which  should  be  noted:  (1)  A  diet  must  contain 
both  energizers  and  tissue-builders;  (2)  it  must  be  sufficient  in  quantity 
to  support  the  organism  in  normal  condition,  but  no  larger  in  amount; 
(3)  it  must  have  the  alimentary  proximate  principles  or  components  in 
nearly  the  proportions  which  best  suit  the  needs  of  the  organism;  (4)  it 
must  contain  a  variety  of  nutrients  both  for  each  meal  and  from  day  to 
day;  (5)  it  must  be  adapted  more  or  less  accurately  in  a  quantitative 
way  to  the  particular  use  of  the  organism  under  its  specific  conditions  at 
the  time;  (6)  it  must  be  adapted  also  qualitatively  to  the  organism's 
needs  in  certain  physiological   (and  pathological)  periods. 

A  Source  Both  of  Energy  and  of  Tissue. — Of  the  six  alimentary  com- 
ponents   already   frequently    mentioned    (proteids,    albuminoids, "  fats. 


138  FOODS 

carbohydrates,  inorganic  salts,  and  water),  five,  all  except  water,  are 
sources  of  eucnjy  by  their  metabolism,  chiefly  katabolism,  in  the  body. 
It  is  possil^le  that  the  ingested  water  also  may  be  in  part  decomposed, 
or,  more  probably,  may  unite  with  the  simple  products  of  katabolism  in 
anabolic  processes,  thus  producing  energy;  of  this  little  is  definitely 
known.  Of  the  familiar  six,  three  only  are  sources  of  tissue  considered 
as  active  bioplasm  (that  is,  excluding  fat) — namely,  proteids,  inorganic 
salts,  and  water.  Carbohydrates  and  fats  are  sources  of  tissue-fat,  but 
the  latter  is  relatively,  at  least,  unimportant  in  the  actual  life  of  the 
animal  in  health,  and  in  this  relation  is  not  considered  as  tissue- 
protoplasm.     It  is  a  tissue,  but  one  of  a  special  sort. 

The  Grand  Division  of  Nutrients. 

Sources  of  bioplasm.  Sources  of  energy. 

Proteids.  Proteids. 

Inorganic  salts.  Inorganic  salts. 

Water  Fats. 

Carbohydrates. 

Albuminoids. 

Water  (?). 

Of  the  three  sources  of  protoplasm,  proteids  alone  are  by  themselves 
producers  of  protoplasm,  for,  of  course,  feeding  inorganic  salts  or  water, 
or  both  together,  and  nothing  else,  could  do  nothing  toward  continuously 
supporting  life.  Actual  starvation  is,  however,  excepted,  for  then  water 
will  prolong  vitality;  in  case  of  the  higher  animals  entire  lack  of  water 
kills  much  more  quickly  than  entire  lack  of  other  nutrients.  (Lack  of 
all  sleep  destroys  life  sooner  than  lack  of  either  food  or  drink.) 

This  division  of  the  proximate  principle  of  foods  into  two  classes,  one 
of  which  supplies  to  the  animal  both  active  tissue  and  energy,  and  the 
other  of  which  furnishes  only  energy,  is  of  the  largest  importance  in 
the  phvsiology  of  nutrition.  Notwithstanding,  the  division  is  far  from 
absolute,  in  that  even  a  carnivorous  animal  requires  for  continued 
existence  at  least  a  very  small  proportion  of  fats  and  carbohydrates  as 
well  as  the  proteids,  the  mineral  salts,  and  water  mentioned  in  the 
table.  The  reason  for  this  is,  as  has  already  been  stated,  the  com- 
position of  the  living  substance.  As  will  be  recalled,  it  seems  always 
to  contain  some  fat  and  especially  some  carbohydrate.  The  char- 
acteristically vital  particle  probably  consists  of  all  of  these  molecules 
in  some  sort  of  combination  or  other — proteid,  carbohydrate,  fat,  salts, 
and  water  in  one  unstable  vital  mass.  However,  in  general  terms,  an 
animal  can  live  on  proteids,  inorganic  salts,  and  water,  but  not  on  fats, 
carbohydrates,  salts,  and  watei',  singly  or  in  any  combination.  This 
gives  proteid  a  preeminence  as  an  alimentary  component,  a  preeminence 
which  men  in  general  as  well  as  physiologists  appreciate.  The  immedi- 
ate reason  for  this  superiority,  of  course,  is  obvious:  the  proteids  alone 
(save  as  noted  below)  contain  nrfrnc/en,  available  for  the  building  of 
new  alVjumin  in  the  ever-wasting  animal  tissues.     In  the  nitrogen  most 


THE  GENERAL  NATURE  OF  DIET  139 

probably,  as  was  seen  in  our  first  chapter,  perhaps  in  the  cyanogen- 
combination,  hes  the  vital  nexus.  Why  animal  organisms  cannot  take 
this  nitrogen  from  allmminoids  or  from  salts  containing  nitrogen,  science 
at  present  cannot  tell  us.  The  hemoglobin-like  l)io})lasm  of  the  vegetal 
kingdom  seems  to  do  this  paramount  work  for  all  living  organisms. 

The  five  food-components  which  are  surely  sources  of  energy  in  the 
body  (proteids,  albuminoids,  fats,  carbohydrates,  and  mineral  salts,  with 
the  possible  addition  of  wafer)  produce  this  energy  in  a  multiplicity  of 
ways  of  chemical  reaction.  These  methods  are  mostly  katabolic  in  trend, 
but  some  are  partly  anabolic.  Some,  too,  of  the  reactions  doubtless  occur 
in  other  ways  which  could  be  classed  technically  as  neither  anabolic  nor 
katabolic,  since  the  large  majority  of  chemical  processes  are  productive  of 
some  degree  of  heat.  In  the  case  of  fats  and  carbohydrates  the  general 
reaction  is  doubtless  oxidation,  a  good  part  of  the  energy  produced  chemi- 
cally in  animals  being  derived  from  this  source.  The  katabolism  of 
proteids  and  of  albuminoids  is  more  complex  than  that  of  fats  and  car- 
bohydrates, but  especially  in  case  of  the  tissue-proteids  (as  distinguished 
from  the  circulating  proteids,  mostly  serum  albumin  and  serum  globulin), 
is  partly  a  process  of  oxidation  also.  One  must  not  lose  sight  of  the  simple 
parallelism  between  an  organism  and  a  steam-engine  in  that  in  both  cases 
the  actual  burning  of  fuel,  largely  carbonaceous,  is  necessary  for  the 
production  of  energy.  This  is  expended  partly  as  work,  "  the  overcoming 
of  resistance,"  and  partly  as  heat,  which  latter  is  quite  essential  in  the 
organism,  but  not  in  the  steam-engine.  There  are,  besides  these,  other 
modes  of  vital  energy-expense,  mentioned  in  the  chapter  on  Nutrition.  V/e 
shall  soon  see  (vuider  Calorimetry,  p.  140)  how  accurately  the  total  energy 
set  free  in  an  organism  can  now  be  measured,  and  how  fidly  the  com- 
bustion-values, although  not  too  strictly  the  organic  energy-production, 
of  any  nutrient  can  be  estimated  and  allowed  for  in  the  study  of  diets. 

Most  foods  in  actual  use  contain  both  energizers  and  tissue-producers, 
but  some  important  foods  do  not.  No  animal,  no  man,  for  instance, 
could  live  on  pure  sugar,  butter,  or  starch,  for  these  contain  nothing 
which  could  replace  the  wasting  protein  muscles  whereby  his  body  and 
its  organs  are  moved.  Man  could  not  live  on  gelatin,  for  although  it  con- 
tains the  needful  nitrogen,  the  latter  is  for  some  reason  locked  up  in 
unavailable  combination.  On  simple  bread,  potateos,  rice,  corn, 
oatmeal,  or  flesh  (water  being  added  in  each  case)  a  person  could,  if 
necessary,  live  a  long  time,  for  each  of  these  contains  proteids,  carbo- 
hydrates, fat,  and  inorganic  salts,  although  in  very  various  proportions. 
On  eggs  alone  or  on  milk  alone  life  endures  in  theory  for  an  unlimited 
time,  for  these  are,  of  course,  the  sole  diet  of  young  birds  before  hatching 
and  of  all  young  mammals.  In  practice,  however,  it  is  doubtful  if  a 
normal  human  adult  could  stand  the  strain  of  livino;  solelv  on  either  of 
these  for  many  years — surely  not  in  a  well-nourished  condition.  Our 
first  requirement  of  an  adequate  diet  is  that  it  contains  both  tissue- 
builders  and  sources  of  vital  energy,  but  considerations  other  than  this 
are  essential. 


140  FOODS 

The  Right  Quantity  is  Important. ^ — Our  second  ideal  requirement  is  that 
the  quantity  of  the  food  sliould  be  sufhcient  for  the  normal  needs  of  the 
organism,  but  not  excessive.  This  is  well-nigh  axiomatic,  and  yet  its 
scientific  meaning  demands  expression  and  the  average  limits  of  a  normal 
diet,  maximal  and  minimal,  require  some  discussion.  If  a  diet  be  too 
small  in  amount,  short  of  fasting  or  its  continuance  into  starvation,  the 
consequences  are  a  diminution  both  of  tissue-repair  and  of  the  energy 
of  the  botly.  The  organism  which  is  living  or  has  lived  on  its  own  tissue- 
fat  to  help  meet  the  deficiency  of  income  shows  that  bony  angularity 
most  of  us  are  famihar  with,  unfortunately,  sooner  or  later,  in  all  localities. 
The  individual  is  obviously  weak,  and  exertion,  either  physical  or  mental, 
requires  an  unusual  effort.  The  deficiency  in  heat-production  is  felt  in 
cold  weather  in  that  sense  of  continual  chill  to  which  very  poor  folk 
strive  in  vain  to  become  used,  the  thermometer  showing  perhaps  half 
a  degree's  depression  of  the  body-temperature. 

The  determination  of  the  quantity  of  food  in  an  average  diet  has  been 
and  is  a  matter  of  much  research  and  of  more  discussion.  The  explana- 
tion of  this  indeterminateness  is  to  be  found  in  the  very  widely  differing 
needs  and  habits  of  the  classes  and  divisions  of  mankind.  Physiology  has 
been  heretofore  very  largely  a  descriptive  science,  analyzing  and  system- 
atizing what  it  finds  in  Nature,  and  only  gradually  is  it  becoming  a  nor- 
mative science  which  sets  ideals  or  tells  what  ought  to  be.  In  this  case, 
therefore,  we  can  but  describe  what  people  actually  do  eat,  and  if  the 
science  declares  what  men  should  eat,  how  their  diets  ought  to  be  com- 
posed, it  will  be  only  by  taking  as  a  basis  the  best  average  of  actual 
diets  used  by  any  class  of  persons  that  can  be  arrived  at.  It  is  only  the 
faddists  and  the  "cranks"  who,  on  any  other  basis  than  this  which  is 
natural  and  actual,  say  what  men  should  eat.  Still,  of  late,  quantitative 
researches  have  been  made  by  methods  soon  to  be  described,  which,  in- 
<lependently  of  actual  dietary  conditions,  have  more  or  less  well  estab- 
lished the  proper  amount  of  food  for  persons  under  various  circum- 
stances of  metabolic  expenditure,  climate,  etc.  To  a  great  extent  these 
experimental  products  and  the  data  derived  from  observations  of  actual 
corresponding  diets  very  closely  agree  in  all  essential  respects.  It  is 
agreements  of  this  sort  which  give  encouragement  in  the  often  slow 
progress  of  a  science. 

The  Exergy-values  of  Foods. — ^The  quantitative  work  referred 
to  has  been  accomplished  by  a  method  of  accurate  measurements  of  the 
energy-values  of  nutrients  in  relation  to  the  income  and  expenditure  of 
energy  by  animal  organism.  This  method  is  termed  calorimetry,  literally 
"heat-measurement,"  for  the  process  was  developed  in  studying  animal 
heat,  its  sources  and  mcxles  of  loss.  At  the  present  time  calorimetry 
means  the  accurate  measurement  of  the  energy-values  of  the  ingesta  of 
organisms,  oftentimes  in  relation  to  the  heating-energy  and  the  moving- 
energy  of  the  organisms.  In  its  theory  it  is  a  simple  method,  for  it  merely 
attempts  to  measure  the  income  and  expenditure  of  animals  (and 
latterly  of  plants  sometimes)   and  to  (k-termine    the   combustion-value 


THE  GENERAL  NATURE  OF  DIET 


141 


of  their  various  nutrients.  In  its  practice  elaborate  and  very  extensive 
apparatus  is  sometimes  required,  and  the  conduct  of  the  experiments 
involves  much  careful  complex  chemical  analysis  and  attention  to  the 
finer  points  of  several  branches  of  physics. 


Fig.  73 


^^■■:-:^ 

TABLE 

[Z]    GO    [ID 


TOOL 
CLOSET 

DRYING 

— 

'\^ 

General  plan  of  the  respiration-calorimeter  laboratory  of  the  United  States  Department  of 
Agriculture,  Washington.  This  diagram  is  self-explanatory,  so  far  as  the  principles  of  the  action 
of  the  calorimeter  are  concerned.      The  details  are  very  complex.      (Atwater.) 


142  FOODS 

The  unit  of  measurement  in  all  researches  of  this  sort,  very  necessary 
to  be  well  understood,  is  the  calorie  or,  formerly,  the  millecalorie  (yxrVo" 
part  of  the  calorie  proper).  Sometimes  one  unit  and  sometimes  the 
other  is  used,  but  they  are  so  unlike  in  size  that  confusion  can  scarcely 
arise.  A  calorie  is  the  quantity  of  energy,  expressed  as  heat,  necessary 
to  raise  the  temperature  of  one  kilo  (1000  gm.,  1000  c.c,  or  one  liter) 
of  pure  water  1°  C.  A  millecalorie  is  the  energy  in  the  form  of  heat 
needful  to  raise  1  c.c.  of  water  1°  C.  The  absolute  combustion-  or 
heat-value  of  any  nutrient  is,  then,  the  number  of  calories  of  energy 
liberated  by  its  complete  union  with  oxygen.  It  matters  not  a  bit 
whether  it  be  in  a  furnace  of  tlie  laboratory  or  in  the  circulation  and 
tissues  of  an  animal.  To  be  exact,  however,  oxidation  in  the  organism 
might  not  extend  to  every  particle  of  any  ingested  mass  of  food  even  if  all 
were  absorljed,  and  all  of  any  food  is  seldom  wholly  absorbefl.  There 
is  invariably  waste  of  one  sort  and  another,  as  the  composition  of  the 
feces  shows.  Still,  in  general  terms,  for  theory's  sake,  we  may  say  that 
any  given  quantity  of  food  gives  out  as  much  energy  when  consumed 
by  the  body  as  when  burned  in  an  ignition-tube.  It  has  been  one  of 
the  tasks  of  calorimetrists  to  ascertain  by  experiment  the  "combustion- 
equivalents"  of  all  important  articles  of  diet,  the  differences  between 
their  laboratory  comVjustion- values  and  their  intra-organic  energy-values 
being  so  small  as  to  be  negligiVjle.  A  complete  table  of  such  deter- 
minations has  less  interest  and  physiological  value,  however,  than  it 
would  have  were  the  conditions  of  organic  usefulness  in  oxidation  as 
simple  and  as  certain  as  those  methods  Ijy  which  these  tables  are 
derived. 

A  few  examples  will  suffice.  The  number  of  calories  of  heat  liberated 
in  the  burning  of  1  gm.  of  average  dried  bacon  is  8.86,  that  is,  in  the 
union  of  oxygen  with  1  gm.  of  bacon  just  enough  heat  is  liberated  to 
raise  the  temperature  of  8.86  liters  of  water  P  C.  Similarly,  the 
comVjustion-equivalent  of  fat  mutton  is  4.03  calories;  of  fat  beef,  3.27; 
of  white  bread,  2.74;  of  eggs,  1.59;  of  lean  beef,  0.98;  of  potatoes,  also 
0.98;  of  milk,  0.70;  of  apples,  0.74;  while  lettuce  yields  only  0.20  calories 
of  heat  per  gram.  Thus,  bacon  is  adapted  to  be  wisely  eaten  on  an 
active  day  in  winter,  anrl  lettuce,  apples,  and  milk  on  lazy  days  in 
.summer.  Experience  inherited  as  instinct  very  early  taught  many 
animals  this  dietetic  principle,  and  today  among  human  beings  it  has 
become  .settled  in  universal  custom.  Thus,  the  natives  of  the  tropics 
live  largely  on  juicy  fruits  and  vegetables,  while  the  inhabitants  far 
north  and  .south  of  the  equator  eat  great  amounts  of  fatty  meat  and 
even,  it  is  said,  oils  and  fat  in  quantities  which  would  be  nau.seating  to 
the  majority  of  mankind  nearer  the  equator. 

Just  as  every  actual  article  of  fowl  has  its  combustion-equivalent,  .so 
have  the  alimentary  proximate  principles,  proteid,  fat,  and  carbohy- 
drate. IiuVjner  found  by  actual  calorimetric  experiments  on  the  ti.s.sues 
(so  avoiding  the  more  uncertain  methofls  of  calctdation),  allowing  for 
energy  still  in  the  excreted  urea,  etc.,  that  the  following  three  focxl-com- 


THE  GENERAL  XATURE  OF  DIET  143 

ponents  bad    combustion-values  about  as  given  below.     These  deter- 
minations approximately  are  in  general  use  for  the  calculation  of  diets. 

COMHUSTION-EQUIVALEXTS    (PER    GKAXl). 

Average  proteid 4.1  calories. 

A\erage  fat 9.3  calories. 

Average  carbohydrate 4.1  calories. 

It  is  useful  to  know,  as  a  basis  of  comparison,  that  the  combustion- 
equivalent  of  1  gm.  of  hydrogen  is  34.622,  and  of  carbon  8.08.  In  order 
now  to  find  the  approximate  energy-value  of  any  given  mass  of  a  man's 
food  it  is  necessary  to  know  only  the  percentage-proportion  of  average 
proteid,  fat,  and  carbohydrate  in  it.  We  do  not  at  present  know  enough 
quantitatively  about  the  katabolism  of  the  inorganic  salts  and  the  water 
to  calculate  or  allow  for  them,  while  comparatively  few  foods  contain 
albuminoids  in  important  amount.  Having  learned  from  one  of  the 
standard  tables  (for  example  those  of  the  U.  S.  Agricultural  Department) 
the  percentages  of  fat,  proteid,  and  carbohydrate  present,  it  is  necessary, 
in  order  to  estimate  the  energy- value  of  the  composite  food,  only  to  mul- 
tiply each  component  by  its  combustion-equivalent  and  add  the  products. 
This  will  give  the  number  of  energy-calories  in  100  gm.  of  the  food, 
disregarding  salts,  water,  and  albuminoid  if  present.  As  an  illustration, 
take  a  kilo  (two-pound)  loaf  of  white  wheat  bread :  what  is  its  value  to  a 
hunter,  for  example,  as  nutriment?  In  every  100  gm.  of  the  bread 
there  are  about  8  gm.  of  average  proteid,  49.2  gm.  of  carbohydrate, 
and  only  1.5  gm.  of  fat  (hence  people  "naturally"  eat  butter  with  bread). 
The  salts  and  w^ater  as  energizers  we  disregard.  The  combustion- 
equivalent  of  average  proteid  is,  from  Rubner's  table  above,  4.1  of 
carbohydrate  4.1,  and  of  fat  9.3. 

8.0  multiplied  by  4.1  equals      .      .      .      .      32.80 

49.2  "  "4.1       " 201.72 

1.5  "  "9.3       " 13.95 


The  products'  sum  equals       .      .      .   248.47 

In  every  100  gm.  then  of  the  bread-sample  there  are  probably  avail- 
able for  the  eater's  warmth  and  strength  and  tissue-repair  248.47 
calories  of  energy.  Reduced  to  heat,  this  is  enough  to  raise  248.47 
liters  of  water  1°  C.  in  temperature.  In  the  supposed  kilo-loaf  there 
are  ten  times  as  many  calories,  or  a  total  of  2484.70  calories,  or  about 
two-thirds  the  "fuel,"  which  a  very  active  hunter  would  require  in 
winter  for  his  personal  "engine."  If  the  man  eats  100  gm.  of  butter 
with  this  loaf  of  bread  he  increases  his  food  materially,  and  both  in  a 
pleasant  and  an  easily  available  way.  A  dekagram  of  butter  properly 
made  consists  of  0.3  gra.  of  proteid,  91  gm.  of  fat,  besides  water  and 
salts,  but  no  carbohydrate.  From  the  0.3  gm.  of  proteid  (0.3  X  4.1) 
woukl    come    1.23    calories   of   energv,   and    from    the   91   gm.   of   fat 


144  FOODS 

(91  X  9.3)  S46.30  calories,  or  a  total  of  847.53  calories  from  100  gm.  of 
butter.  This  is  more  than  one-third  as  much  energy  as  was  afforded 
by  the  bread,  ten  times  as  heavy.  The  following  table,  compiled  by 
Atwater,  gives  a  fair  estimate  of  the  calorie-needs  of  men  performing 
various  degrees  of  labor. 

Dietetic  Needs  for  Various  Degrees  of  Labor. 
Conditions. 

Man  at  light  work 

Man  at  light  outdoor  work  

Man  at  moderate  outdoor  work        .... 

Man  at  hard  outdoor  work         

Man  at  very  hird  outdoor  work  in  winter 

United  States  army  ration 

United  States  na-\y  ration 

College  football  team 

Teamsters  and  marble-cutters  in  Boston,  Mass. 
Laborers  of  Lombardv,  Italv 


Prn+piH 

Fat. 

Carbo- 

Energ3' in 

hydrate. 

calories. 

110 

60 

390 

2634.2 

110 

100 

400 

3052.0 

125 

125 

450 

3556.0 

150 

150 

500 

4105.0 

180 

200 

600 

5008.0 

120 

161 

454 

3851.0 

143 

184 

520 

4998.0 

181 

292 

557 

5742.0 

254 

363 

826 

7804.0 

82 

40 

362 

2192.0 

We  shall  have  a  little  more  discussion  of  the  quantitative  adaptation 
of  diets  later  on  (p.  151).  Even  the  last  two  diets  summarized  in  the 
above  table  are  not  the  extremes  of  actual  diets  in  the  overcivilized 
countries  of  Europe  and  of  America.  Playfair  reported,  about  thirty- 
five  years  ago,  a  London  sewing-girl  with  weekly  earnings  of  three  shill- 
ings ninepence,  who  .subsisted  on  53  gm.  of  proteid,  33  gm.  of  fat,  and 
316  gm.  of  carbohydrate,  a  diet  theoretically  worth  only  1S20  calories. 
The  physiological  conditions  which  made  life  on  so  little  fuel  possible 
are  obvious.  The  individual  w^as  a  female,  doubtless  not  tall,  certainly 
very  thin,  with  a  relatively  small  amount,  therefore,  of  tissue-waste. 
Her  labor  had  in  it  almost  a  minimum  of  both  bodily  and  mental 
exerci.se,  and  was  carried  on  almost  if  not  quite  wholly  indoors.  It  was 
done  doubtless  in  that  spiritless  and  feeble  way  characteristic  of  any 
machine,  natural  or  artificial,  with  little  power  behind  it.  At  the  other 
extreme,  Atwater  found  in  Cambridge,  ]\Iassachus vtts,  brickmakers  who 
daily  con.sumed  ISO  gm.  of  proteid,  365  gm.  fat,  and  1150  gm.  of 
carbohydrate,  giving  altogether  8848  calories  of  energy.  These  are 
indeed  extremes — that  of  the  little  seamstress  almost  a  starvation, 
indoor  diet  barely  enough  to  keep  body  and  .soul  together,  while  that 
of  the  brickmakers  is  the  almost  gluttonous  diet  of  well-paid  workmen, 
in  one  of  the  most  laborious  of  outdoor  trades. 

Using  the  combustion  values  of  proteid,  fat,  and  carbohydrate  already 
given,  the  average  food-requirements  as  estimated  by  seven  older  authori- 
ties, give  the  following  averages:  Of  dry  proteid,  according  to  these  older 
figures,  about  121  gm.  is  required,  of  dry  fat  about  59  gm.,  and  of  dry 
carbohydrate  510  gm.  To  these  numbers  .should  be  added  30  gm.  of 
inorganic  salts  and  3  liters  of  water.  The  recent  work  by  Chittenden 
anrl  some  others  makes  it  fairly  probable  that  the.se  amounts  are  exces- 
sive as  a  grand  average  requirement  for  the  average  adult  human  Vjeing. 
It  has  lateiv  been  claimefl   that  man  does  not  masticate  his  food  .suffi- 


THE  GENERAL  NATURE  OF  DIET  ]45 

ciently,  and  that  if  he  chewed  it  more  he  would  get  from  it  much  nutriment 
which  is  now  wasted.  These  more  recent  researches  would  tend  to  cut 
down  the  average  requirements  of  proteid  40  per  cent.,  or  even  more. 
It  is  believed  by  many  physiologists,  however,  that  to  do  this  would  so 
decrease  the  working  surplus,  so  to  say,  of  the  individual's  food-income 
that  emergencies,  such  as  illness,  would  be  much  more  dangerous  to  a 
person  who  had  lived  on  this  quantity  of  food .  It  remains  to  be  seen,  then, 
by  further  research  on  a  much  larger  scale  and  lasting  a  much  longer 
time  how  much  food  an  average  adult  actually  neefls.  Here  as  elsewhere 
the  relations  are  more  widespread  and  more  complicated  than  the  experi- 
mental conditions  take  account  of. 

The  Right  Proportion  of  the  Diet's  Components  is  Important. — The  third 
general  requirement  of  diet  is  that  its  proximate  principles  should  be  in 
nearly  the  proportion  best  suited  to  the  organism's  needs.  In  the  average 
published  heretofore  by  these  seven  authorities  recently  mentioned,  the 
proteid  was  about  17  percent.,  the  fat  about  8.5  percent.,  and  the  carbo- 
hydrate about  74  per  cent.,  if  we  neglect  the  inorganic  salts  and  the  water. 
The  whole  principle  underlying  the  right  proportion  of  proximate  prin- 
ciples in  food  is  that  an  excess  of  one  of  them  in  the  diet  necessitates  the 
useless  expense  of  energy  to  digest  and  absorb  this  excess.  In  general 
terms,  only  milk  and  eggs  contain  the  proximate  principles  in  just  the 
right  proportion.  White  bread  perhaps  approaches  this  condition  next 
best.  Rice,  for  example,  contains  about  one-third  the  ideal  proportion  of 
nitrogen.  The  person  who  is  compelled  to  live  upon  it  continually,  there- 
fore, has  to  burden  his  digestive  apparatus  with  a  large  excess  of  carbohy- 
drate (almost  wholly  starch).  In  some  South  American  tribes  the  diet 
was  formerly,  at  least,  almost  wholly  meat.  These  people  would  have  to 
eat  a  large  excess  of  the  flesh  to  get  a  sufficient  amount  of  carbohydrate. 
In  the  Arctic  regions  the  diet,  on  the  other  hand,  is  largely  fat,  and 
carbohydrate  might  often  be  lacking  in  a  diet  in  this  region.  In  order  to 
obtain  these  deficient  proximate  principles,  an  excess  of  the  others  must 
be  digested  and  absorbed,  only  to  be  excreted  again  unused.  All  of  these 
processes  (mastication,  deglutition,  digestion,  absorption,  excretion,  etc.) 
use  up  many  varied  forms  of  energy  which  might  be  better  employed. 

Variety  in  the  Diet  is  Necessary. — A  fourth  requirement  of  a  proper 
diet  is  that  it  should  consist  of  a  considerable  variety  of  foods.  This 
exaction  of  Nature  in  its  effects  on  the  world's  diet  is  not  unlike  the 
preceding  demand  that  the  proportions  of  the  alimentary  components 
should  not  depart  too  far  from  the  composition  of  the  consumer's  body. 
The  ingestion  of  a  large  variety  of  foods  in  practice  assures  this  right 
proportion.  But  several  other  things  involved  in  the  matter  of  variety 
are  as  yet  unconsidered,  and  especially  the  preparation  of  food-materials 
for  being  eaten  by  man. 

It  is  not  enough  that  an  animal's  diet  shoidd  contain  both  energizers 

and  sources  of  tissue-replacement,  or  that  it  should  consist  of  a  sufficient 

quantity  of  the  proximate  principles  of  the  animal  tissues,  even  if  nearly 

or  quite  in  their  proper  proportions.     ^Nlost  of  the  brutes,  to  be  sure, 

10  . 


14G  FOODS 

would  continue  to  live  very  well  on  a  diet  thus  describable.  By  force  of 
poverty  or  other  adverse  conditions  millions  even  of  men  and  women 
subsist  their  lives  tlu-ough  on  a  very  few  of  the  staple  articles  of  food,  such 
as  rice  and  other  starchy  nutrients.  We  are  trying  to  become  familiar, 
however,  with  an  ideal  diet  physiologically  adapted  to  such  men,  women, 
and  children  as  most  of  us  are  concerned  with  in  civilized  (perhaps 
overcivilized)  modern  lands.  To  men  who  are  more  than  the  victims  of 
an  unkind  nativity  and  more  than  animals,  variety  in  their  food  is 
important,  indeed  practically  essential.  We  might  even  go  farther  and 
maintain  that  the  basal  requirements  of  composition  being  always 
satisfied,  the  greater  the  variety  in  the  food  the  better  is  the  organism 
served  by  it.  In  obtaining  an  understanding  of  the  facts  and  principles 
of  digestion,  in  the  next  chaper  we  shall  see  that  the  conditions  under 
which  the  softening  and  hydrolyzing  secretions  of  the  alimentary  canal 
are  augmented  or,  on  the  other  hand,  inhibited  are  very  intricate.  This 
might  be  expected  in  an  organism  as  uniquely  complex  as  that  of  man,  com- 
bining in  its  functions  mind  as  well  as  body.  Even  if  the  tissue-cells 
are  supplied  with  what  they  demand  of  food  quantitatively  as  well  as 
qualitatively,  the  mechanism  which  immediately  furnishes  to  them  this 
nutriment  is  discriminative.  Because,  perhaps,  of  its  close  connection 
with  the  sensitive  brain  it  soon  demands  a  change  in  the  quality  of  its 
supplies  when  forced  to  work  on  a  small  series  of  foods.  We  tire  of 
almost  all  sorts  of  food  eaten  to  excess,  and  the  more  quickly  the  greater 
the  sameness  and  the  stronger  the  flavors.  The  organism's  require- 
ments are  in  this  respect,  out  of  many,  self-regulating,  and  on  the  one  side 
demand  that  the  foods  shall  be  not  too  much  alike  in  taste  (and  to  a  less 
extent  in  odorj,  and,  on  the  other  hand,  that  they  shall  be  not  too  strongly 
flavored.  So,  as  a  practical  outcome  of  this  natural  tendency,  we  see  that 
wheat-bread  and  the  staple  sorts  of  meat,  eggs,  milk,  plain  soups,  and 
vegetables,  feebly  flavored,  constitute  the  great  bulk  of  our  usual  diet. 
Sugar  is  an  important  nutrient  which  is  almost  an  exception  to  this  rule, 
for  exceedingly  few  or  no  individuals  of  the  animal  kingdom,  from  insects 
to  man,  young  or  old,  seem  ever  to  weary  of  its  sweetness.  Indeed ,  this  is 
a  word  in  all  languages  adopted  metaphorically  for  delight  and  pleasant- 
ness. It  is  of  small  account  if  any  new  article  of  food  has  an  unpleasant 
flavor,  for  when  familiar,  such  a  flavor  becomes  pleasant.  As  no  two 
articles  of  food  taste  cjuite  alike,  the  natural  way  to  obtain  this  variety 
of  flavor  with  its  consequent  and  more  important  variety  of  composition, 
is  to  use  as  nutrients  many  sorts  of  substances,  mineral,  vegetable,  and 
animal,  from  many  various  places,  earth  and  air  and  sea.  The  organism 
naturally  is  after  a  wide  variety  of  elementary  and  compound  materials 
which  in  their  union  in  the  gut  shall  always  form  an  average  pabulum 
ample  and  nearly  invariable  in  its  absorbable  products.  By  this  wide- 
gathering  of  many  substances  whose  limits  of  strangeness  are  guarded 
by  taste  and  smell  and  the  sense  of  nausea,  the  organism  best  secures  its 
ends  in  tliis  respect.  We  have  seen  already  the  chemical  basis  of  this 
unity-in-variety,  and  it  needs  no  further  elaboration. 


THE  GEXERAL  NATURE  OF  DIET  147 

The  variety  required  is  not  only  the  diversity  of  a  day  or  a  week,  but 
also  of  each  meal,  as  is  the  custom  more  or  less  everywhere.  A  large 
variety  at  a  meal  is  necessitated  more  by  the  pleasure  arising  from  the 
varied  flavors  than  from  the  precise  needs  of  the  organism  from  hour  to 
hour.  Let  us  look  a  little,  then,  at  the  nature  of  the  diversity  in  a  well- 
cooked  meal  as  regards  its  chemical  components,  its  digestibilitv,  its 
flavors,  and  its  odor.  We  may  take  for  this  purpose  a  dinner  such  as  is 
served  at  an  average  American  hotel;  this  will  answer  several  purposes 
at  once.  The  first  thing  most  people  from  habit  wish  after  being  seated 
at  the  table  is  two  or  three  swallows  of  cold  water,  and  this,  undoubtedlv, 
slightly  stimulates  the  salivary  glands  and  the  mucosa  of  the  stomach  and 
prepares  the  taste-organs  for  better  action.  The  first  food  brought,  we 
w'ill  suppose,  is  bouillon  and  bread  and  butter.  This  soup  is  at  once 
nutritious,  tasteful,  and  of  pleasant  odor,  the  two  latter  qualities  coming 
largely  from  the  "extractives,"  salts,  and  soluble  albumins  which  it  con- 
tains, the  nutritive  value  from  its  richness  in  most  of  the  proteids  of  beef. 
Soup  serves  by  its  heat,  liquidity,  and  salts  to  warm  and  stimulate  gently 
the  glands  and  walls  of  the  stomach  and  duodenum  in  preparation  for 
solid  food.  The  bread  adds  physical  substantiality  to  the  liquid  food, 
w^hile,  as  already  noted,  the  butter  adds  the  fat  lacking  in  the  bread, 
makes  the  latter  more  pleasant  to  the  taste,  and,  when  melted  in  the 
mouth,  more  easily  swallowed.  Between  the  soup  and  the  fish  the  short 
interval  of  waiting  is  an  advantage,  a  distressing  sense  of  hurry,  leading  to 
indigestion,  being  thus  avoided  when  time  for  eating  is  normally  abun- 
dant. Fish  contains  mostly  proteids  and  fat,  and  potatoes  are  eaten  with 
it  to  supply  the  lacking  carbohydrate.  A  little  of  some  strongly  flavored 
condiment  or  relish,  a  pickle  or  an  olive  or  two,  often  serves  at  this  point  in 
a  dinner  to  still  more  vigorously  stimulate  the  digestive  glands  (by  means 
of  the  pepper,  mustard,  horseradish,  acid,  etc.,  which  they  contain)  in 
readiness  for  the  ipiece  de  resistance,  the  flesh-meat,  more  difficult  of  diges- 
tion than  ordinary  fish.  This  also,  as  in  case  of  the  fish  and  for  like  reason, 
is  served  with  potatoes,  most  often  baked,  and  if  properly  cooked  is  to 
most  persons  the  most  pleasant  as  well  as  the  most  substantial  portion 
of  the  meal.  The  seasonable  vegetables,  peas,  beans,  spinach,  squash, 
or  what  not,  add  each  its  flavor,  its  salts,  its  juice,  and  its  quota  of  starch 
and  proteid  to  the  food ;  these  are  best  handled  by  the  digestive  mechanism 
while  in  the  full  vigor  of  the  meal's  solution.  Two  or  three  glasses  or  even 
more  of  cool  but  not  ice-cold  water  mav  have  been  drunk  during-  the 
meal  thus  far  with  pleasant  eflfect.  The  pastry  and  dessert  and  a  cup  of 
coffee  are  now  served.  The  second  if  not  the  first  usually  contains  much 
sugar,  and  being  in  other  ways  intended  to  be  delicious  to  the  taste,  thus 
adds  almost  the  finishing  touches  to  the  pleasant  sense  of  "fulness"  or 
satiety  which  usually  accompanies  the  satisfaction  of  basal  organic 
needs  by  normal  functioning.  A  cup  of  coffee  adds  still  more  to  the 
licjuid  and  heat  of  the  digesting  meal,  both  beneficial  factors,  w^hile  its 
essential  alkaloid,  caffeine,  stimulates  gently  the  whole  organism, 
especially  the  nerves  and  the  muscles.    If  a  mild  cigar  be  smoked  after 


148  FOODS 

the  dinner,  as  an  incentive  to  social  chat  with  crenial  companions,  the 
orcjanism  is,  thereby,  still  further  stimulated  into  a  condition  of  quiet 
digestive  activity,  with  mental  musing  and  muscular  rest,  the  condition 
best  adapted  for  the  quick  and  pleasant  digestion  of  a  meal. 

The  feeling  of  satiety  which  follows  the  eating  of  a  full  dinner  or  other 
repast  has  some  little  physiological  interest.  It  is  especially  noticeable 
when  a  large  quantity  of  food  has  been  taken  slowly,  accompanied  by  hot 
tea,  coffee,  or  cocoa,  and  ending  with  a  sweet  dessert.  It  arises  doubtless 
from  the  functional  congestion  of  the  stomach  and  small  intestine  with 
its  accompanying  internal  warmth;  the  muscular  and  glandular  activity 
add  that  tone  of  pleasantness  which  exercise  of  whatever  sort  always 
produces  in  a  normal  organ.  This  feeling,  however,  cannot  be  regarded 
as  the  necessary  criterion  of  a  sufficient  meal,  for  long  before  the  stomach 
is  so  full  as  to  occasion  this  sensation  the  needs  of  the  body,  if  supplied 
three  times  a  day,  have  been  satisfied.  It  may  be  taken,  however,  to  some 
degree,  apparently  as  the  index  or  criterion  of  a  properly  balanced  meal, 
all  parts  of  the  digestive  mechanism  proper  being  then  put  in  activity. 

As  in  other  human  affairs,  the  common-sense  usefulness  of  ordinary 
diet  is  at  times  disturbed  for  even  a  considerable  number  of  persons  by  the 
influence  of  new  and  radical  theories  and  fads,  not  to  mention  the  host 
of  proprietary  foods  which  are  continually  appearing.  Certain  that 
actually  new  nutrients  are  little  apt  to  appear,  scientific  dietetics  pays 
little  heed  to  the  extreme  theories,  save  to  combat  them.  It  welcomes, 
however,  every  new  form  of  adequate  nutriment  as  one  further  addition 
to  the  variety  of  foods,  all  useful  at  some  time  or  other.  For  example, 
the  recent  large  number  of  brands  of  prepared  cereals,  etc.,  is  a  distinct 
advantage  to  the  public  who  can  buy  them,  for  they  make  it  certain  that 
almost  anyone  can  eat  month  after  month,  as  part  of  their  breakfast, 
some  delectable  and  substantial  grain-product,  whereas  not  so  many 
years  ago  to  be  tired  of  three  or  four  was  to  be  tired  of  them  all. 

The  most  usual  dietetic  objection  to  eating-fads  generally  is  that, 
even  if  the  methods  or  the  foods  suggested  supply  the  needful  nutrients, 
their  use  tends  to  decrease  the  variety  and,  by  consec(uence,  the  value 
of  one's  diet.  They  foster  the  harmful  and  disturbing  habit  of  attending 
to  the  digestive  process,  and,  like  other  fads,  direct  the  individual  more 
or  less  toward  the  unl)a]ance  of  fixed  or  of  imperative  ideas.  The  most 
widespread  of  the  diet-fads  is  vegctarlmii.sm.  It  arose  in  the  P^astern 
countries  aj)parently  })ecause  of  tlie  influence  brought  from  Buddhistic 
India,  which  makes  it  seem  murder  to  kill  the  brute-animals  because 
supposedly  animated  by  transmigrated  human  souls.  Hereabouts,  by 
Christian  people,  it  is  construed  merely  as  a  belief  in  the  sacredness  of 
I^rute-iife  or  as  a  feeling  of  natural  pity.  One  sees  the  same  point  of 
view  as  an  innate  emotion  in  young  children  sometimes,  an  exaggeration 
of  the  validity  of  the  purely  sentimental  over  that  of  the  valuable  and  the 
practical.  AVgetarians  are  of  two  sorts,  real  and  self-fancied,  consistent 
vegetarians  and  mejck-vegetarians,  as  they  are  termed.  The  latter  we 
need  not  here  notic-e,  for  they  are  mere  zoophilic  j)retenders  in  that  they 


THE  GKXERAL   NATURE  OF  DIET  149 

eat  the  two  most  characteristic  of  all  animal  foods,  eg^js  and  milk.  Con- 
sistent vegetarians  are  omnivorous  animals,  who  trv  to  make  themselves 
into  herbivora.  Some  of  them,  so  far  as  the  source  of  their  food  is  con- 
cerned, succeed  in  this  endeavor,  but  only  at  no  little  cost  in  force  to 
themselves.  For  this  extravagance  of  organic  force  there  are  three  main 
causes:  (1)  The  relative  great  difficulty  in  general  of  masticating  and 
digesting  the  proteid  out  of  cereals,  lentils,  vegetables,  and  fruits,  as 
comparetl  with  that  from  fish  and  meat,  eggs,  and  milk.  (2)  The  rela- 
tively small  absorbability  of  the  alimentary  proximate  principles  derived 
from  foodstufts  other  than  animal.  The  table  compiled  by  Atwater 
(page  137)  shows  the  second  of  these  objections  well,  and  in  particular  the 
fact  that  from  animal  foods  9S  per  cent,  of  the  proteid,  97  per  cent,  of 
the  fat,  and  100  per  cent,  of  the  carbohydrates  is  absorbed  into  the  cir- 
culation and  utilized,  while  from  other  sorts  of  foods  an  average  of  only 
82.5  per  cent,  of  proteid  is  absorbed,  90  per  cent,  of  the  fat,  anfl  96.5 
per  cent,  of  the  carbohydrate.  The  greatest  loss,  then,  is  in  proteid,  and 
in  the  struggle  for  existence  of  the  multitude  of  men  this  actual  loss  of 
15.5  per  cent,  is  of  considerable  importance,  of  far  greater  moment 
certainly  than  are  the  lives  of  certain  animals  which  never  would  have 
lived  at  all  unless  raised  solely  for  this  high  and  biological  purpose  of 
feeding  man  and  other  animals.  One  has  only  to  glance  at  the  teeth  of 
man,  comparing  them  with  those  of  cattle  and  of  dogs  (page  165),  and  to 
understand  the  rudiments  of  the  digestive  chemistry  of  the  various  sorts 
of  animals,  to  be  assured  that  the  whole  human  organism  is  naturally 
omnivorous:  carnivorous  quite  as  much  as  herbivorous. 

Cookery. — The  variety  of  foods  which  most  of  the  brutes  naturally 
use  is  small.  What  they  shall  eat  is  largely  predetermined  by  instinct, 
by  the  chance  of  what  happens  to  be  near  and  by  habits  originated  by 
these  other  two  conditions.  The  food-range  of  carnivora  is  doubtless 
larger  than  that  of  herbivora,  while  naturally  the  range  of  omnivora, 
like  many  fishes  and  birds  and  man,  is  larger  than  that  of  those  species 
which  use  only  plants  or  only  animals.  ]Man's  intelligence  doubtless 
would  have  led  him  directly  to  have  tried  many  sorts  of  food,  but  it  cer- 
tainly has  taught  him  one  great  art  which  has  accomplished  the  same 
important  result  indirectly,  and  which,  as  much  as  any  other  thing, 
biologically  differentiates  him  from  his  "poor  relations,"  the  brutes. 
This  art  is  that  of  cookerij,  of  preparing  food  for  the  pleasurable  nourish- 
ment of  man  and  other  animals.  In  this  definition  of  cookery  three  wortls 
are  emphatic :  "Preparing,"  indicating  the  wide  range  of  the  art ;  "pleasur- 
able," suggesting  one  of  its  important  purposes;  and  "nourishment," 
indicating  its  basal  usefulness,  and  the  essential  requisite  of  all  proper 
cookery.  The  range  of  the  art  of  the  cook  is  wide,  physiologically  at  least, 
for  it  includes  as  certainly  the  proper  care  of  milk  and  the  sterile 
cleansing  of  lettuce  as  the  concoction  of  a  seashore  chowder  or  the  proper 
roasting  of  a  turkey.  It  is  the  cook's  proper  business  to  be  in  a  position 
to  guarantee  to  his  trustful  clients  the  atlequate  nourishment,  the  pleasant 
flavor,  and  the  entire  safety  of  the  food  he  prepares  for  them.    The  last 


150 


FOODS 


requirement  is  seemingly  often  overlooked,  ancf  with  dire  effect.  The 
importance  of  the  art  of  cookery  to  mankind  can  scarcely  be  overesti- 
mated. To  the  trained  nurse,  the  nursery-maid,  and  the  physician 
few  things  are  more  important,  but  at  present  the  last  learns  scarcely 
more  about  it  than  the  second,  and  not  nearly  as  much  as  does  the  first. 
In  many  diseases,  and  for  more  and  more  with  the  increasing  number  of 
antitoxins,  the  proper  feeding  of  the  patient  is  three-quarters  of  his 
proper  treatment,  and  to  direct  this  proper  feeding  intelligently,  the 
physician  requires  a  practical  as  well  as  a  theoretical  knowledge  of  foods 
and  their  ideal  preparation.  Every  medical  curriculum  might  not 
improperly  include  a  demonstration-course  in  actual  cookery  to  complete 
its  discussion  of  food  and  dietetics. 

The  preparation  of  food  for  man  includes  the  boiling,  stewing,  roasting, 
baking,  broiling,  frying,  preserving,  freezing,  brewing,  and  arranging 
of  soups,  meats,  breads,  vegetables,  salads,  pastry,  desserts,  preserves, 
ices,  fruits,  and  beverages.  We  will  consider  the  chief  of  these  culinary 
processes,  and  especially  their  relations  to  the  physiological  value  of  food. 


Fig.  74 


Changes  of  starch-cells  in  cooking:  a,  cells  of  raw  potato  with  starch-grains  in  natural  con- 
dition; b,  cells  of  a  partially  cooked  potato;  c,  cells  of  a  thoroughly  boiled  potato.  (United 
States  Department  of  Agriculture  Year-book,  1900. 

In  general,  the  application  of  heat  to  food  more  or  less  (1)  destroys 
the  cellulose  shell  about  the  grains  of  starch  in  carbohydrates,  coagulates 
some  proteids  and  dissolves  others,  and  softens  the  fat;  (2)  macerates 
and  makes  more  easily  masticable  flesh  and  vegetables;  (3)  destroys 
parasites  of  nearly  all  sorts ;  (4)  renders  the  food  more  grateful  both  to 
the  taste  and  to  the  intestines  by  its  warmth;  and  (5)  develops  flavors, 
especially  in  meats. 

Of  all  modes  of  cooking,  hoiling  is  undoubtedly  the  most  common, 
it  being  easiest  and  cheapest.  Boiling  differs  from  stewing  only  in  degree, 
for  the  latter  process  is  boiling  continued  until  the  food  falls  apart  from 
solution  of  the  connective-tissue  of  meats  or  of  the  rough  cellulose  frame- 
work of  vegetables.  The  boiling  water  penetrates  the  mass  of  food  and 
cooks  it  homogeneously,  and  so  differs  much  in  its  effects  from  roasting 
or  broiling,  lioiled  meats  are  le.ss  easily  digestible  than  those  roasted 
or  broiled,  for  the  soluble  proteids  are  coagulated  and  rendered  hard  and 


THE  GEXERAL  NATURE  OF  DIET  151 

relatively  tasteless,  while  the  salts  and  savory  extractives  pass  largely 
into  the  water.  Prolonc^ed  boiling  may  redissolve  some  of  the  coagulated 
proteids.  In  boiling,  unless  umler  pressure,  the  temperature  does  not 
exceed  100°  C.  Boiling  is  chiefly  important  as  a  means  of  cooking  vege- 
tables, for  it  makes  starchy  foods  available  as  food  which  raw  woidd  be 
quite  indigestible  and  even  irritating  to  the  gut.  In  the  processes  of 
roasting  and  broiling,  essentially  alike  in  action,  the  material  should  be  at 
first  subjected  to  a  high  degree  of  heat,  200°  or  higher.  This  coagulates 
the  outside  of  the  mass  into  a  sort  of  shell,  which  retains,  more  or  less 
unchanged,  the  juices  and,  in  case  of  meat,  the  salts,  extractives,  and 
soluble  albumins.  Flesh  which  has  been  heated  not  above  70°  is  the 
most  digestible,  for  even  this  degree  of  heat  changes  the  connective- 
tissue  which  binds  the  muscle-bundles  together  to  gelatin  and  renders 
the  meat  more  easily  masticated.  The  high  heat  of  the  first  part  of 
roasting  also  develops  in  the  fats  of  the  meat  several  very  savory  fatty 
acids,  and  thus  provides  usefid  flavors  not  otherwise  obtained.  In 
frying,  the  heat  is  conveyed  to  the  interior  of  the  food  by  means  of  melted 
fat  of  various  sorts,  commonly  lard,  butter,  or  suet.  This  provides  a 
very  high  degree  of  heat  which  more  or  less  penetrates  the  mass  and 
produces  efl"ects  somew^hat  like  those  of  prolonged  and  excessive  baking 
or  roasting.  The  fat,  however,  tends  to  surround  with  a  film  each  par- 
ticle of  the  meat  or  vegetable,  and  so  renders  it  relatively  indigestible. 
The  excessive  use  of  fried  food,  caused  by  its  relative  ease  and  cheapness, 
is  one  of  the  curses  of  American  habits  of  cooking,  it  being  often  used 
when  broiling  would  be  very  much  better  for  the  consumer.  Preserving 
is  a  mode  of  preparing  food  so  that  it  will  keep  indefinitely.  It  consists 
usually  of  some  process  of  sterilizing  (commonly  by  heat),  the  material 
being  then  sealed  from  the  putrefactive  germs  of  the  air.  In  jellies  the 
sugar  acts  as  a  preservative.  Almost  every  sort  of  meat,  vegetable,  and 
fruit  is  now  thus  prepared  in  glass  or  in  tin,  and  so  made  for  indefinite 
periods  of  time  available  in  any  part  of  the  world.  In  some  cases  the  use 
of  artificial  preservative  substances  renders  the  foods  so  prepared  difficult 
of  digestion,  but  most  of  the  objections  made  on  this  score  seem 
unfounded.  .  The  elaborate  test-experiments  made  by  the  United  States 
Government  chemists  tended  to  the  principle  that  w^hile  boric  acid,  for 
example,  would  probably  irritate  a  digestive  apparatus  unduly  if  taken 
in  considerable  quantities  continuously,  in  the  amount  apt  to  be  ingested 
by  the  average  person  on  an  average  diet  practically  no  harm  would 
ensue.  The  cold-storage  problem  (fowls,  for  example,  often  being  kept, 
it  is  said,  two  years  or  more)  is  in  practice  a  more  important  question. 
However  low  the  temperature,  in  time  protoplasm  probably  undergoes 
degeneration,  which  makes  it  more  and  more  unsuitable  for  human  food. 
The  smoking  of  flesh-meats,  including  fish,  and  the  drying  of  meats, 
vegetables,  and  fruits  is  a  valuable  mode  of  preserving  food  for  a  shorter 
period  than  in  case  of  hermetical  sealing  from  the  air.  Nutrients  so 
prepared  are  liable  to  be  infested  by  worms  and  by  mould,  and,  in  many 
cases,  at  least,  are  relatively  lacking  in  flavor,  except  that  of  salt  or  of  the 


152  FOODS 

volatile  substances  of  smoke.  The  hrewing  of  beverages,  such  as  coffee, 
tea,  cocoa,  and  beers,  consists  either  in  the  making  of  a  decoction  (as  in 
tea  and  coffee) ;  of  a  solution  which  is  then  cooked  (cocoa  and  chocolate) ; 
or  in  the  fermentation  of  the  sugars  in  many  vegetable  substances  (of 
which  barley  is  typical)  under  the  influence  of  yeast  (Saccharomycetes 
cerevisice).  Freezing  is  a  culinary  method  which  has  come  into  common 
use  only  of  late  years,  but  it  affords  many  desserts  nourishing  and  grateful 
to  the  well,  and  often  very  valuable  in  febrile  disorders.  The  use  of  ices 
is  rapidly  increasing  in  Europe  as  well  as  in  America,  where  the  art 
originated. 

Quantitative  Adaptation  to  its  Service  is  Essential. — Another  require- 
ment in  an  ideal  diet  is  that  it  should  be  adapted  quantitatively  in  some 
degree  to  the  conditions  under  which  it  is  employed.  As  has  already 
been  emphasized,  a  food  provides  energy  for  the  warming  and  the  mov- 
ing of  the  body  and  materials  for  the  replacement  of  wornout  and  excreted 
tissue.  The  greater  then  (a)  the  amount  of  muscular  and  neural 
exercise,  the  greater  (b)  the  atmospheric  opposition  for  keeping  warm, 
and  the  greater  (c)  the  need  of  new  tissue,  whether  for  growth  or  for 
tissue-waste,  the  greater  the  amount  of  food  required.  This  is  axiomatic, 
but  it  is  important  in  dietetics.  The  only  reason,  in  practice,  that  there  is 
observed  no  greater  differences  in  the  amount  of  food  consumed  by,  say, 
the  idle  "society  woman"  and  the  street-laborer  is  that  the  former  prob- 
ably eats  far  too  much,  while  the  latter,  owing  chiefly  to  his  small  income, 
perhaps  eats  somewhat  too  little.  The  status  of  mental  labor  as  regards 
the  amount  of  food  recjuired  is  at  present  in  a  somewhat  uncertain  con- 
dition theoretically.  We  do  not  know  exactly  how  much  energy  and 
tissue  the  brain's  activity  actually  consumes.  Researches  now  being 
performed  on  men  with  balances  large  enough  to  support  a  man  and  yet 
exceedingly  delicate,  will  doubtless  determine  the  amount  of  tissue  lost 
in  mental  work.  Calorimetric  measurements  of  the  energy  expended  in 
mental  activity  have  given  thus  far  no  important  results.  So  far,  then, 
we  cannot  make  as  close  a  correlation  between  the  amount  of  brainwork 
and  the  food-recjuirements  as  is  made  between  muscle-work  and  the 
necessarv  amoimt  of  food.  The  cortex  cerebri  in  the  averao^e  man  weie-hs 
about  17  gni.,  while  the  muscles  in  an  average  sized  man  weigh  about 
33,000  gm.  This,  obviously,  is  the  cause  of  the  difference  noted.  It  is 
likely  that  the  nervous  system  per  gram  wastes  faster  and  gives  out  more 
energy  than  does  muscle.  (For  an  estimate  of  the  work  done  by  the 
human  heart  see  page  279.) 

The  colder  the  atmosphere  in  which  an  organism  lives  the  more  heating 
fuel  it  will  require,  and  the  (juantity  of  food  needs  adaptation  to  this 
condition  to  some  extent.  Part  of  the  body-heat  comes  from  muscular 
exercise,  so  that  the  metabolism  in  general  tends  to  be  more  active  in  a 
cold  atmosphere,  and  tissue-waste  is  thus  increased.  Again,  heat  is 
lost  by  radiation  and  conduction  from  the  skin  more  rapidly  on  a  cold 
day  than  on  a  warm  day,  and  this  excess  of  loss  the  foofi  must  supply. 
Of  the  2500  calories  of  energy  which  an  average  man  daily  receives  from 


THE  (iEXERAL  XATVRE  OF  DIET  153 

his  food,  at  least  five-sixths  are  expended  in  warminjj  the  body  to  its 
constant  temperature.  A  large  part  of  this  is  expended  from  the  skin. 
Any  variation  in  the  radiation,  conduetion,  and  evaporation  from  the 
skin,  therefore,  would  markedly  affect  the  amount  of  food  re(|uired.  In 
bodies  of  the  same  general  shape,  but  of  diiferent  size,  the  surface  area 
is  much  larger  in  proportion  to  the  mass  in  a  smaller  body  than  in  a  larger 
one.  It  is  by  the  mass  that  the  heat  is  produced,  and  by  the  surface 
area  that  it  is  largely  lost.  It  is  on  this  principle  partly  that  a  child 
requires  proportionally  much  more  food  than  does  an  adult.  A  male 
baby  of  one  year  requires  nearly  twice  as  much  food  proportionally  to  his 
weight  as  does  the  man  twenty  years  okl  doing  moderate  muscular  work. 
Another  factor  in  this  difference  is  the  greater  activity  of  the  metabolism 
in  children.  Moreover,  in  early  life  the  body  is  growing  larger,  and  more 
food  is  recjuired  on  this  account. 

In  general  terms,  then,  the  man  who  works  with  his  muscles  outdoors 
in  winter  requires  the  largest  amount  of  food ,  while  the  man  who  works 
with  his  brains  indoors  requires  proportionally  the  smallest  amount  of 
food.  As  we  have  noted,  how^ever,  the  latter  individual  consumes  more 
nearly  the  food  that  the  former  consumes  than  what  we  might  expect 
theoretically.  It  remains  to  be  seen  by  further  research  whether  the 
indoor  brain-worker  in  particular  actually  eats  on  the  average  more  than 
he  needs. 

Qualitative  Adaptation  in  Certain  Physiological  Conditions  is  Valuable. 
— The  last  demand  in  an  ideal  diet  which  was  suggested  was  that  the 
food  during  certain  physiological  periods  and  conditions  shoukl  be 
adapted  qualitatively  to  their  respective  needs. 

Stating  the  matter  in  this  way,  the  implication  is  conspicuous  that, 
save  in  these  circumstances,  diet  should  not  be  adapted  qualitatively. 
Such  undoubtedly  is  the  case.  Fi'om  considerations  already  discussed, 
it  is  obvious  that  it  is  part  of  the  power  peculiar  to  protoplasm  to  select 
for  itself  out  of  the  circulation's  general  store  of  paljulum  that  which  it 
needs  for  its  own,  perhaps  unique,  purposes,  and  to  reject  w^hat  it  has  no 
use  for.  This  selective  capacity  of  bioplasm  is  everywhere  conspicuous, 
and  forms  one  of  the  most  marked  characteristics  of  the  living  substance. 
A  less  specialized  selection  of  nutritious  material  is  made  by  the  absorp- 
tive mechanism  of  the  gut,  and  this  determines  what  shall  enter  the  cir- 
culation. A  still  more  general  choice  is  made  by  the  digestive  enzymes, 
and  they  determine,  prol)ably  ionically,  what  things  shall  and  what  shall 
not  gain  access  to  the  absorptive  selecting  cells.  The  most  general 
selecting  agent  of  all  is  the  will  of  the  individual  at  large,  and  his  choice 
of  food  is  guided  by  convenience  and  by  his  intelligence  plus  his  appetite, 
and  bids  him  eat  what  is  good  for  him  by  general  consent.  He  learns, 
unconsciously  perhaps,  that  in  order  to  live  he  must  eat  proteid,  fat, 
carliohydrate,  salts,  and  water,  each  and  all,  and  that  the  proportions  of 
these  and  their  total  amount  must  both  be  approximately  right.  Further 
than  this,  the  individual  makes  no  selection  other  than  that  which  his 
appetite's  caprice  or  habit  may  command.     He  leaves  it  to  the  delicately 


154 


FOODS 


elaborated  organs  within  him  to  do  that  careful  and  complicated  select- 
ing which  he  could  not  do  otherwise  than  through  them  if  he  would. 
The  day  has  long  gone  by,  for  example,  when  physiology  could  say  to  a 
brainworker,  "  Eat  more  fish  than  muscle -workers  eat,  for  fish  contains 
phosphorus,  which  your  brain,  consuming  phosphorus,  needs."  Science 
today  would  say,  rather,  "If  the  brain  needs  phosphorus,  you  may  be 
sure  that  the  brain-bioplasm  knows  how  to  absorb  it  from  the  general 
store  of  food  circulating  so  rapidly  and  constantly  through  it."  And  this 
is  the  principle  all  through  the  average  conditions  of  average  animals. 
Voluntary  selection  of  foods  extends  only  to  the  right  quantity  of  a  mix- 
ture of  proteids,  fats,  carbohydrates,  salts,  and  water  suitably  prepared 
for  being  eaten.    Trained  protoplasm  automatically  does  the  rest. 

There  are,  however,  at  least  five  conditions  common  to  animals  which 
do  require  more  or  less  qvalitafive  adaptation  of  diet  to  their  respective 
needs.  These  conditions  are  infancy,  pregnancy  and  lactation,  senility, 
idiosyncrasy,  and  a  few  special  forms  of  disease.  Three  of  these,  the 
first  three,  are  physiological,  one,  the  last,  pathological,  and  the  other  is 
as  yet  undetermined,  whether  normal  or  abnormal.  Let  us  consider  these 
in  turn,  so  far  as  their  discussion  properly  forms  a  part  of  a  general 
treatise  on  physiology.  The  last  condition,  disease,  however,  is  largely 
outside  our  present  province. 

Infancy. — The  feeding  of  infants  is  a  matter  which  only  in  very  recent 
years  is  beginning  to  receive  the  careful  attention  it  deserves.  Few  sub- 
jects are  more  vital  to  society.  In  America  and  Europe,  on  the  average, 
nearly  one-third  of  all  children  born  die  before  before  they  are  five  years 
old,  and  largely  from  disease  more  or  less  dependent  on  improper  or 
inadequate  food.  The  infant  during  the  first  seven  or  eight  months  of 
its  extra-uterine  life  needs  nothing  but  milk.  The  comparative  compo- 
sitions of  ten  kinds  of  milk  are  given  in  this  table: 

Percental  Compositions  of  Various  Sorts  op  Milk  (Konig). 


Proteids. 

Carbo- 

Fats. 
3.8 

hydrates 
(milk- 
sugar). 

6.2  ~ 

Mineral 
matters. 

0.3 

Kinds  of  Milk. 

Casein. 

Albumins. 
1.3 

Total 
proteids. 

2.3 

Water. 

Woman     . 

1.0 

87.4 

Cow     .... 

3.0 

0.5 

3.5 

3.7 

4.9 

0.7 

87.2 

Goat    .... 

3.2 

1.1 

4.3 

4.8 

4.4 

0.8 

85.7 

Ass       .... 

0.7 

l.f) 

2.3 

1.6 

6.0 

0.5 

89.6 

Mare    .... 

1.2 

0.1 

1.3 

1.2 

5.7 

0.3 

91.5 

Ewe     .... 

5.0 

l.o 

6.5 

6.9 

4.9 

0.9 

80.8 

Buffalo      .      .      . 

5.8 

0.3 

6.1 

7.5 

4.1 

0.9 

81.4 

Llama 

3.0 

0.9 

3.9 

3.2 

5.6 

0.8 

86.5 

Dog     ...      . 

6.1 

5.1 

11.2 

9.6 

3.1 

0.7 

75.4 

Cat      ... 

3.1 

6.0 

9.1 

3.3 

4.9 

0.6 

82.1 

Human  milk  contains  2.3  per  cent,  of  proteid,  3.8  per  cent,  of  fat,  and 
6.2  per  cent,  of  carljohydrate,  almost  wholly  lactose  or  milk-sugar,  while 
cow.s'  milk  has  about  3.5  per  cent,  proteid  3.7  per  cent,  fat,  and  only  4.9 
per  cent,  sugar.  The  inorganic  salts  and  water  are  practically  the  same 
in  both.     When  necessity  compels  an  infant  to  be  "brought  up  on  the 


THE  GENERAL  NATURE  OF  DIET  155 

bottle,"  that  is,  fed  with  cows'  milk,  usually,  instead  of  its  mother's 
milk,  the  former  should  he  modified  so  as  to  more  closely  resemble  human 
milk.  As  seen  from  the  above  figures,  cows'  milk  has  almost  50  per  cent, 
more  proteid  (largely  in  caseinogen)  than  woman's  milk  has.  To  reduce 
this  proportion  water  is  added,  at  first  considerable  of  it.  The  propor- 
tion of  water  is  gradually  decreased,  month  by  month.  The  caseinogen  of 
cows'  milk  coagulates  in  the  child's  stomach  in  small  lumps,  while  that 
of  human  milk  solidifies  in  a  flocculent  mass  easily  permeated  by  the 
digestive  enzymes;  this  is  a  reason  other  than  the  proteid  disproportion 
why  cows'  milk  used  by  infants  needs  diluting  with  water.  To  compen- 
sate for  the  proportional  reduction  of  fat  by  this  dilution,  cream  is  added. 
To  make  up  the  deficiency  of  the  cows'  milk  in  the  carbohydrate,  lactose, 
(milk-sugar)  is  added,  or  even  cane-sugar.  To  insure  its  alkalinity 
usually  a  small  proportion  of  lime-water  is  used — a  saturated  aqueous 
solution  of  calcic  hydrate.  Provided  it  is  fresh  and  free  of  disease  germs, 
warmed  cows'  milk  so  prepared  (the  proportions  varying  mth  the  child's 

Fig.  75 

°  o<H.»  •  ,  o  g  0(^0  O     A^J'.\d^\CX<^  o  o 


o9o;oo.-°o°oo. 


^      ^  °o         O' 

ilk  after  standing  in  a  warm  room  fo 

Many  forms  of  bacteria  are  to  be  seen.      (Moore.) 


Pure  milk  and  milk  after  standing  in  a  warm  room  for  a  few  hours  in  a  dirty  dish. 


age)  is  a  very  good  imitation  of  woman's  milk.  To  insure  that  it  is  free 
of  the  germs  of  disease  (tuberculosis  especially,  diphtheria,  scarlatina, 
t}^hoid,  etc.),  it  is  at  present  customary  and  necessary  to  pasteurize  all 
milk  bought  in  the  open  market  by  heating  it  in  a  steam  bath  to  75°  C. 
(167°  F.)  for  a  few  minutes.  To  insure  average  composition  it  is  better 
to  have  mixed  milk  rather  than  that  from  a  single  cow.  Milk  sterilized 
by  boiling  is  rather  indigestible  (some  of  the  digestive  enzymes  contained 
being  thus  destroyed) ;  but  it  will  keep  in  a  cool  place  thus  prepared  for  a 
WTek  or  over,  and  is,  therefore,  at  times  a  great  convenience,  for  example, 
in  necessary  travelling. 

Rotch  recommends  the  following  percentages  for  the  composition  of 
cows'  milk  modified  to  suit  various  ages.  It  will  be  observed  that  the 
proportion  of  each  of  the  chief  proximate  principles  of  the  prepared  food 
is  less  at  first  than  in  average  human  milk : 


156 


FOODS 


Composition  of  Cows'  Milk  Modified  for  Various  Ages  (Rotch). 

Percentages. 


Age. 

Proteid. 

Fat. 

Sugar. 

Mineral 
matter. 

Reaction. 

1  to    2  weeks 

0.75 

2.0 

5.0 

At  least  0.15 

Always 

2to    3      " 

1.00 

2.5 

6.0 

alkaline. 

3  to    4      " 

1.00 

3.0 

6.0 

" 

4  to    6      "          .      . 

1.00 

3.5 

6.5 

(( 

6to    8      " 

1.50 

3.5 

6.5 

(( 

2  to    5  months  . 

1.50 

4.0 

7.0 

<( 

4  to    S       "         .      . 

2.00 

4.0 

7.0 

(( 

8  to    9       "       ,  .      . 

2.50 

4.0 

7.0 

(( 

9  to  10       "         .      . 

3.00 

4.0 

7.0 

11 

10  to  10.5    "         .      . 

3.25 

4.0 

5.0 

11 

10.5  to  11    " 

3.50 

4.0 

4.5 

" 

11  to  11.5    "         .      . 

unmodified. 

The  milk  of  the  ass,  common  in  some  Oriental  lands,  is  very  similar 
to  human  milk  save  in  its  small  proportion  of  fat. 

In  general,  milk  is  an  opaque,  bluish-white  or  yellowish-white  liquid, 
of  a  specific  gravity  of  from  1027  to  1035,  the  larger  the  quantity  of 
cream  the  lower,  of  course,  being  the  density  of  the  milk.  It  is  the  most 
perfect  emulsion  known,  consisting  of  a  plasma  holding  in  permanent 
suspension  innumerable  globules  of  fat  (butter),  each  from  2  to  5  mmm. 
in  diameter.  The  'plasma,  easily  separated  from  the  oil  by  dialysis,  is  a 
somewhat  opalescent,  transparent  fluid.  It  contains  as  proteids  caseino- 
gen,  lactalbumin,  an  albumose-like  substance  (sometimes  called  lacto- 
protein),  some  nuclein,  and  (in  human  milk)  a  small  amount  of  a  diastatic 
enzvme,  referred  to  above.  The  caseinogen  is  allied  to  the  alkali  albu- 
mins, and  contains  iron ;  it  does  not  coagulate  on  heating  unless  the  milk 
becomes  acid ;  it  seems  to  act  as  the  emulsifying  agent  of  the  milk.  The 
plasma  also  contains  lactose,  lecithin,  cholesterin,  traces  of  lactic  acid 
(from  the  natural  fermentation  of  the  lactose),  and  of  kreatinin  and 
urea,  besides  the  important  salts,  calcium,  magnesium,  sodium,  and 
pota.ssium  phosphates,  chlorides,  .sulphates,  and  carbonates,  with  traces  of 
iron,  fluorine,  silicon,  oxygen,  nitrogen,  and  carbonic  dioxide.  Of  these, 
calcium  phosphate  is  the  most  abundant.  The  newborn  body  being  very 
rich  in  iron,  the  milk  contains  little,  .so  little  in  fact,  as  Bunge  has  pointed 
out,  that  infants  weaned  too  late  are  apt  to  sufl'er  from  anemia  due  to  lack 
of  this  iron.  The  cream  or  fat  of  milk  consists  of  the  triglycerides  of 
palmitic,  stearic,  and  oleic  acids,  together  with  small  quantities  of  butyric 
acid  (giving  butter  its  flavor),  and  of  others  in  still  smaller  traces,  such  as 
caproic,  myristic,  and  formic  acids.  Olein  is  most  abundant  (about 
three-sevenths)  and  plamitin  next  (about  one-third),  while  the  stearin  is 
present  in  the  proportion  of  about  one-sixth;  these  are  all  about  as 
in  bo<ly-fat.  A  pigment,  lipochrome,  gives  butter  its  characteristic 
yellowness. 

Colostrum  is  the  first  milk  secreted  during  and  for  a  few  davs  follow- 
ing parturition.  The  mammary  acini  have  then  Ijeen  rapidly  prolifer- 
ating, and  it  is  natural  that  the  first  milk  produced  should  be  loaded 


THE  GENERAL  NATURE  OF  DIET  157 

more  or  less  with  the  debris  of  this  activity.  Besides  this,  the  so-called 
"colostrum-corpuscles"  may  be  seen  under  the  microscope;  these  con- 
sist of  modified  leukocytes  or  perhaps  of  milk-cells,  with  the  butter- 
droplets  to  be  seen  within  them.  Perfect  leukocytes  also  are  sometimes 
found.  The  chemical  composition  is  diiierent  from  that  of  the  milk 
coming  later,  colostrum  containing  much  more  lactalbumin  and  more  of 
a  material  often  described  as  a  globulin,  the  "  lactoprotein"  or  lacto- 
globulin  mentioned  above.  The  colostrum  is  said  to  act  as  a  purgative 
partly  in  the  newborn  child,  cleansing  and  preparing  the  intestinal 
mucosa  for  its  work. 

The  coagulation  of  milk  (very  like  that  of  blood),  commonly  called 
"curdling,"  consists  in  the  formation  of  a  clot  composed  of  casein  entang- 
ling much  of  the  fat.  In  the  presence  of  salts  of  calcium,  the  enzyme 
rennin  acts  on  the  caseinogen  in  solution  in  the  milk-plasma,  splitting 
it  into  two  parts,  one,  soluble  in  the  plasma,  called  whey-proteid,  the 
other  caseinogen,  which  is  insoluble.  This  is  a  process  of  hydrolysis,  and 
occurs  only  in  the  presence  of  calcium  phosphate.  This  substance,, 
casein,  with  its  included  fat  constitutes  the  curd.  The  caseinogen  in 
solution  in  the  whole  milk  seems  to  be  a  combination  of  a  nucleoproteid 
(nuclein)  and  a  somewhat  globulin-like  proteid.  This  is  the  present 
most-accepted  theory  of  the  coagulation  of  milk,  but  not  yet  proved; 
compare  the  coagulation  of  blood. 

The  coagulating  enzyme,  rennin,  is  secreted  by  the  glands  of  the  stom- 
ach and  of  the  pancreas.  For  the  manufacture  of  cheese  an  impure 
briny  infusion  called  rennet  has  long  been  in  use,  made  from  the  fourth 
stomach  of  the  calf.  One  part  of  rennet  will  coagulate  nearly  1,000,000 
parts  of  caseinogen. 

The  souring  of  milk  consists  of  the  acid -fermentation  of  its  lactose 
from  the  influence  of  special  bacilli  which  are  present  everywhere  in  the 
air  and  in  the  large  intestine.  The  lactose,  absorbing  water,  becomes 
lactic  acid,  which  then  breaks  up  into  butyric  acifl,  carbon  dioxide,  and 
hydrogen.  This  acid  is  very  apt  to  injure  the  digestive  process,  if  not 
the  digestive  organs,  of  young  children.  Hence  the  harm  from  sour  or 
souring  milk.  The  latter,  being  in  a  state  of  active  bacterial  change,  is 
worse  than  the  former. 

It  appears  that  the  hydrolyzing  enzymes  of  the  alimentary  canal,  the 
digestive  "ferments,"  as  they  used  to  be  called,  do  not  develop  in  the 
infant  all  at  once,  nor  are  they  all  actively  strong  in  the  child  less  than 
seven  months  old.  After  that  period  the  use  of  some  solid  food  is  properlv 
begun,  although  milk  should  form  a  considerable  part  of  the  aliment  of 
the  child  the  first  five  years  at  least.  No  solid  nutrients  are  better  adapted 
to  early  use  in  the  first  year  than  lightly  boiled  eggs  and  buttered  stale 
wheat  bread.  The  yolk  of  the  eggs  is  especially  valuable,  as  it  contains 
much  iron,  and  also  fat  and  proteid  in  a  combination  perfectly  adapted 
to  the  child's  first  year  or  two.  Gradually  the  list  of  common  articles  of 
diet  is  enlarged,  great  stress  being  laid  upon  easily  digested  proteids  and 
on  ripe,  juicy,  fresh  fruits  and  well-cooked  fresh  vegetables.     These 


158  FOODS 

foods  combine  to  furnish  in  forms  easily  available  to  the  as  yet  feeble 
dio-estion  the  enero-y  and  the  tissue  demanded  by  the  growing  bones  and 
oro-ans  and  muscles.  It  is  easier  to  overdo  the  feeding  of  fats  and  of 
carbohvdrates  than  to  underdo  it,  fat  but  "flabby"  babies  being  often 
supposed  to  be  well  nourished  when  in  reality  much  less  weight  made 
up  of  firm  bones,  solid  muscles,  and  vigorous  glands  is  of  much  greater 
worth.  The  latter  part  of  the  third  year  is  early  enough  to  begin  to  give 
to  the  child  the  general  variety  of  always  easily  digested  nutrients  of  the 
adult  diet.  The  limit  of  proteid-feeding  should  be  in  its  stimulating 
effects  on  the  preponderant  nervous  system  of  the  child,  the  "beef -fed," 
wheat-fed,  and  oat-fed  boys  and  girls  being,  other  things  equal,  those 
with  the  best  bodily  start  in  life.  Sugar  should  be,  if  possible,  used  very 
sparingly,  and  in  the  form  of  candy  given  only  immediately  after  meals. 
As  a  muscle-energizer,  sugar  is  unexcelled  (page  383),  but  during  the 
first  three  or  four  years  its  use  is  apt  to  destroy  the  appetite  for  substan- 
tial foods  not  so  attractive  to  the  taste. 

Pregnancy  and  Lactation. — A  second  physiological  condition  which 
properly  demands  some  quahtative  adaptation  of  diet  is  that  of  'preg- 
nancy and  lactation.  In  this  case  the  changes  from  the  average  diet 
required  are  very  much  less  than  in  the  feeding  of  infants,  but  they  are, 
nevertheless,  of  considerable  importance. 

The  fetus  requires  for  its  nourishment  food  which  will  furnish  it  espe- 
ciallv  with  tissue,  much  kinetic  energy  not  yet  being  required.  This 
nutriment  it  gets  from  the  circulating  proteids  of  its  mother,  largely 
serum-albumin  and  serum-globulin.  The  mother  needs,  therefore,  as 
food  an  ample  supply  of  both  tissue-builders  and  energizers.  The  one 
sort  builds  up  the  fetus,  the  rapidly  growing  uterus,  mammary  glands, 
heart,  and  in  general  supplies  the  active  anabolic  functions  characteristic 
of  pregnancy.  The  other,  the  energizers  of  the  food,  are  necessary  in 
increased  amount  to  supply  the  force  the  augmented  work  of  the  organ- 
ism requires.  Proteids  of  animal  origin  supply  these  materials  better 
than  ony  other  nutrients,  supplemented  by  a  generous,  abundant  diet, 
otherwise  average  in  composition.  During  lactation  a  somewhat  similar 
excess  of  proteids  over  the  average  is  apparently  beneficial,  together 
with  a  normal  excess  of  water.  Milk  is  richest  and  most  copious  on 
an  abundant  proteid  diet,  especially  meat.  Thereby  also  is  solved  the 
problem  of  storing  iron  in  the  fetus  in  sufficient  amount  to  last  until  solid 
food  begins  to  be  taken,  for  milk  is  deficient  in  this  essential  element. 

Senility.— In  senility,  or  old  age,  the  adaptation  of  diet  qualita- 
tively is,  as  in  the  other  extreme  of  life,  largely  in  the  way  of  using 
foods  which  are  easily  digested.  I>axative  and  easily  digested  foods  are 
especially  indicated 

Idiosyncrasy. — The  term  idiosijncrasy  (from  a  very  similar  Greek 
word  meaning  peculiarity  or  temperament)  is  an  interesting  one  in 
physiology.  Little  is  known,  however,  as  to  the  causes  and  conditions 
of  these  individual  difl'crences  between  persons.  For  our  present  purpose, 
that  is  as  concerns  diet,  the  sense  of  the  term  is  expressed  very  well  by 


THE  GEXERAL  NATURE  OF  DIET  159 

the  ancient  adage,  "One  man's  meat  is  another  man's  poison."  After 
having  discounted  these  supposed  marked  differences  as  mostly  imagi- 
nary, accidental,  or  merely  as  habits  of  thinking,  whatever  the  habits' 
origin,  there  pertainly  does  remain  a  residuum  of  differences,  often 
striking,  in  the  way  in  which  various  nutrients  affect  the  organisms  of 
different  persons.  Some  persons  are  regularly  made  sick  by  clams,  others 
suffer  from  a  dermatitis  after  eating  strawberries,  tomatoes,  etc.  The 
liking  or  disliking  of  flavors,  proverbially  unaccountable,  concerns  the 
subject  little  or  not  at  all.  Chemical  and  other  differences  in  the  tissues, 
circulating  liquids,  or  digestive  processes  are  probably  at  the  bottom  of 
these  idiosyncrasies  of  diet,  but  in  detail  most  of  these  differences  are 
quite  unknown.  These  conditions  are  facts,  and  often  not  less  important 
or  more  easily  remedied  because  sometimes  partly  imaginary.  When 
fully  established  in  an  individual  they  must  be  complied  with  and  the 
diet  accommodated  to  them  qualitatively. 

Disease. — In  certain  forms  of  disease  due  to  digestive  or  metabolic 
derangement,  adaptation  of  diet  is  more  or  less  useful  or  even  cura- 
ative.  In  invalid -feeding  the  aim  is  usually  merely  to  support  the  tissues 
and  the  strength  of  the  patient.  One  employs  for  this  purpose  every 
device  for  inducing  the  individual  and  his  digestion  to  accept  and  digest  all 
the  nourishment  possible,  adapting  the  means  to  the  end. 

In  diabetes,  however,  there  are  occasional  cases  in  which  actual  cure 
can  be  accomplished  by  diet  of  a  certain  sort,  adapted  to  the  special 
need  both  in  cjuantity  and  cjuality.  The  indication  is  to  reduce  as  far 
as  practicable  or  even  possible  the  ingested  amount  of  carbohydrate,  the 
disease  being  a  serious  disturbance  consequent  on  the  abnormal  excretion 
of  sugar  in  the  urine.  ^Meats  (except  liver),  fish,  shell-fish,  and  eggs  are 
the  staples  of  the  required  diet,  cheese  and  butter  being  used  as  largely 
as  possible.  In  mild  cases,  at  least,  milk  is  permissible,  and  such  vege- 
tables as  cabbage,  lettuce,  spinach,  cucumbers,  mushrooms,  cauliflower, 
asparagus,  onions,  and  tomatoes,  while  beverages,  such  as  water,  tea,  and 
coffee,  are  unobjectionable  in  any  amount.  Nephritis,  or  Bright's  disease, 
is  another  disease  in  which  diet  is  important  more  or  less.  In  this  case  a 
diet  of  milk  alone  is  usually  prescribed,  or  one  of  milk  extended  by  bread, 
vegetables,  and  fruit.  In  tuberculosis  a  special  diet  is  sometimes  of 
extreme  importance,  the  object  being  to  maintain  the  strength.  In  this 
case  the  adaptation  of  the  diet  is  more  quantitative  than  qualitative,  the 
patient  requiring  to  eat  as  much  as  he  can  possibly  be  made  to  digest 
rather  than  to  have  any  particular  articles  of  food.  The  patient's  meals 
must  be  frequent  and  adapted  in  every  other  way  to  bring  about  the 
desired  result  of  forcing,  so  to  say,  the  nutritive  anabolism.  Rachitis, 
or  rickets,  is  a  children's  disease  characterized  by  defective  nutrition, 
especially  of  the  bones.  The  patient  needs  in  this  case  a  diet  relatively 
rich  in  fats  and  proteids,  and  more  or  less  lacking  in  carbohydrates.  The 
meats  contain  the  earthy  salts  most  desired,  and  with  the  fats  will  furnish 
the  deficient  energy  of  the  groAving  tissues.  Carbohydrates  usually  lack 
most  of  the  inorganic  salts. 


160  FOODS 

Coffee,  Tea,  Cocoa,  Alcohol,  and  Tobacco. — We  defined  a  food 
as  any  subjjtance  which  when  taken  into  an  organism  is  capable  of 
supplying  it  with  tissue  or  of  prochicing  available  energy.  Stimulants, 
on  the  other  hand,  technically  are  agencies  that  only  goad  on  the  vital 
functions.  In  practice  so-called  stimulants  partake  in  some  degree  of 
both  these  characters,  excepting  tobacco,  which  has  no  nutrient  prop- 
erties. Of  all  the  substances  of  this  general  class,  the  above  five  are 
those  that  are  in  most  general  use  over  the  world,  but  it  is  essential  to 
note  that  there  are  many  others,  of  which  opium  is  perhaps  the  most 
important.  We  shall  shortly  see  that  of  these  "stimulants,"  alcohol  is 
more  properly  a  depressant,  while  tobacco  and  alcohol  as  well  are  used 
chiefiy  because  of  their  preponderant  sedative  action  on  the  emotional 
mental  processes. 

The  importance,  good  and  evil,  of  these  five  substances  to  the  human 
race  need  not  be  described.  We  are  in  no  sense  and  in  no  degree  con- 
cerned here  with  ethics;  we  take  things  as  we  find  them,  and  for  scientific 
purposes  state  to  scientific  people  the  best  we  can  the  scientific  truth. 
We,  as  students  of  physiology,  do  not  even  stop  to  inquire  why  many 
people  (most,  with  one  substance  or  another)  so  regularly  stimulate  their 
psychophysic  organisms.  We  may  note  in  passing,  however,  that  they 
do  so,  and  we  may  be  confident  that  they  always  will  do  so  despite  the 
hysteria  which  some,  and  the  wretched  warning  facts  which  others,  lay 
Ijefore  them.  From  the  earliest  recorded  times  and  in  all  lands  man  has 
made  from  various  vegetable  materials  "stimulants"  of  one  sort  or 
another.  In  the  lapse  of  historic  time  thus  far,  say  six  thousand  years, 
mankind  shows  no  tendency  to  stop,  or  to  lessen  even,  the  stimulation  of 
his  body  and  mind  w^ith  these  and  other  products  of  natural  and  of  human 
art.     In  a  more  enlightened  age  than  ours  they  may  go  out  of  use. 

Coffee  has  }>een  in  use  as  a  stimulant  by  Europeans  about  three  cen- 
turies, having  been  introduced  a  few  years  later  than  tea.  It  is  a  decoction 
of  the  roasted  berry  of  a  shrub,  Cofi'ea  x\rabica,  indigenous  in  Brazil, 
Arabia,  and  in  many  other  parts  of  the  world.  It  contains  at  least  two 
stimulating  elements,  an  alkaloid  of  the  vegetal-l)ase  class,  called 
caffeine  (methyl-theobromin  or  trimethyl  xanthin),  identical  in  composi- 
tion with  theine,  having  a  formula  CgHjoN^Oj  +  H2O;  and  two  volatile  oils, 
caffeol  (CgHj„02)'  sovirce  of  coffee's  aroma  and  of  part  of  its  flavor.  Be- 
sides these,  the  most  important  constituent  of  coffee  is  caff'etannic  acid, 
astringent  and  inhiliitory  of  hydrolysis  in  all  parts  of  the  alimentary  canal. 
A  ]  to  .5(J(J0  solution  of  tannin  will  arrest,  for  example,  the  digestive 
action  of  ptyalin  on  starch  completely,  but  it  is  less  inhibitory  of  pancreatic 
digestion.  As  ordinarily  marie,  when  it  is  made  well,  a  cup  of  coffee 
contains  about  0.1';  gram  (2  grains)  of  caffeine  and  0.22  gram  (3.5  grains) 
of  tannic  acid,  the  amount  of  volatile  oils  present  being  de})endent  in 
general  terms  on  the  length  of  the  time  since  the  coffee-beans  were  roasted. 
The  action  of  caffeine  is  largely  on  the  nervous  system,  stimulating  it. 
The  mental  process  is  hastened  and  supported,  emuii  and  fatigue  dis- 
pelled, mental  work  seeming  almost  a  pleasure  far  beyond  the  limits 
of  unstimulated  (iidiiraiifc,  wliilc  its  f|iiality  is  correspondingly  improved. 


THE  GEXERAL   XATURE  OF  DIET  161 

One  efiect  of  this  stimulation  of  the  nerves  is  seen  probaljly  in  its  sHght 
laxative  action  on  many,  especially  "nervous"  persons.  The  peristalsis 
of  the  gut  is  hastened,  a  result  of  the  use  of  coffee  which  may,  however, 
be  due  to  the  volatile  oils  etc.,  called  collectively  coffeol,  rather  than  to  the 
alkaloid  caffeine. 

That  the  brain  is  more  or  less  functionally  altered  by  coffee  may  be 
noted  in  the  pain  in  the  head  which  many  persons  experience  when  they 
omit  for  once  their  usual  coffee  at  breakfast.  A  nervous  restlessness  and 
tremidousness  follows  the  taking  of  two  much  coffee,  the  excitement  of 
the  nervous  system  having  then  gone  beyond  its  normal  intensity.  That 
coffee  increases  metabolism  is  proved  by  the  increased  excretion  of  urea 
and  of  carbon  dioxide  during  its  use.  ^^  ood  calls  attention  to  the  fact  that 
coffee  stimulates  both  the  intellect  and  the  imagination,  while  opium, 
another  brain-stimulant  under  some  conditions,  acts  largely  to  increase 
the  latter  and  not  the  former.  Caffeine  in  large  doses  has  a  distinctly 
diuretic  action,  increasing  the  urea  to  be  excreted.  As  we  saw  above, 
caffeine  is  a  xanthin,  and  it  is  now  known  that  the  nuclei  of  cells  contain 
xanthin-like  bodies.  It  is  supposable,  therefore,  that  coffee  may  actually 
feed  the  nerve-cells  of  the  brain  as  well  as  stimulate  them.  Its  action  on 
the  heart  is  to  augment  its  force  and  frequency,  but  the  effects  on  the 
blood -pressure  are  too  complicated  in  various  conditions  to  be  stated  here. 
Children  are  especially  susceptible  to  the  action  of  caffeine  and  hence  to 
tea  and  coffee,  the  cerebral  stimulation  being  evinced  in  them  often  by 
night-terrors  and  other  harmful  causes  of  insomnia.  Over-use  of 
coffee  in  adults  leads  sometimes  to  a  depressive  neurasthenia,  which 
disappears  when  the  occasioning  substance  is  withdrawn.  Its  tendency 
to  cause  indigestion  by  checking  hydrolysis  is  known  to  all — a  slight 
attack  of  dyspepsia  accompanied  by  unpleasant  sensations  in  the  head 
altogether  knowai  commonly  as  a  "biliousness."  These  are  the  chief 
of  the  bad  results  accompanying  the  excessive  use  of  the  beverage,  the 
proper  amount  for  benefit  having  to  be  determined  h\  exery  individual 
for  himself.  It  must  not  be  forgotten  that  the  beverage  coffee  is  usually 
accompanied  by  milk  or  cream  anrl  sugar,  both  of  which  are  of  course 
highly  nutritious  substances.  The  last  of  these,  sugar,  in  particular  is 
a  supporter  of  muscular  action  and  a  banisher  of  muscular  fatigue. 
Thus,  in  practice,  for  the  great  majority  of  cases,  coffee  as  used  is  a 
distinct  addition  to  a  meal  aside  from  its  mentally  stimulating  action. 
AMiere  there  is  a  tendency  to  indigestion  both  of  these  additions  to  the 
decoction  of  the  coffee-bean  are  apt  to  l)e  harmful,  the  sugar  because  it  is 
liable  to  ferment  before  its  absorption  as  dextrose.  The  harmfulness 
of  the  milk  is  more  obscure,  but  it  is  believed  to  be  due  to  the  formation 
of  a  chemical  union  between  the  alkaloid  and  the  proteid  caseinogen, 
the  product  of  which  for  many  individuals  is  very  indigestible.  Thus, 
black  coffee  is  often  less  objectionable  and  more  useful  than  when  taken 
with  cream  and  sugar. 

Tea,  as  has  been  learned  from  our  statements  about  caffeine,  is  much 
like  coffee  in  its  physiological  action  and  effects,  but,  weight  for  weight, 
11 


162  FOODS 

it  contains  more  than  twice  as  much  l:)oth  of  caffeine  (or  theine)  and  of 
tannic  acid  as  coffee  does.  Indian  teas  contain  more  theine  and  twice 
as  much  tannin  as  do  Chinese  teas.  Ceylon  tea  is  intermediate  in  its 
strength.  Green  tea  contains  more  volatile  oils  than  black  tea  and 
more  tannic  acid,  but  somewhat  less  of  the  alkaloid.  In  the  United 
States  the  use  of  tea  is  proportionally  decreasing,  while  that  of  coffee  is 
increasing.  In  the  British  Empire,  on  the  contrary,  the  reverse  tendency 
obtains  so  that  the  one  nation  becomes  ever  more  completely  a  coft'ee- 
drinking  nation,  and  the  other  a  race  of  tea-drinkers  to  even  a  greater 
degree  than  at  present.  In  l)rewing  tea  it  is  important  that  it  be  used  very 
soon  after  its  infusion,  for  while  the  alkaloid  dissolves  into  the  hot  water 
almost  immediately ,  the  harmful  tannic  acid  dissolves  much  more  slowly. 
For  dyspeptic  reasons,  therefore,  the  habit,  so  common  in  some  tea- 
drinking  Pt  ighborhoods,  of  keeping  the  tea-pot  on  the  nob  all  dav  is 
very  per.-icious,  and  the  women  who  indulge  in  this  hardly  fail  sooner 
or  later  to  develop  nervousness  of  a  characteristic  sort  and  a  chronic 
oa~tritis  and  a  leanness  consequent  on  the  constant  interference  with  the 
action  of  their  digestive  enzymes  which  the  excessive  tannin  exerts. 

It  is  probable  that  for  most  persons  tea  is  more  harmful  than  coffee, 
while,  furthermore,  it  somewhat  lacks  that  genuine  support  of  the  nervous 
system,  almost  amounting  to  neural  nutrition,  so  frequently  observed 
in  the  case  of  coffee.  Tea  stimulates  the  brain  and  spinal  cord,  but 
oftentimes  so  to  say  in  a  more  purposeless  way.  The  effect  is  wake- 
fulness and  mental  excitement,  but  not  so  much  of  a  stimulation  of  the 
useful  aspects  of  the  mind.  Another  disadvantage  of  tea  over  coffee 
is  the  greater  danger  of  its  harmful  adulteration  and  unhygienic  manu- 
facture, as  well  as  the  greater  cost  of  a  satisfactory  quality  of  the  substance. 

The  statements  made  above  concerning  the  relations  of  coffee  to  milk 
and  sugar  apply  equally  w^ell  to  tea — if  anything,  more  emphatically, 
for  tea  contains  much  more  tannin  than  does  coffee. 

Cocoa  is  a  beverage  made  by  mixing  with  hot  water  or  milk  the  powdered 
seeds  of  the  chocolate  tree,  Theobroma  cacao  (the  former  part  of  the  name 
meaning  "food  for  the  gods").  Chocolate  is  of  a  similar  nature,  but 
usually  contains  more  of  the  fat  of  the  bean,  cocoa  butter.  The  chief 
alkaloid  of  cocoa,  theobromine  (C^HgN^Oj),  is  nearly  the  same  sub- 
stance chemically  as  caffeine  or  theine.  It  is  present  in  cocoa,  however, 
in  much  smaller  amount  than  it  is  in  coffee  or  in  tea.  Unlike  these  latter 
stimulating  substances,  dry  cocoa  contains  about  half  its  weight,  40  to 
54  per  cent.,  of  fat,  about  20  per  cent,  of  nitrogenous  matters,  in  part 
(S  per  cent.)  proteid,  and  considerable  starch;  the  alkaloids  are  ])resent 
in  proportion  of  from  1  to  2  per  cent.  Thus,  cocoa  is  not  only  stimulating, 
but  very  nourishing,  especially  when  the  sugar  and  large  proportion 
of  milk  usually  employed,  are  added.  A  good-sized  cup  of  cocoa  so 
prepared  is  worth  nearly  400  (large)  calories. 

Cocoa,  by  its  alkaloid  theobromine  and  its  small  amount  of  caffeine, 
affects  the  neuromuscular  mechanism  much  as  does  coffee,  l)ut  in  a  very 
much  less  degree.     On  the  muscles,  howevei-,  cocoa  acts  very  powerfully 


THE  GENERAL  NATURE  OF  DIET  163 

to  ward  ofY  fatigue,  proportionally  more  strongly  than  does  cofi'ee.  In 
some  persons,  in  ordinary  quantity,  the  effect  is  somnolent  rather  than 
stimulating  to  increased  wakefulness.  The  only  danger  from  an  exces- 
sive use  of  cocoa  is  that  of  indigestion,  which  comes  from  the  large  pro- 
portion of  fat  it  contains.  Many  persons  quickly  tire  of  cocoa,  unfor- 
tunately, when  they  consume  it  frequently  and  regularly.  That  this 
tendency  may  be  readily  overcome,  however,  may  be  seen  from  its  great 
and  almost  universal  use  in  France,  for  example,  where  in  concentrated 
solution  it  is  nearly  half  of  the  common  breakfast. 

Mate  and  Guaraiia  are  beverages  similar  to  these  three  used  in  South 
America  to  some  extent.  They  are  said  to  depend  for  their  stimulative 
effect  on  the  same  alkaloids  nearly  as  do  coffee,  tea,  and  cocoa,  but  in  the 
strengths  used  by  the  natives  generally  they  are  weaker.  All  stimulants 
of  this  class  are  rich  in  inorganic  salts  (especially  soluble  compounds 
of  iron,  soda,  and  potassium),  of  value  to  the  organism. 

Alcohol. — From  natural  products  as  various  as  honey,  grains,  and 
cocoa-nuts,  and  from  scores  of  others  alcoholic  beverages  have  been 
prepared  in  all  times  and  by  all  sorts  and  conditions  of  men,  by  the  most 
civilized  as  well  as  by  the  most  savage  and  depraved.  In  America  and 
Europe  at  the  present  time  the  alcoholic  beverages  are  largely  of  three 
classes — liquors,  wines,  and  beers.  The  first  are  made  by  distillation 
from  a  large  variety  of  fermented  substances  all  containing  sugar;  the 
second  from  grapes  by  fermentation;  and  the  last  by  the  brewing  of 
malted  grains.  The  proportion  of  alcohol  in  various  beverages  is  approx- 
imately as  follows:  In  absolute  alcohol,  99.5  to  100  per  cent.,  and  in  the 
alcohol  official  in  the  United  States,  94  per  cent.  In  whiskey  there  is 
from  35  to  50  per  cent,  by  weight  of  alcohol;  in  brandy,  from  25  to  55  per 
cent. ;  in  gin,  30  to  45  per  cent.;  and  in  rum,  from  25  to  45  per  cent.  Red 
wines  and  champagne  have  of  alcohol  from  9  to  12  per  cent.,  bordeaux 
being  somewhat  the  weakest,  and  burgundy  the  strongest.  White  wines 
contain  from  10  to  14  per  cent,  of  alcohol,  and  sparkling  and  sweet  wines 
about  the  same  proportion.  Of  the  fortified  ivines  wath  alcohol-content 
varying  from  16  to  23  per  cent.,  malaga  is  the  weakest  and  sherry 
the  strongest.  Ale  has  from  4  to  8  per  cent,  of  alcohol,  and  cider 
about  the  same  proportion  unless  fresh  from  the  press,  while  domestic 
(American)  beers  have  from  2  to  6  per  cent,  of  it.  Koumis  has  in 
it,  except  when  very  fresh,  about  2  per  cent,  of  alcohol,  and  kephyr 
(similar  to  koumis,  only  made  from  cows'  milk  instead  of  from  that  of  the 
mare)  has  in  it  1  per  cent,  of  alcohol.  The  popular  bitters  and  other 
■patent  medicines  are  practically  beverages  of  the  most  insidious  sort,  and 
often  contain  percentages  of  alcohol  up  to  that  of  the  strongest  alcoholic 
liquors.  The  physiological  effects  of  alcohol  for  purposes  of  descrip- 
tion may  be  divided  into  influences  on  the  neuromuscular  mechanism, 
on  the  mental  process,  on  digestion  and  nutrition  (including  metabo- 
lism and  body-heat),  and  on  the  circulation. 

On  the  nervous  system  and  the  muscular  machines  so  closely  connected 
with  it  alcohol  exerts  an  effect  all  too  familiar  to  evervbodv.     In  general 


164  FOODS 

terms  the  nervous  system  is  disturbed,  so  that  many  movements  are  at 
first  increased  for  a  short  time  and  hastened.  Afterward,  if  the  dose 
be  large  enough,  they  are  made  ataxic  or  incoordinate,  vision  double,  for 
example,  speech  "thick,"  and  the  gait  staggering,  because  the  muscles 
do  not  pull  together  in  the  proper  degree  and  sequence.  When  quantities 
of  alcohol  larger  than  this  have  been  imbibed,  an  obviously  depressive 
stuporous  sleep  may  be  caused,  deepening  perhaps  after  a  time  into  a  coma 
somewhat  like  that  of  chloroform-narcosis,  in  which  the  tendon-reflexes 
are  lost.  In  this  condition  the  muscles  have  little  of  their  normal  tone, 
but  are  relaxed,  and  death  may  follow  from  paralysis  of  the  movements 
of  respiration.  It  will  be  observed,  then,  that  the  general  trend  of  the  action 
of  alcohol  on  the  nervous  system  is  asthenic  or  depressive  and  not  excita- 
tory. Some  researchers  in  physiology,  notably  Meltzer,  maintain  that 
alcohol  has  no  proper  sthenic  or  stimulating  effects  on  any  sort  of  pro- 
toplasm, and  that  its  eft'ects  are  always  depressive  and  devitalizing. 
They  well  account  for  the  preliminary  phenomena  of  exhilaration  by 
postulating  that  at  first  and  from  small  doses  its  action  is  wholly  on  the 
delicate  repressive  or  inhibitory  centers  of  the  brain,  depressing  their  action 
and  so  removing  the  inhibitory  control  which  they  normally  exercise  over 
the  emotional  activities.  As  we  have  seen  in  our  discussion  of  brain- 
action  and  of  the  heart,  inhibition  is  a  function  of  great  but  unknown 
importance  and  extent  in  the  nervous  system,  and  more  and  more 
does  this  repressive  aspect  of  its  action  become  emphasized  in  different 
directions.  As  regards  the  action  of  alcohol,  inhibition  may  be  pre- 
eminently important;  at  present,  however,  we  can  not  be  actually  certain 
that  such  is  the  case.  The  opposed  way  of  explaining  the  action  of 
alcohol  on  the  nervous  system  is  that  the  drug  at  first  stimula'tes  and  then 
depresses  the  actual  protoplasmic  activities  in  the  nerve-cells.  How  a 
substance  can  be  supposed  to  act  in  this  double  way  it  is  hard  to  define, 
especially  when  the  two  effects  are  of  an  opposite  sort.  Numerous 
elaborate  researches  have  shown  beyond  doubt  that  w^hile  there  is  an 
initial  stimulation  of  muscular  movements  arising  from  small  doses,  the 
general  effect  on  both  muscular  accuracy  and  endurance  is  harmful 
rather  than  beneficial.  For  example,  soldiers  do  arduous,  long-continued 
labor  much  better  without  alcohol  than  with  it.  Exactly  the  same 
effect  is  observed  when  the  muscular  action  is  not  that  requiring  long 
endurance,  but  of  a  sort  necessitating  fine  adjustments.  Alcohol  removes 
the  depressive  feelings  of  fatigue  following  unusual  exertion,  and  is  often 
used  as  a  beverage  for  this  purpose.  As  Herter  points  out,  however,  the 
excessive  exertion  itself  is  harmful,  and  would  probably  not  be  undertaken 
could  the  pains  of  it  not  be  removed  by  (h-iiikiiig — alcohol  thus  inciting 
sometimes  to  an  abnormally  exhausting  mode  of  h'fc. 

On  the  mental  process  or  mind  the  effect  of  alcohol  is  stimulating  if 
it  is  so  in  any  place.  This  comes  through  its  probable  action  on  the  cells 
of  the  cortex  cerebri,  and  is  experienced  as  a  sense  of  well-being  and  of 
haj>[)iness,  of  freedom  from  care,  and  in  an  increase  in  the  workings  of 
the  imagination,  and,  in  some  individn.ils,  not  in  others,  in  an  increased 


THE  GENERAL  NATURE  OF  DIET  165 

capability  of  mental  work  for  short  j^eriods  of  time.  It  is  in  doubt, 
however,  whether  the  quality  of  this  work  is  ever  improved  by  alcohol, 
and  there  is  much  good  experimental  evidence  (as  thatby  Kraepelin)  that 
it  is  not  so  improved,  even  for  brief  periods.  For  example,  one  research, 
done  by  Rudin,  showed  that  9o  grams  ingested  by  men  unaccustomed  to 
its  use  lengthened  the  time  required  to  add  columns  of  numbers,  made 
more  difficult  and  uncertain  the  learning  of  rows  of  figures,  shortened 
reaction-time  of  some  sorts  and  lengthened  it  in  others.  The  influence 
on  the  mental  powers  lasted,  as  a  rule,  from  twelve  to  twenty-four  hours, 
but  in  one  case  forty-eight  hours.  Similar  researches  by  several  others 
interested  in  the  question  have  given  similarly  complicated  results. 
They  agree,  however,  in  the  conclusion  that  alcohol  deranges  the  neural 
and  neuromuscular  "basis"  of  mental  activities. 

Its  power  of  abolishing  the  emotional  over-stress  of  our  hurried  and 
complicated  modern  life  is  not  easily  explained.  It  is,  however,  to  accom- 
plish this  very  purpose  that  alcohol  is  most  largely  used — as  a  beverage — 
by  the  mass  of  mankind;  they  for  the  most  part  employ  it  as  a  sedative. 
Here  too,  perhaps,  it  is  a  depressive  inhibitant,  shutting  out  from  present 
experience  those  finer  cidtiu'al  restraints  represented  probably  in  the 
cortex  cerebri. 

The  action  of  alcohol  on  digestion  and  on  the  complicated  processes 
of  metabolism  was  of  late  in  certain  respects  a  vigorously,  not  to  say 
rancorously,  discussed  question.  This  discussion  is  now,  fortunately, 
nearly  closed  by  decisive  research  conducted  by  scientists  whom  all  may 
trust.  Is  or  is  not  alcohol  a  food?  Those  opposed  infallibly  and  emo- 
tionally to  even  the  therapeutic  use  of  alcohol  in  the  saving  of  life  and 
for  the  restoration  of  health,  have  bitterly  opposed  the  presumption  of 
physiological  science  that  alcohol  is  under  some  narrow  conditions  a  food, 
lest  the  drink-evil,  one  of  the  worst  the  world  knows,  be  stimulated  still 
more.  Elaborate  and  costly  work  by  the  United  States  calorimetrist, 
Atwater,  however,  and  by  others,  has  shown  conclusively  that  in  amounts 
not  over  50  or  60  cubic  centimeters  (40  grams)  in  twenty-four  hours 
ethyl  alcohol  is  oxidized  by  the  body  with  the  production  of  heat  and 
other  forms  of  energy.  Furthermore,  it  has  been  shown  that  these 
oxidative  processes  take  place  in  the  tissues,  and  not  in  the  gut  alone, 
thus  making  the  energy  liberated  available  to  the  needs  of  organism  as 
in  the  case  of  other  foods.  Hoppe-Seyler  supposes  that  alcohol  is  formed 
in  the  normal  katabolism  of  carbohydrate  in  the  tissues,  for  he  found 
traces  of  it  in  fresh  tissues  when  they  were  distilled  with  water.  Not  more 
than  1  or  2  per  cent,  of  the  alcohol  in  the  above-mentioned  daily  amount 
leaves  the  body  unburned,  in  the  urine  and  in  the  breath,  for  the  greater 
part  of  the  maximum  quantity  of  60  cubic  centimeters  (two  ounces)  is 
oxidized  to  carbon  dioxide  and  water,  the  usual  end-products  of  carbo- 
hydrate katabolism.  It  will  be  remembered  (see  page  143)  that  the 
combustion-equivalent  of  average  proteid  and  of  average  carbohydrate  is 
4.1  calories  per  gram,  and  of  average  fat  9.3  calories.  Alcohol,  having 
no  waste,  is  of  higher  calorie-value  than  the  average  carbohvdrate,  and 


166  FOODS 

has  that  of  7  calories  per  gram.     The  maximum  food-allowance  daily 
of  alcohol,  60  cubic  centimeters,  with  a  specfic  gravity  of  0.820,  weighs 
49.2  grams,  and  would  therefore  furnish  about  364.4  gross  calories  of 
energy.     But  another  element  enters  into  the  food-question  itself:  Is 
alcohol  a  fat-sparer,  a  carbohydrate-sparer,  and  a  proteid-sparer  ?     In 
other  words,  when  used  for  food  (as,  e.g.,  in  illness),  does  alcohol  furnish 
onlv  energy,  or  does  it,  as  real  foods  do,  also  save  the  wearing-away  of  the 
proximate  principles  of  the  tissues  and  thus  of  the  tissues  themselves  ?' 
If  it  does  not,  alcohol  is  of  little  use  as  a  food  in  illness,  for  it  does  not 
replace  or  save  loss   of  body-weight.     Zunz  and    Geppert  showed  in 
1887  that  alcohol  neither  increased  to  any  extent  the  consumption  of 
oxygen  nor  changed  the  excreted  amount  of  carbon  dioxide.     In  other 
words,  alcohol  in   the  amount  named  does  save  the  fats  and  carbohy- 
drates of  the  tissues  from  consumption  by  the  wear  and  tear  of  their 
living  processes,  for  the  alcohol  itself  furnished  the  energy  required  by 
the  organism,  leaving  the  tissue-fat  and  -carbohydrates  nearly  untouched. 
This  work,  repeated  and  corroborated  by  many  other  competent  men 
since,  establishes  firmly  the  fact  that  alcohol  spares  at  least  the  fat  of 
the  body-tissues  and  therefore  may  be  of  use  as  a  real  food  in  therapeutics. 
But  it  does  more  than  this  as  a  food,  for  recent  experiments,  often 
elaborate  and  painstaking  to  an  extreme  degree,  have  shown  that  feeding 
alcohol  spares  the  proteid  of  the  tissues  as  well  as  the  fat  and  carbohy- 
drates (the  latter  existing  only,  of  course,  in  comparatively  small  amount). 
This  is  now  practically  as  certain  as  it  is  that  alcohol  spares  fat;  to  open 
minds  this  important  proposition  is  proved  beyond  a  doubt.     Atwater, 
for  example,  found  that  72  grams  of  alcohol  daily  taken  by  a  man  spared 
0.2    gram    of    nitrogen    and    spared     also    one-fifth    of    the    carbon- 
excretion     in     respiration — two-thirds     as    much     nitrogen     as     was 
spared  by  an  isodynamic  (equal-calorie)  value  of  sugar,  the  latter  being 
well  known  as  a  proteid-sparer.     Ott  showed  that  in  the  fever-condition 
also,  alcohol  acts  as  well  as  sugar  as  a  proteid-sparer.     Clopatt  found 
that  for  the  first  five  days  of  a  twelve-day  period  it  caused  an  increase 
of  proteid  katabolism,  but  acted  as  a  proteid-sparer,  decreasing,  that 
is,   the  katabolism,   for  the  other  seven   days.     Again,  Neumann,  in 
elaborate    measurements    proved    beyond    a    doubt    that   in   doses  of 
from    50   to   100  grams    daily,    it  caused    a   noteworthy  decrease    in 
proteid    katabolism,    although    not    acting    in    quite    the   same    way 
as   fat  in   this   respect.     To  have  proved    this   sparing   of  proteid  is 
even  more  important  than  to  have  shown  it  a  fat-sparer,  for  while  fat 
serves  as  a  more  or  less  dead  and  inactive  store  of  material  from  which 
at  need  energy  could  be  pnxluced,  the  proteid  of  the  body  is  all  active 
and  as  such  of  vital  importance  to  the  organism  either  as  muscle-cells,, 
epithelium,  or  other  essential  organs. 

On  the  body-temperature  alcohol  exerts  in  general  a  lowering  effect, 
as  was  asserted  first  in  1848  by  Dumeril  and  Demarquay.  Wendt 
recently  showed  that  even  small  amounts  of  alcohol  at  first,  for  ten 
minutes  only,  raised  the  temperature  0.1°  or  0.2°,  followed  by  an  equal 
lowering  below  its  original  position  for  twenty  to  thirty  minutes.     When 


THE  GENERAL  NATURE  OF  DIET  167 

the  body  was  naked,  the  loss  of  heat  was  a  degree  histead  of  one-tenth 
or  one-fifth  of  a  degree.  Large  doses  decrease  the  temperature  markedly: 
as  much  as  3°  or  5°  C.  The  large  majority  of  the  persons  of  whom  we 
read  in  the  newspapers  as  being  frozen  to  death  are  alcoholics.  The 
reasons  for  this  lowering  of  body-heat  are  at  least  two:  Alcohol,  in  a 
manner  not  yet  surely  known,  causes  an  increase  in  the  diameter  of  the 
arterioles  of  the  skin  and  of  those  just  below  it,  thus  occasioning  a  large 
increment  of  the  heat-loss  by  radiation,  conduction,  and  evaporation 
from  the  body-surface.  Again,  as  we  have  seen,  alcohol  is  probably  a 
general  depressant  of  organic  function,  and  doubtless  interferes  with  the 
heat-production  of  tissue-metabolism.  The  increased  heat-production 
noted  by  Bevan  Lewis,  Wood,  etc.,  was  probably  due  to  the  combustion 
of  the  ingested  alcohol  itself,  and  not  to  any  stimulation  of  the  metabolism. 
The  reason  that  alcohol  gives  a  strong  sensation  of  increased  warmth  is 
that  the  sense-organs  providing  the  feeling  of  heat  are  situated  in  the 
skin,  which  is,  of  course,  made  actually  warmer  by  the  vasodilatation  due 
to  the  alcohol. 

On  digestion  and  its  mechanism  the  effects  of  alcohol  are  of  great 
importance,  for  here  a  great  part  of  the  evil  alcohol  occasions  is  brought 
about  if  we  include  the  liver  in  the  digestive  system  (much  of  the  harm 
done  elsewhere  being  in  the  nervous  system).  Small  amounts  of  alcohol, 
such  as  are  contained  in  a  bottle  of  koumis  or  of  weak  beer,  taken  with 
or  just  after  meals,  have  in  many  persons  little  effect  on  digestion, 
although  the  appetite  may  be  somewhat  improved  by  its  stimulation 
of  the  digestive  juices.  (When  mixed  with  milk  it  makes  the  latter 
more  rapidly  digested  and  more  quickly.)  Sooner  or  later,  however, 
the  digestive  process  is  certainly  slowed  and  somewhat  hindered  even 
by  such  minimum  amounts,  owing  probably  to  slight  interference 
with  the  productive  glands.  \Mien  a  moderate  quantity  of  a  beverage 
containing  4  or  5  per  cent,  of  alcohol  is  taken  regularly  with  meals 
the  slowing-effect  on  digestion  is  more  marked,  but  the  ingestion  of 
this  amount,  especially  in  beer,  is  soon  followed  by  metabolic  changes 
(particularly  by  an  abnormal  deposit  of  fat)  which  are  of  consequence. 
Some  persons  might  drink  for  years  daily  with  their  dinners  a  glass  of 
8  or  10  per  cent,  claret  or  other  wine  with  no  obvious  harm  either  to 
the  digestive  process  or  elsewhere.  It  is  likely,  none  the  less,  that  the 
foundation  is  being  laid  under  such  conditions  for  a  chronic  gastritis 
and  enteritis  later  on.  It  is  after  all  the  frequent  use  of  liquors  containing 
from  30  to  50  per  cent,  of  alcohol  which  causes  the  inevitably  serious 
effects  seen  in  the  severe  chronic  or  subacute  gastritis,  cirrhosis  of  the 
liver,  degenerations  in  the  nervous  system,  fatty  degenerations  in  the 
circulatory  system,  and  so  forth.  The  hospitals  show  how  very  common 
and  how  very  serious  these  poisonings  are. 

On  the  circulation  alcohol  exerts  a  generally  stimulating  effect,  in- 
creasing the  pulse-rate  and  the  latitude  of  the  vibrations  of  the  arterial 
wall  as  felt  by  the  finger  or  registered  by  the  sphygmograph.  This 
increase  may  be  due  to  the  muscular  activity  ordinarily  great  soon  after 
ingesting  alcohol.     It  is  not  always  so  caused.     Sphygmograms  made 


168  FOODS 

from  man  by  Parkes  and  Wollowicz,  and  many  since  they  worked,  show 
an  increased  suddenness  of  ventricular  systole  and  a  shortening  of  the 
pause  between  the  systoles.  Zimmerberg  showed  that  large  doses  depress 
both  the  rate  and  the  power  of  the  beat.  Whether  blood-pressure  be 
increased  or  not  depends  in  any  case  on  the  balance  between  the  aug- 
mentation of  the  pumping-action  by  the  heart  and  the  size  of  the  arterioles 
and  capillaries  through  which  the  streams  must  pass.  Sometimes, 
therefore,  the  pressure  will  be  increased,  sometimes  decreased,  sometimes, 
doubtless,  unchanged  by  the  ingestion  of  moderate  doses  of  alcohol. 
Alcohol's  harm  on  the  heart  is  brought  about  partly,  it  appears,  by  the 
shortening  of  the  rest-period  which  it  produces,  as  mentioned  above,  for 
this  soon  leads  to  hypertrophy  and  general  derangement,  since  no 
portion  of  an  organism  can  work  continuously. 

Such  are  the  chief  of  the  physiological  effects  of  alcohol  on  the  animal 
economy  as  now  understood  by  physiologists.  They  go  to  show  to  the 
student  of  medicine  that  alcohol  may  be  of  great  use  as  a  therapeutic 
agent  in  disease,  feeding  the  body,  sustaining  the  mind,  improving 
digestion,  supporting  the  heart  when  perhaps  all  that  is  necessary  for 
saving  a  life  is  this  feeding,  sustaining,  improving,  or  supporting  for  a 
brief  period  of  time.  But  these  physiological  effects  go  to  show  to  all 
men  that  alcohol,  although  a  sedative,  is  an  irritant  and  depressive  poison 
generally  inimical  to  life,  with  which  a  normal  individual  should  have, 
even  physiologically  speaking,  nothing  to  do. 

Tobacco  is  so  frequently  practically  a  part  of  a  meal,  that  it  is  not 
improper  to  consider  its  effects  briefly  in  this  place.  The  active  principle 
of  tobacco  is  an  alkaloid  nicotine,  with  the  empirical  formula  C^^Hj^Nj. 
Pictet  and  Rotschy  claim  to  have  discovered  in  tobacco  three  other 
alkaloids:  "nicotimin,"  with  composition  like  nicotine's;  "nicotein," 
(CjpHjgNj);  and  "nicotellin,"  (CjoHj^Nj).  They  find  in  ten  kilos  of 
tobacco-juice  1000  grams  of  nicotine,  20  grams  of  "nicotein,"  5  grams 
of  "nicotimin,"  and  1  gram  of  "nicotellin,"  and  announce  the  action  of 
the  nicotein  to  be  like  that  of  nicotine,  but  more  toxic.  We  shall  look 
at  the  action  of  nicotine  on  the  nervous  system,  on  the  mind,  and  on  the 
circulation. 

On  the  nervous  system  the  action  of  nicotine  is  complicated.  It  has 
the  jjeculiar  power  certainly  of  so  disturbing  the  neurones  as  to  block 
the  afferent  impulses  leaving  them.  It  also  paralyzes  the  peripheral 
motor  nerve-endings  after  a  brief  preliminary  excitation  of  them.  The 
convulsions  which  ff)llow  large  doses  of  the  alkaloid  have  been  shown 
by  Krocker  to  be  quite  independent  of  the  brain,  to  be  occasioned,  then, 
in  the  cord.  Sensory  centers  and  nerves  are  not  affected  by  nicotine. 
In  what  manner  it  affects  the  nervous  system  so  as  to  abolish  the  general 
sensation  and  pain  of  hunger,  one  of  its  conspicuous  effects,  it  is  impossible 
at  present  to  say,  possibly  by  its  peculiar  sedative  action,  as  in  case  of 
opium. 

On  the  mind  nicotine  exerts  a  strong  calming  and  quieting  effect,  while 
at  the  same  time  the  brain  is  so  stimulated  that  long-continued  mental 


THE  GENERAL  XATURE  OF  DIET  109 

labor  is  less  fatiguing.  The  same  action  is  often  noticed  as  regards 
muscular  exertion.  Tobacco  is  indeed  often  of  great  benefit  in  this 
fatigue-abolishing  way  to  hunters,  lumbermen,  soldiers,  and  others  who 
are  liable  to  be  obliged  to  undergo  long  periods  of  exertion.  This 
sedative  effect  on  the  thoughts  and  fears  and  worries  of  life  is  the  source 
of  one  of  tobacco's  benefits  to  humanity.  It  becomes,  in  these  days  of 
hurried  eating  especially,  a  conckicer  to  good  digestion  by  tending  to 
make  pleasant  a  quiet  untroubled  hour  or  half-hour  after  a  meal,  espe- 
cially as  the  stimulating  action  on  the  mind  makes  toward  sociability. 
In  having  thus  the  double  and  seemingly  almost  contradictory  efi'ects  of 
quieting  hurried  anxiety  and  yet  of  stimulating  mental  action,  tobacco 
stands  closer  to  opium  than  does  any  other  substance  known.  The  action 
differs  from  opium's,  however,  in  that  it  is  the  intellect  and  not  alone 
the  imagination  that  is  stimulated  by  tobacco,  while  the  sedative  efi'ects 
of  the  two  plants  are  very  similar,  although  that  of  opium  is  very  much 
more  powerful.  In  combination  with  coffee,  tobacco  exerts  a  very  strong 
stimulation  on  the  mind,  sleeplessness  being  a  frequent  consequence. 

The  circulation  and  especially  the  heart  is  more  strongly  and  injuriously 
influenced  by  the  frequent  taking  of  too  much  tobacco  than  any  other 
system  of  the  organism,  for  the  rhythm  of  the  heart  is  deranged  by 
its  excessive  use  and  made  irregular  both  in  the  force  and  the  time 
of  the  heart-beats.  This,  the  "tobacco-heart,"  is  the  most  common 
effect  of  excess,  but  the  results  of  its  continuance  are  not  cumulative  to 
any  considerable  extent  (as  are  those  of  alcohol  and  opium),  and  pass  off 
in  a  relatively  short  time  when  the  habit  is  broken.  The  immediate 
action  of  nicotine  on  the  heart  and  peripheral  vessels  is  not  definitely 
known,  the  large  number  of  experiments  on  various  sorts  of  animals 
being  to  our  present  understanding  contradictory. 

Both  the  power  and  the  disposition  to  do  muscular  work  are  un- 
doubtedly lessened  by  the  absorption  of  these  alkaloids — an  effect  of 
which  the  physiological  explanation  is  not  as  yet  at  hand.  It  is 
apparently  a  matter  either  of  neural  or  of  muscular  metabolism. 

On  the  mucous  membrane  of  the  mouth  and  throat  tobacco  sometimes 
exerts  an  injurious  drying-action,  leading  to  chronic  inflammation  of  a 
mild  type.  Its  nauseating  effect  is  reflexly  caused  probably  by  stimula- 
tion by  the  nicotinized  saliva  of  the  unaccustomed  nerve-endings  in  the 
stomach-wall.  Were  this  nausea  not  so  sharp  and  painful  to  the  youth- 
ful mind,  there  would  be  even  more  smokers  than  there  are.  Nicotine 
is  said  to  cause  an  increase  in  the  urinary  excretion  of  uric  acid  and  of 
phosphoric  acid;  it  does  not  affect  the  respiratory  exchange.  Excessive 
use  of  tobacco  produces  insomnia  and  great  nervous  irritability,  besides 
the  functional  cardiac  irregularity  already  noted.  Each  user  of  the  herb 
must  determine  for  his  o^^^l  particular  organism  the  limits  beyond  which 
needless  injury  is  done  him. 

To  the  evolving  and  unstable  nervous  systems  of  childhood  and  youth 
all  of  these  substances  usually  knowai  as  stimulants  are,  of  'course, 
particularly  poisonous. 


CHAPTEE    V. 

DIGESTION. 

Having  now  seen  in  outline  what  the  food  of  the  body  is  and  should 
be  like,  our  next  search  is  in  what  manner  it  becomes  made  into  tissue- 
protoplasm  which  is  alive  again.  Food,  as  we  have  seen,  is  largely  either 
animal  or  vegetable.  Substances  of  these  origins  are,  bv  definition,  forms 
of  protoplasm;  The  present  chapter,  then,  deals  with  that  portion  of  the 
reanimation  of  food  called  digestion. 

The  whole  process  by  which  food  proper  is  converted  into  tissue  or 
made  a  source  of  energy  to  the  organism  may  conveniently  be  divided 
for  purposes  of  description  into  four  stages,  wdiich  we  shall  discuss  under 
the  arbitrary  names  digestion,  absorption,  nutrition,  and  excretion.  The 
last  process,  excretion,  is  quite  as  essential  as  the  others,  for  most  of  the 
products  of  katabolism  are  of  such  a  nature  that  unless  promptly  removed, 
they  quickly  bring  about  protoplasmic  and  organic  death.  In  our  sketch 
of  protoplasm  we  have  already  seen  an  outline  of  the  general  nature  of 
this  extensive  vital  function  of  nutrition.  Here  we- extend  it  and  apply 
it  to  man.  So  great  is  the  complexity  of  animal  function,  whether  taken 
as  a  w^hole,  or  in  any  of  its  parts,  and  so  interdependent  are  its  various 
portions,  that  sometimes,  in  fact,  there  is  no  such  sharp  discrimination 
between  functions  as,  for  convenience  of  description  and  ease  of  learning, 
we  describe.  We  find  an  example  of  this  circumstance,  so  common  in 
science,  in  the  latter  limit  of  "digestion."  Arbitrarily  we  shall  leave  the 
nutritive  materials  in  this  chapter  when  they  are  all  ready  to  be  absorbed 
into  the  complex  circulation  of  the  blood  and  lymph.  It  is  the  work  of 
digestion  proper  to  prepare  the  food  for  absorption.  When,  however,  one 
considers  that  part  of  the  work  of  digestion  is  apparently  done  as  the 
nutritive  substances  pass  through  the  thin  wall  of  the  intestine,  and  that 
in  the  villi  both  processes  may  take  place,  it  is  clear  tiiat  the  two  subjects 
are  much  less  sharply  discriminated  by  the  organism  than  by  the  ana- 
lyzing mind  describing  them.  This  general  interdependence  of  organic 
functions,  this  perfect  unification,  more  or  less  evident,  of  the  structural 
and  fimctional  multitude  making  up  the  individual,  is  an  important 
matter  for  anyone  to  remember  who  would  understand  man  in  any  way 
adequately.  Only  so,  indeed,  will  his  view  be  broad  enough  and  accurate 
enough  to  rightly  interpret  things.  We  encounter  repeatedly  reminders 
of  this  principle  that  description  implies  a  misleading  separateness  in 
structure  and  function  when  in  reality  the  process  is  often  a  greatly 
involvcHJ  continuity. 

As  was  seen  to  be  the  case  with  the  function  of  respiration,  digestion  is 


DIGESTION 


171 


basally  a  necessary  process  of  protoplasm  either  directly  or  indirectly, 
and  hence  is  universal  in  the  animal  kingdom.  It  is,  moreover,  a,  process 
common  enough,  even  as  animals  perform  it,  in  the  vegetable  kingdom. 


Fig.  76 


D/G£6T/0// 
^  Protein 
O  /l/bumin 
O  6tarch 
®  Sugar 
®  Fdts 
®  Coagulated  ca^einogen 


172 


DIGESTION 


Thus,  the  Venus'  flytrap  (Dionea),  native  to  North  Carolina,  has  an 
elaborate  sensori-motor  mechanism  for  catching  its  insect-prey  and  the 
essentials  of  a  digestive  apparatus  for  preparing  it  for  absorption  into 
the  vital  juices  of  the  plant.  The  fly-catcher  (Drosophyllum)  of  Morocco 
and  Portugal  and  the  pitcher-plant  so  common  in  New  England  bogs, 
catch  insects  which  crawl  into  them  in  search  of  honey  or  of  water  by 
means  of  glandular  hair-like  organs  that  secrete  a  fluid  at  once  viscid  and 

digestive,  and  make  good  nutritional 
Fig.  77  usc  of  them.     Tliesc  are  but  exam- 

ples of  plants  which  have  a  true 
digestion  by  means  of  chemical- 
enzymes  (hydrolyzing  agents),  while 
there  are  many  others  which  in  one 
way  or  another  catch  and  hold  living 
animals  and  other  sorts  of  food  and 
absorb  the  nutritive  liquids  from 
them  either  at  once  or  as  they  decay. 
All  plants  are  able  to  absorb  pre- 
pared carbohydrate  and  proteid 
food-substances,  but  there  are  many 
genera  that  also  digest  them. 

The  Human  Digestive  Mechanism. 
— A  knowledge  of' the  anatomy  and 
histology  of  the  human  digestive 
apparatus  is  obviously  a  prerequisite 
of  an  understanding  of  the  diges- 
tion as  a  process.  This  information 
text-books  other  than  those  of  Phy- 
siology fully  supply,  and  to  them 
the  reader  is  earnestly  referred. 

The  mouth  or  oral  cavity  is  the  re- 
ceptacle into  which  the  food  is  placed 
by  the  hands  and  the  lips,  and  where 
it  is  masticated  and  insalivated.  The 
tongue  is  an  important  organ  of 
digestion,  for  by  it  almost  alone  the 
food  is  placed  and  kept  between  the 
two  sets  of  teeth  during  its  masti- 
cation. It  is  one  of  the  most  versa- 
tile organs  of  the  body  in  that  it  has  not  only  important  motor  functions, 
but  because  it  bears  also  the  end-organs  of  the  sense  of  taste  of  so  great 
importance  in  digestion. 

The  salivary  glands  empty  their  product  into  the  mouth-cavity.  Each 
of  them  produces  to  a  certain  minor  extent  mixed  saliva,  although  for  the 
most  part  the  product  of  each  is  characteristic.  The  parotid  gland  is 
the  largest  of  them,  and  weighs  from  15  to  30  gm.  This  gland  pours 
its  saliva  into  the  mouth  through  Stenson's  duct,  which  is  about  6  cm. 


Alimentary  tract  of  the  frog  seen  from  in 
■front:  Mh,  mouth;  Z,  extended  tongue;  S, 
opening  into  the  larynx,  showing  the  glottis; 
Oe,  esophagus;  M,  stomach;  D,  small  gut; 
P,  pancreas;  L,  liver;  G,  gall-bladder;  Dc, 
common  place  of  emptying  of  the  liver  and 
pancreas  into  the  gut;  R,  large  gut;  lib, 
urinary  bladder;  CI,  cloaca;  A,  anus. 
(Claus.) 


DIGESTION 


173 


long  and  enters  that  cavity  behind  the  second  upper  molar  tooth 
The  sahva  secreted  by  this  gland  is  largely  of  a  serous  variety,  that 
is,  it  is   thin,   albuminous,  and  highly  lubricating.     The  submaxillary 


Fig.  78 


Fig.  79 


The  stomachs  of  four  sorts  of  birds:  A,  pelican;  B,  tanager;  C,  hawk;  D,  ostrich;  oe,  esoph- 
agus; dm,  chemical  stomach;  r,  constrictor  muscle;  m,  under  part  of  stomach  (reservoir);  pm, 
antrum  pylori.      (Haller.) 

gland,  weighing  about  S  gm.,  sends  its  product  into  the  mouth  by 
Wharton's  duct,  which  ends  on  both  sides  of  the  frenum  linguae.  The 
sublingual  gland  opens  by  numerous  small  ducts  (those  of  Rivini,  from 
ten  to  twenty  in  number),  directly 
into  the  mouth  in  various  places. 
Besides  these  three  major  glands 
there  are  numerous  others  situated 
about  the  mouth-cavity.  The  pro- 
duct of  these  glands  is  largely  of  a 
mucous  sort,  whereas  the  submax- 
illary gland  secretes  both  kinds  of 
saliva  in  nearly  equal  proportions. 

^Nlixed  saliva  as  it  pervades  the 
walls  of  the  mouth  is  an  opalescent, 
somewhat  glairy  liquid,  tasteless, 
and  with  a  specific  gravity  of  about 
1005.  Its  chemical  reaction  is  nor- 
mally alkaline;  but  when  not,  the 
acidity  is  due  to  fermentation  of  bits  of  food  in  the  mouth.  In  addition 
to  the  organic  constituents  of  saliva  (mucin,  alkali-albumin,  a  globulin, 
serum-albumin,  and  ptyalin,  which  is  the  proper  enzyme  of  saliva),  this 


The  nerve-endings  in  the  salivary  glands: 
I,  I,  section  in  a  column  of  cells;  H,  demi- 
lune-cell;  n,  n,  nerve-fibers.      (Retzius.) 


174 


DIGESTION 


fluid  contains  several  inorganic  salts,  notably  potassium  sulphocyanate. 
The  quantity  of  saliva  secreted  in  twenty-four  hours  in  health  appears  to 


Fig.  80 


3Iolnn 


Canine 


Section  of  salivary  gland:  a,  alveolus;  b,  connective  tissue  which  will  be  seen  to  penetrate 
the  gland  di\ading  it  into  lobes;  c,  points  to  the  center  of  a  lobe;  d,  septum  between  lobes; 
e,  gland  duct  lined  by  columnar  epithelium.      (Bates.) 

be  rather  more  than  a  liter,  the  variation  being  large.    Probably  the  three 
large  glands,  parotid,  submaxillary,  and  sublingual,  secrete  the  saliva 

into  the  mouth  only  during  masti- 
FiG.  81  cation.      The  other  glands    (the 

buccal,  labial,  lingual,  and  molar) 
are  relied  upon  to  keep  the  mouth, 
pharynx,  and  tongue  moist,  a  con- 
dition necessary  to  mucous  mem- 
branes. 

The  teeth  are  the  organs  by 
which  the  food  that  is  in  need  of 
it  is  cut  and  ground  into  fine 
pieces,  or  a  paste,  preparatory 
to  being  swallowed  and  digested 
farther  on  in  the  alimentary 
canal.  They  are  developed  in 
two  sets.  C)n  rare  occasions  a 
third  set  may  be  started. 

The.  temporary  set  consists  of 
twenty  teeth,  half  of  them  in 
each  jaw.  Beginning  in  the  mid- 
dle line  on  either  side  of  each  jaw 
are  two  incisors,  one  canine,  and 
two  molars.  These  break  through  the  gums  nearly  in  pairs  at  in- 
tervals between  the  end  of  the  first  half-year  after  birth  and  the  begin- 


The  temporarj'  teeth.  The  numbers  denote 
the  respective  times  of  their  eruption  in  months. 
(Hall.) 


DIGESTION 


175 


ning  of  the  third  year.  The  order  of  their  eruption,  the  periods,  on 
the  average,  at  which  they  come  into  view,  is  as  follows:  The  lower  cen- 
tral incisors  appear  at  seven  months,  and  the  upper  central  incisors  a 
little  afterward;  the  upper  lateral  incisors  show  at  nine  months,  and  the 
lower  lateral  incisors  somewhat  later;  the  first  molars  in  both  jaws  about 
the  twelfth  month;  the  canines  at  about  the  eighteenth  month;  and  the 
second  (that  is,  the  posterior)  molars  at  about  the  twenty-fourth 
month.  The  temporary  teeth  are  similar  in  general  shape  to  the 
permanent  teeth,  but  are  much  smaller,  bluer  in  tinge,  and  less  firmly 
implanted. 

The  permanent  set  of  teeth  begin  to  displace  the  temporary  teeth  during 
the  sixth  or  seventh  year,  although  the  sacs  of  all  the  permanent  teeth,  as 
well  as  those  of  the  temporary  set,  are  present  in  the  jaw  at  birth.    At  the 


Fig.  82 


Molars 


Bicuspids 


Canine 


The  permanent  teetli. 


The  numbers  denote  the  respective  times  of  their  eruption  in  years, 
(Hall.) 


sixth  year,  therefore,  the  jaw  contains  forty-eight  teeth — the  whole  of 
the  deciduous  set  and  all  the  permanent  teeth  except  the  third  molars 
("wisdom  teeth").  The  twenty  teeth  of  the  temporary  set  are  replaced 
by  a  like  number  of  somewhat  similar  permanent  teeth,  and  these  have 
similar  names  save  that  those  replacing  the  temporary  molar  teeth  are 
called  bicuspids  and  have  each  two  cusps  instead  of  the  molar's  three. 
In  addition  three  molars  are  added  posteriorly  on  each  side  of  each  jaw, 
making  the  permanent  teeth  thirty-two  in  number.  The  first  of  the  true 
molars  (that  is,  that  nearest  the  middle  fine),  the  earliest  of  the  permanent 
teeth,  appears  at  about  the  end  of  the  sixth  year,  then  the  central  incisors 
at  seven  years,  the  lateral  incisors  at  eight  years,  the  first  bicuspids  at 
nine  years,  the  second  bicuspids  at  ten  years,  the  first  canines  at  eleven 
years,  the  second  canines  at  twelve  years,  the  second'  molars  between  the 
twelfth  and  thirteenth  vears,  and  the  unreliable  third  molars,  or  wisdom 


176 


DIGESTION 


teeth,  only  at  a  very  variable  time  ranging  from  the  seventeenth  to  the 
twenty-fifth  year. 

Mastication. — This  is  the  first  of  the  digestive  processes  if  we 
neglect  prehension  of  the  food  by  the  hands  and  lips.  It  is  an  habitual 
voluntary  process  carried  on  by  a  neuro-muscular  mechanism,  and  once 
started  goes  on  almost  reflexly. 

The  masticatory  muscles  may  be  considered  briefly  in  the  following 
classes:     Those  which  raise  the  lower  jaw,  those  which  move  it  laterally 

Fig.  83 


im:\^l% 


The  teeth  of  a  seven-year-old  child.      The  permanent  teeth  are  already  funned,  and  are 
waiting  for  positions  in  the  jaws.      (Litch.) 

and  forward,  those  which  lower  it,  and  those  which  keep  the  food  in 
place  between  the  opposed  sets  of  teeth.  (1)  The  elevators  of  the  lower 
jaw  are  the  masseter,  the  temporal,  and  the  internal  pterygoid.  The 
mas.seter  connects  the  molar  process  and  the  zygoma  with  the  angle  and 
ramus  and  coronoid  process  of  the  jaw  with  powerful  contractile  fibers, 
its  action  being,  therefore,  to  draw  the  jaw  both  forward  and  backward 
as  well  as  upward  on  the  upper  maxilla.  The  temporal  muscle  fills  com- 
pletely the  temporal  fossa  of  the  skull  and  its  fibers  converge  thence  to 
the  coronoid  process  of  the  jaw.  By  its  contraction  the  latter  is  drawn 
powerfully  uj)ward,  wliilc  at  the  same  time  tlic  movement  is  somewhat 


DIGESTION  177 

backward  to  help  the  grinding  motions  of  the  teeth  ancl  to  keep  the 
maxilla  in  its  socket.  The  internal  pterygoid  muscle  is  in  shape  and 
direction  much  like  the  masseter,  and  acts  to  strongly  press  the  lower 
jaw  almost  directly  upward  against  the  upper.  Tlie  inferior  maxil- 
lary nerve  supplies  these  three  muscles.  These  three  muscles  combined 
exert  a  pressure  of  several  kilos  as  the  crushing  power  of  the  molar  teeth. 
(2)  The  lateral  mover  of  the  inferior  maxilla  is  the  external  pterygoid 
muscle,  whose  powerful  fibers  pass  horizontally  backward  and  outward 
to  the  condvle  of  the  iaw.  When  the  muscle  of  the  rig-ht  side  contracts 
the  jaw  is  moved  toward  the  left,  and  vice  versa.  Owing  to  the  presence 
of  the  fibers  which  pass  backward,  when  both  external  pterygoids  con- 
tract together  the  jaw  is  drawn  forward.  This  muscle  also  is  supplied 
by  the  inferior  maxillary  branch  of  the  fifth  nerve.  (3)  The  muscles 
which  lower  the  jaw  are  the  digastric,  the  mylo-hyoid,  the  genio-hyoid, 
and  the  platysma,  of  which  the  first  two  are  the  more  important,  while 
gravity  is  a  force  which  in  the  mastication  of  ordinary  food  aids  in  the 
descent  of  the  jaw. 

The  digastric  muscle  has  tw^o  distinct  bellies,  the  anterior  and  posterior, 
and  only  the  latter  has  action  in  depressing  the  jaw.  This  anterior  belly 
extends  from  the  hyoid  bone  upward  and  forward  to  the  inner  surface 
of  the  lower  jaw  near  the  median-line.  It  is  supplied  by  the  inferior 
dental  branch  of  the  fifth  nerve.  The  mylo-hyoicl  muscle  is  a  flatter 
muscle  than  the  preceding,  and  is  placed  just  inside  it,  forming  the  mus- 
cular floor  of  the  mouth.  It  extends  between  the  hyoid  bone  and  the 
mylo-hyoid  ridge  of  the  inferior  maxilla.  The  inferior  dental  nerve 
supplies  this  muscle  also.  The  genio-hyoid  muscle  is  a  slender  bundle  of 
fibers  extending  between  the  symphysis  of  the  jaw  and  the  mitldle  por- 
tion of  the  hyoid  bone.  This  muscle  is  supplied  by  the  twelfth  or  hvpo- 
glossal  nerve.  AYhen  the  hyoid  bone  is  fixed  from  below  by  tonic  con- 
traction of  the  sterno-hvoid  and  other  muscles,  contraction  of  these 
three  muscles  depresses  the  jaw  with  considerable  force.  The  platvsma 
myoides  muscle  is  a  thin  and  superficial  muscular  fabric  extending  from 
the  clavicle  and  acromion  and  superficial  fascia  of  the  upper  part  of  the 
thorax  to  the  whole  length  of  the  body  of  the  jaw.  Its  contraction  tends 
to  depress  the  jaw. 

^lastication  employs  these  muscles,  the  tongue,  and  the  muscles 
of  the  cheeks,  these  last  being  the  active  agents  in  keeping  the  food 
between  the  cutting  and  grinding  teeth.  In  man  the  masticatory 
movements  are  largely  vertical,  the  antero-posterior  motion  being  slight, 
as  are  also  the  lateral  movements  of  the  jaw.  As  has  been  noted  from 
our  rehearsal  of  the  actions  of  the  various  muscles,  a  large  variety  of 
jaw-movements  are  possible  through  the  simultaneous  operation  of  more 
than  one  muscle  each  with  a  difi'erent  eft'ect  on  the  jaw.  By  this  means, 
on  a  principle  universal  almost  in  muscular  coordination,  all  the  oblique 
motions  of  the  jaw  are  to  be  observed  during  vigorous  mastication  unre- 
strainetl  by  the  inhibiting  conventionalities  of  culture.  The  tongue  is  at 
once  the  master  and  the  servant  of  the  mouth,  and  pervades  it  on 
12 


178  DIGESTION 

occasion  in  nearly  every  part.  In  mastication  its  office  is  to  gather  up 
the  portions  of  the  food  being  chewed  and  to  keep  them  sufficiently  long 
l)etween  the  teeth  for  complete  mastication. 

This  directing,  guiding,  and  restraining  function  of  the  versatile  tongue 
would  be  impossible  of  its  accomplishment,  even  with  the  muscles  of  the 
cheeks  to  aid,  were  it  not  for  the  saliva,  with  its  sticky  mucin,  to  fasten 
the  crumbs  together.  The  saliva  is  poured  out  into  all  portions  of  the 
mouth  in  a  certain  amount,  but  principally  where  it  will  be  most  useful 
to  the  grinding  mechanism,  behind  the  molar  teeth,  under  the  tongue, 
and  on  the  floor  of  the  mouth.  Besides  reducing  the  bite  of  food  to  a 
mass  of  fine  particles  easy  of  access  by  the  digestive  juices,  mastication 
serves  to  mix  thoroughly  the  bolus  of  food  with  this  important  amylo- 
lytic  and  alkaline  digestant. 

The  saUva  is,  then,  an  essential  substance.  It  has  the  power  of  chemi- 
cally dissolving  an  important  order  of  foodstuffs,  and  it  alone  makes 
possible  adequate  mastication  and  deglutition  (passage  of  the  food  into 
the  stomach  from  the  mouth).  Of  these  two  sorts  of  function,  the  former, 
chemical  solution,  is  apparently  of  the  lesser  importance,  for  saliva  in 
this  respect  has  perhaps  a  more  efficient  substitute  in  the  pancreatic  juice 
employed  farther  down  the  gut.  Without  the  mechanical  services  of 
saliva,  however,  the  swallowing  of  food  is  inconceivable,  if  not  in  liquid 
form  or  taken  with  a  large  quantity  of  liquid. 

Saliva,  then,  (a)  lubricates  the  tongue  and  keeps  the  mucosa  of  the 
mouth  in  normal  condition,  (b)  It  softens  the  food  by  its  fluidity, 
makes  it  chewable,  and  renders  it  easily  moved  about  by  the  tongue 
and  cheeks,  (c)  It  sticks  together  the  food-particles  by  its  mucin,  so  that 
a  definite  bolus  suitable  in  size  and  shape  to  be  swallowed  is  easily  made 
by  the  tongue,  (d)  It  lubricates  this  bolus  by  the  serous  element  of  its 
composition,  so  that  it  may  be  quickly  passed  into  the  esophagus  and  then 
painlessly  down  that  narrow  tube,  (e)  It  starts  at  least  the  hydrolysis 
of  starchy  carbohydrates,  (/)  It  dissolves  such  food  as  is  soluble  in  a 
faintly  alkaline  lif|uid,  and  thus  makes  possible  the  important  sense  of 
taste  (see  page  357), 

One  of  these  uses  of  the  saliva  demands  further  description — namely,  its 
solvent  or  digestive  action  on  carbohydrates.  This  eft'ect  is  brought  about 
by  a  member  of  a  class  of  bodies  as  yet  in  themselves  little  understood, 
called  enzymes,  or  ferments,  this  particular  enzyme  (probably  identical 
with  the  animal  diastase  or  amylopsin  of  the  pancreas)  being  called 
ptyalin.  AVhat  ptyalin  is,  chemically  speaking,  is  still  unknown.  It  has 
been  supposed  that  it  is  protein  in  its  composition  or  a  close  derivative  of 
a  protf  id.  Recent  researches,  however,  have  made  it  necessary  to  deny 
that  one  enzyme,  at  least,  is  proteid  substance,  for  an  eminent  chemist 
fPekelharring)  is  sure  that  he  has  removed  by  repeated  precipitation  all 
traces  of  [)roteifl  from  pepsin,  a  typical  enzyme,  ^Miatever  the  details 
of  the  actions  set  going  by  enzymes,  the  process,  reduced  to  its  simplest 
terms,  seems  to  be  one  of  hydrolysis,  "^rhis  term  means  the  absorption  of 
water  by  a  molecule  of  the  material  acted  upon  and  the  latter's  immediate 


DIGESTIOX  179 

splitting  into  simpler  substances.  These  are  found  in  practice  to  contain 
less  latent  energy  than  the  molecule  from  which  they  originated.  The 
hydrolytic  process,  then,  is  one  of  katubolisra,  the  resulting  chemical 
materials  being  more  stable  than  their  mother-substance.  That  water 
is  required  in  the  reaction  is  shown  by  the  fact  that  no  known  enzyme 
acts  save  in  its  presence. 

Various  conditions  determine  the  rate  of  digestive  zymolysis,  as  has 
in  part  already  been  seen  above.  Among  these  are  temperature  (the 
normal  body-temperature  is  the  optimum),  chemical  reaction,  fluidity  or 
solidity  of  the  substance  acted  on,  the  size  of  the  particles  of  the  latter, 
the  concentration  of  the  products  of  the  zymolysis,  the  concentration 
of  the  enzyme,  and  whether  or  not  the  food-substance  has  been  cooked 
(heated)  or  not.  The  necessity  of  promptly  removing  the  products  of 
the  hydrolysis  in  order  that  the  action  of  the  enzyme  may  continue 
Briiche  showed  in  1862;  it  is  a  fact  often  demonstrated  since.  The  im- 
possibility of  thus  removing  the  products  of  the  action  when  carried  on 
artificially  outside  a  living  body  is  one  of  the  chief  difficulties  in  experi- 
ments on  digestion  under  these  circumstances.  In  the  organism  these 
products  are  promptly  removed  by  absorption  into  the  circulation.  No 
explanation  of  this  hindrance  is  at  present  available,  but  it  is  probably 
chemical  and  dependent  on  some  sort  of  inhibiting  reaction  involving 
the  enzyme.  The  slowing  influence  exerted  by  the  excessive  heating  of 
the  food-substance  to  be  acted  upon  is  probably  a  matter  of  general  solu- 
bility; the  heating  of  starch  is  clearly  a  step  toward  organic  solution,  but 
the  cooking  of  proteids  renders  them  in  general  somewhat  less  soluble. 
For  the  mode  of  action  of  ptyalin,  see  below  (page  188),  where  hydrolysis 
in  the  stomach  is  briefly  discussed. 

Deglutition. — The  next  mechanism  and  set  of  movements  which  we 
have  to  consider  in  an  orderly  study  of  fligestion  are  those  of  the  process 
of  swallowing,  technically  called  deglutition.  These  have  long  been  the 
subject  of  research  on  the  part  of  anatomists  and  physiologists,  for 
both  the  mechanism  and  its  action  are  very  complex. 

The  pharynx  is  a  muscular,  membranous,  funnel-shaped  tube  con- 
necting the  mouth  and  nasal  fossae  with  the  esophagus  below  it.  The 
superior  constrictor  of  the  pharynx  is  composed  of  cross-striated  fibers, 
the  middle  constrictor  of  both  smooth  and  cross-striated  fibers,  and  the 
inferior  wholly  of  smooth  or  un-striated  muscle.  The  esophagus,  a 
muscular  tube  about  23  cm.  long  and  2  cm.  in  diameter,  connects  the 
pharynx  above  with  the  stomach  below.  The  point  at  which  it  passes 
through  the  diaphragm  is  its  narrowest  part.  Like  the  pharynx  the 
esophagus  has  three  coats,  the  outermost  being  muscular  and  con- 
sisting of  two  layers  of  fibers,  of  which  the  external  are  longitudinal  and 
the  internal  circular.  As  in  the  pharynx  also,  the  upper  part  of  the  esoph- 
agus is  of  cross-striated  fibers  chiefly  and  the  lower  part  of  smooth 
fibers.  The  muscles  of  the  upper  part  are  supplied  by  the  recurrent 
laryngeal  nerve,  while  the  vagus  supplies  the  muscles  of  the  lower  part 
of  the  tube.    The  pharyngeal  muscles  are  supplied  by  branches  from  the 


ISO  DIGESTION 

phanngeal  plexus  coming  from  the  vagus,  the  glosso-pharyngeal,  and 
the  sympathetic. 

The  process  of  swallowing  presents  for  consideration  continuous 
series  of  muscular  movements  of  a  complex  nature.  They  are  one  of  the 
best  examples  of  a  highly  developed  and  perfectly  coordinated  neuro- 
muscular mechanism.  The  tongue  arranges  the  bolus  of  food  in  the 
middle  of  its  back  surface  and  then  tips  up  anteriorly.  The  bolus  of 
food  then  partly  drops  and  is  partly  squeezed  backward  between  the 
tongue's  dorsum  and  the  hard  palate  and  between  the  anterior  pillars  of 
the  fauces.  Meanwhile  the  soft  palate  has  been  raised  and  the  posterior 
pillars  have  approximated,  the  uvula  closing  what  little  opening  remains. 
This  prevents  the  regurgitation  of  the  food-mass  into  the  mouth  or  into 
the  nasal  fossse.  By  action  of  the  upper  pharyngeal  muscles  the  pharynx 
is  raised  to  meet  the  descending  bolus.  The  larynx  is  also  raised  and 
at  the  same  time  closed  above  by  the  drawing  forward  of  its  posterior 
boundaries.  As  an  extra  safe-guard  against  drops  of  liquid  falling  into 
the  lungs,  the  vocal  cords  are  approximated  at  the  same  time.  To  the 
same  end,  and  even  more  importantly,  respiration  is  entirely  suspended 
(reflexly  by  way  of  the  glosso-pharyngeal  nerve)  during  the  entire  swal- 
lowing process.  Thus,  the  bolus  of  food  drops  into  the  grasp  of  the  con- 
strictors. These  rapidly  force  it  in  the  line  of  least  resistance  down- 
ward, where  the  inferior  constrictors  push  it  onward  into  the  muscular 
esophagus.  In  the  latter  tube  it  moves  at  first  rapidly  and  then  more 
slowly  by  t^-pical  peristalsis.  With  a  phonendoscope  the  thud  made  by 
the  bolus  dropping  into  the  stomach  can  be  often  heard. 

In  the  case  of  a  large  bolus  this  process  of  swallowing  from  the  tongue 
to  the  stomach  requires  as  much  as  six  seconds.  About  five  of  these 
seconds  are  consumed  in  the  esophagus.  As  Meltzer  showed,  when  the 
mass  of  food  swallowed  is  small  or  a  liquid  the  process  is  simpler. 

Deglutition  appears  to  have  a  controlling  center  in  the  medulla  oblon- 
gata apparently  not  far  from  the  vagal  center  and  closely  related  to  the 
center  of  respiration.  Deglutition  is  essentially  a  reflex  process,  but  it 
may  be  initiated  by  the  will.  The  act  cannot  be  carried  out  completely 
however,  unless  there  is  some  substance  passing  over  the  mucous  mem- 
branes to  reflexly  actuate  the  apparatus.  One  cannot  swallow  several 
times  in  quick  succession  because  after  the  first  or  second  swallow- 
ing there  is  no  saliva  to  furnish  afferent  nervous  impulses.  These 
nervous  influences  pass  inward  by  branches  of  the  superior  maxillary 
of  the  fifth,  of  the  superior  laryngeal,  of  the  tenth,  and  of  the  ninth  cranial 
nerve.  The  efferent  or  motor  nerves  of  deglutition  are  the  twelfth,  fifth, 
ninth,  tenth,  and  eleventh. 

The  Stomach.— 'J'h is  viscus  consists  of  two  parts,  functionally  rather 
distinct — namely,  the  funthis  and  the  antrum.  The  inlet  of  the  stomach 
above  is  the  cardia;  its  outlet  below  is  the  pylorus.  Both  are  guarded 
by  valves  which  consist  of  thickenings  of  the  circular  muscular  fibers. 
The  wall  of  the  stomach  is  composed  of  four  layers.  The  muscular 
part  of  the  gastric  wall  consists  of  two  complete  and  one  incomplete 


DIGESTION 


181 


Fig.  84 


layer  of  smooth  fibers.  The  mucous  membrane  lines  the  entire  stomach, 
but  (litters  somewhat  in  the  fundus  and  the  antrum.  It  contains  the  cells 
which  secrete  the  digestive  juices  of  the  organ.  Judging  by  the  varied 
nature  of  these  juices,  peptic,  rennic,  acrid,  etc.,  there  must  be  at  least 
three  sorts  of  cell-protoplasm  present;  it  is  not  easy,  however,  to  defi- 
nitely discriminate  more  than  two  sorts  of  cells.  The  cells  of  the  glands 
of  the  fundus  have  both  these  sorts  of  cells.  One  sort  are  irregular  epi- 
thelial cells  almost  surrounding  the  capillary  lumen  of  the  straight  tubular 
glands,  and  known  as  the  central  for  chief  or  principal)  cells.  The  other 
sort,  much  less  numerous,  are  irregular,  })olyhedral  cells,  peripheral 
to  the  central  cells,  lying  on  the  parietes  of  the  gland  and  hence  called 
parietal  cells.  The  latter  variety  are  connected  with  the  gland's  lumen 
only  by  very  fine  channels  running  between  the  central  cells  (Fig.  84). 
These  glands  have  wide  mouths  common 
to  several  tubules,  and  these  openings 
give  the  stomach  its  reticulated  appear- 
ance. They  are  lined  by  columnar  epithe- 
lium and  seem  to  be  found  in  all  parts 
of  the  stomach,  but  much  less  numerously 
in  the  antrum.  It  is  by  no  means  certain 
what  the  exact  functions  of  these  two 
kinds  of  cells  are,  but  it  is  probable  that 
the  columnar  central  cells  secrete  by  way 
of  pepsinogen  the  enzyme  pepsin,  and 
that  the  parietal  cells  produce  the  free 
hydrochloric  acid  characteristic  of  the 
stomach. 

The  cells  of  the  glands  of  the  antrum 
are  somewhat  more  cuboid  al  than  those 
of  the  fundus,  the  lumens  of  the  glands  are 
longer  and  narrower  and  no  polyhedral 
parietal  cells  are  present.  Toward  the 
pyloric  valve  these  glands  become  larger 
and  similar  in  all  apparent  respects  with 
Brunner's  glands,  so  called,  of  the  duodenum.  It  is  likely  that  the  colum- 
nar and  cuboidal  central  cells  all  over  the  stomach  secrete  both  pepsin 
and  "rennin,"  but  the  details  as  to  which  secretes  which  are  as  yet  unde- 
veloped. Besides  these  three  sorts  of  cells,  small  solitary  lymph-follicles 
are  scattered  sparingly  throughout  the  gastric  mucosa.  They  are  similar 
to  those  found  in  the  intestine  but  smaller,  and  are  like  the  follicles  of 
lymph-nodes. 

To  summarize  the  functions  so  far  as  known  at  present  of  the  various 
glands  of  the  stomach :  The  central  cells  of  the  glands  both  in  the  fundus 
and  in  the  antrmn  probably  secrete  pepsin  and  rennin,  some  of  the 
granules  (zymogens)  apparent  in  these  cells  after  resting  being  precursors 
of  pepsin  and  some  precursors  of  rennin.  The  glands  of  the  antrum 
secrete  a  form  of  pepsin  probably  less  complete  and  less  active  than  that 


Longitudinal  section  of  the  stomach 
of  the  canary  bird,  to  show  the  two 
parts,  chemical  and  mechanical:  D,  the 
duodenum;  SDr,  small  simple  tubular 
glands;  ZDr,  compound  tubular 
glands.      5/1        (Oppel.) 


182 


DIGESTION 


from  the  fundus.  The  parietal  ("oxvntic")  cells  in  the  glands  of  the 
fundus  probably  prepare  the  free  hydrochloric  acid  found  in  the  stomach, 
and  perhaps,  as  Maly  supposes,  from  the  sodium  chloride  of  the  blood 
bv  this  reaction: 

XaH,PO,  +  NaCl  =  Na,HPO^  +  HCl. 


Fig.  85 


Section  of  the  mucosa  of  tlie  cardiac  end  of  the  stomach:  a,  gland  mouth;  b,  cardiac  gland- 
tube,  "chief  cells;"  c,  parietal  cells;  d,  basement-membrane  of  connective  tissue.  This  extends 
between  the  tubules  and  carries  the  vascular  elements  to  these  structures;  e,  interglandular 
connective  tissue;   f,  general  epithelial  surface.      (Bates.) 

The  fact  that  it  is  prodiicil)lc  l)y  the  ^land.s  by  direct  stimulation  during 
fasting  seems  to  negate  the  theory  that  it  is  produced  immediately  from 
the  sodium  chloride  of  the  foofl.  It  seems  probable  that  much  remains 
to  be  learned  concerning  the  precise  functions  of  the  glands  of  the  gastric 
antrum. 

The  moyeaiext.s  of  the  .stomach  have  lojig  been  a  fertile  subject 
for  description,  but  only  recently,  with  the  use  of  the  much  revealing 


DIGESTION 


183 


Rontgen  rays,  have  we  eonie  to  possess  actual  knowledge  on  this  matter. 
The  shape  of  the  stomach  (lepicted  in  the  anatomies,  an  organ  with  an 
unbroken  greater  curvature  extending  from  the  pylorus  to  the  left  around 
the  fundus  and  up  to  the  cardia,  exists  only  immediately  after  a  large 
meal,  when  the  viscus  is  distended  with  food  and  drink.  One  sees  it  so, 
in  other  words,  only  before  the  proper  action  and  contraction  of  the  organ 
has  begun  to  make  headway  over  the  contained  mass.  Far  from  being 
a  simple  bag  closable  at  its  lower  end  by  the  pyloric  valve,  the  stomach  is 
essentially  a  double  organ  in  the  same  sense  that  the  stomach  of  the  sheep 
has  several  chambers,  although  the  omnivorous  nature  of  man  does  not 
necessitate  the  elaborate  mechanism  needed  for  rumination.    The  human 


Fig.  86 


The  stomach  of  a  ruminant  (sheep)  partly  laid  open:  a,  esophagus;  g,  retioulum;  /(,  ehanne 
for  swallowed  food;  i,  omasum,  or  psalterium;  /,  abomasum  (rennet,  or  chemical  stomach);  c,  b, 
rumen  (reservoir-stomach).      (Caru.i  and  Otto.) 


stomach  is  divided  into  parts,  the  fundus  or  left-hand  distended  portion, 
and  the  antrum,  the  active  organ  of  digestion  proper.  This  division  is 
more  obvious  functionally  than  appears  in  the  structure  of  the  post- 
mortem organ.  The  parts  are  equal  y  important,  for,  as  we  shall  see, 
the  mechanical  functions  of  the  stomach  are  at  least  as  important  as  its 
uses  in  the  way  of  chemical  digestion. 

The  fundus,  formerly  called  the  cardiac  end  of  the  stomach,  has  move- 
ments which  are  gentle  and  slow  compared  with  those  of  the  antrum  and 
of  the  small  intestine.  The  fundus  is  largely  a  reservoir,  and  its  motions 
correspond  to  such  a  use.  They  are  of  a  gentle  and  slowly  peristaltic 
nature  just  powerful  enough  to  keep  the  antrum  supplied  with  material 
for  its  solution  into  chyme.     It  app?ars  from  work  by  Austin  and  by 


184 


DIGESTION 


Cannon,  the  former  Avorking  chemically  and  the  latter  with  the  Rontgen 
rays  on  cats,  that  the  food  as  swallowed  into  the  stomach  may  remain 
in  the  fundus  an  hour  or  more  practically  undisturbed.  This  allows 
amylolytic  digestion  by  the  ptyalin  to  continue,  the  contents  for  a  time 
often  not  being  mixed  with  the  hydrochloric  acid  surrounding  it  in  the 
stomach  wall,  and  so  remaining  alkaline.  The  circular  muscular  fibers 
of  the  stomach's  fundus  make  up  the  bulk  of  the  musculature  and  by 
gradual  tonic  contraction  combined  with  a  slow  peristalsis  (occurring  in 
the  dog  in  waves  three  or  five  times  per  minute,  according  to  Lommel) 
the  size  of  the  fundus  is  gradually  reduced  as  its  contents  are  passed 
through  the  sphincter  of  the  antrum  into  the  latter  portion  of  the  stomach. 
These  gentle  peristaltic  waves  probably  are  continuous  with  those 
descending  the  esophagus,  and  they  pass  from  the  cardiac  end  of  the  viscus 
to  the  pyloric  valve.     Combined  with  this  there  may  be  or  not  gentle 

Fig.  87 


The  human  sfomaoh.  drawn  ffrom  a  dissecting-room  specimen)  so  as  to  make  clear  the 
two  functional  parts  of  the  stomach.      (Hutchison.) 


swinging  and  tipping  movements  determined  by  the  longitudinal  and  the 
oblif|ue  fibers  of  the  gastric  wall.  It  is  brought  about  by  the  full  final 
contraction  of  the  circular  fibers  of  the  fundus  that  when  the  stomach  is 
empty  it  has  somewhat  the  shape  of  a  boot  fthe  antrum  representing  the 
foot),  fixed  above  by  the  lower  end  of  the  esopliagus.  The  stomach  is 
seen  to  be  an  exceedingly  adaptable  organ  so  far  as  its  shape  is  concerned, 
a  faculty  which  the  variety  of  direction  of  the  muscular  fibers  makes 
possible.  AMicn  nearly  empty  it  is  probable  that  the  longitudinal  fibers 
also  contract  somewhat,  still  further  lessening  the  size  of  the  viscus.  It 
is  thus  that  the  food  in  the  reservoir  is  gradually  anrl  entirely  forced 
onward  into  the  antrum,  the  walls  apparently  adjusting  themselves 
jjcrfectly  to  the  volume  of  their  contents. 

The  arifrvm  within  a  fcAV  minutes  after  (he  ingestion  of  a  meal  begins 
to  show  slight  annular  contractions,  rhythmic  in  character,  near  the 


DIGESTION 


185 


pylorus,  for  some  of  the  food  taken  into  the  now  distended  stomach 
went  directly  into  this  portion  of  the  viscus,  no  dividing  line  between 
fundus  and  antrum  being  as  yet  present.  Soon,  however,  the  antrum 
begins  to  be  shut  oli"  from  the  fundus  by  contraction  of  its  sphincter, 
and  it  remains  a  distinct  portion  of  the  stomach  until  the  viscus  is  quite 
emptied  into  the  duodenum.  This  is  a  period  which  varies  with  the  sort 
and  amount  of  food  eaten,  from  one  to  seven  or  even  more  hours.  The 
movements  of  the  antrum  are  rhythmically  peristaltic,  and  they  serve  by 
their  strong  compression  against  the  resisting  pylorus  to  grind  and  squeeze 
whatever  lumps  of  food  may  be  present  and  are  not  too  hard  into  a 
soft  pidtaceous  mass.  The  con- 
tained pepsin,  the  hydrochloric  Fig.  ss 
acid,  the  mucus,  and  the  heat 
of  the  organ  materially  aid  in 
this  process  of  chymification. 
The  antrum  contracts  in  the 
cat  about  once  in  ten  seconds, 
according  to  Cannon,  probably 
as  a  continuation  of  the  peri- 
stalsis over  the  fimdus,  said  by 
Lommel  to  occur  in  the  dog: 
somewhat  less  frequently.  The 
small  intestine  is  much  more 
delicate  and  sensitive  than  is  the 
stomach,  and  would  be  disturbed 
not  a  little  by  the  reception  of 
lumps  or  hard  masses  of  solid 
food. 

The  pyloric  valve  opens  peri- 
odically and  in  a  rhythmic  way. 
It  is  actuated  by  probably  ner- 
vous influences  sent  out  from 
the  antrum's  walls.  It  is  stim- 
ulated to  relaxation,  that  is,  to 
open  (according  to  Cannon),  by 
strong  acidity  in  the  antrum, 
and  it  is  closed   by  acidity  in 

the  duodenum  beyond  it.  Thus,  in  cats  fed  on  a  proteid  meal  the  form- 
ing chyme  remains  much  longer  in  the  antrum  than  when  the  food  is 
carbohydrate.  Protein  does  not  absorb  the  free  acid  of  the  stomach  as 
carbohydrate  does,  thus  leaving  the  acid  free  to  stimulate  the  pylorus 
to  contraction.  The  carbohydrate  takes  large  quantities  of  the  acid 
early  into  the  duodenum,  and  its  presence  there  keeps  the  valve  shut. 
The  proteid  has  thus  longer  time  for  digestion  in  the  antrum.  To 
remain  there  would  be  useless  in  case  of  carbohydrates.  Every  two  or 
three  minutes,  however,  in  the  cat,  the  pyloric  valve  relaxes  and  allows 
part  of  the  liquid  portion  of  the  chyme  to  escape  into  the  intestine.     The 


Gizzard    of   a   bird:    .4,  contracted   state; 
B,  relaxed  state.      (Jarrod.) 


1S6  DIGESTION 

inspiratory  contraction  of  the  diaphragm  probably  aids  somewhat 
in  this  stjueezino-  work  of  the  antrum,  for  it  has  been  found  that  the 
antrum  is  moved  bv  the  descending  diaphragm,  but  much  less  than  is 
the  cardiac  portion  of  the  stomach. 

Vomiting  is  the  process  by  which  the  stomach  normally  unloads 
itself  of  excessive  or  irritating  food.  Because  of  its  close  connection 
with  the  central  nervous  system  it  is  also  a  frequent  symptom  of  the  onset 
of  many  diseases,  especially  in  children.  In  young  infants  vomiting 
is  a  purely  normal  process  very  often,  and  allows  of  the  easy  unloading 
of  a  stomach  into  which  too  much  has  been  put.  In  adults  the  process 
is  usually  preceded  by  the  most  unpleasant  and  complex  feeling  of  nausea, 
the  most  conspicuous  outward  signs  of  which  are  usually  a  general 
peripheral  vaso-constriction  and  a  flow  of  saliva.  Next  comes  retching, 
in  which  the  feeling  of  nausea  is  intensified  and  the  diaphragm  makes 
powerful  inspiratory  contraction,  the  glottis  being  closed.  Then  the 
fauces  open  wide,  the  tongue  takes  the  form  of  a  rounded  trough,  the 
abdominal  muscles  vigorously  contract,  and  simultaneously  the  dia- 
phragm. Thus  the  stomach  is  strongly  squeezed  between  two  approach- 
ing resistances — below  the  mass  of  the  intestines,  etc.,  and  above  the 
rigid  diaphragm.  Under  this  gastric  pressure  the  cardiac  valve,  recently 
closed,  bursts  open  and  the  stomach-contents  pour  upward  through  the 
now  wide-open  glottis,  pharynx,  and  mouth.  The  nasal  passages  are 
shut  off  (save  in  very  violent  emesis)  by  the  closure  of  the  soft  palate,  etc., 
in  the  same  manner  as  in  swallowing.  In  children's  vomiting  the  mus- 
cular coats  of  the  stomach  appear  to  be  much  more  active  than  in  adults. 

It  is  supposed  that  there  is  a  center  which  coordinates  the  numerous 
muscular  and  glandular  tissues  of  nausea  and  vomiting.  This  is  prob- 
ably in  the  medulla  near  the  respiratory  center  and  the  center  of  degluti- 
tion. The  nerves  chiefly  concerned  are  the  tenth,  the  ninth,  the  phrenics, 
and  the  other  spinal  nerves,  the  tenth  bearing  apparently  the  greater 
part  of  the  afferent  impulses. 

Emetics,  substances  causing  emesis  or  vomiting,  are  of  interest  because 
they  suggest  the  various  ways  in  which  this  reflex  act  may  be  instigated. 
It  may  also  be  started  mechanically,  for  example,  by  tickling  the  fauces 
with  the  finger  or  with  a  feather.  General  emetics  are  substances 
(for  example  apomorphin)  which  stimulate  the  vomiting-center  in  the 
medulla;  just  how  they  do  so  is  unknown.  Injection  into  the  circulation 
is  the  most  direct  way  of  using  this  sort  of  emetic.  Local  emetics  irritate 
the  nerves  and  muscles  of  the  stomach  directly  and  thus  reflexly  cause 
vomiting.  ]\Iustard  is  a  common  example  of  these.  Some  emetics 
act  in  both  of  these  ways,  for  example,  tartar  emetic.  Anti-emetics 
are  drugs  which  r|uiet  the  tendency  to  vomit.  They  also  may  act  locally 
or  generally,  for  example,  morphine,  which  quiets  at  once  the  vomiting- 
center  and  the  neuromuscular  mechanism  in  the  stomach-walls. 

The  gastkic  juice  is  the  product  of  glan(hilar  activity  in  the 
stomach.  It  is  a  clear,  nearly  colork^ss  li(|uid  of  a  specific  gravity  of 
about    1(J().";,  but  variable,  a  sour  taste,  and  an  odor  peculiar  to  itself. 


DIGESTION 


187 


One  of  its  characteristics  is  its  permanence  in  the  air,  putrefaction  never 
occurrini^.  The  average  daily  cjiiantity  is  hard  to  determine,  but  in  a 
man  is  very  hkely  from  two  to  five  Hters.  In  various  animals  its  strength 
is  very  different.  In  the  dog,  for  example,  it  is  about  three  times  as  strong 
as  in  man,  so  that  this  animal  can  afl'ord  to  bolt  its  food.  In  composition 
gastric  juice  probably  varies  greatly  at  different  times  according  to  the 
digestive  habits  of  the  individual.  Schmidt's  analyses  are  cjuoted  as 
often  as  any,  and  it  is  interesting  to  compare  his  determinations  of  the 
gastric  juice  from  an  omnivorous  animal  (man),  from  a  carnivorous 
animal  (dog),  and  from  an  herbivorous  animal  (sheep).  It  is  likely  that 
the  strength  accorded  to  man's  gastric  juice  is  weaker  than  the  average, 
especially  in  hydrochloric  acid,  which  may  be  often  1  or  even  2  per  cent. 

Fig.  89 


Human  gastric  muco.sa,  peptic  region,  vertical  section:  a,  muscularis  mucosae;  6,  subglandu- 
lar  lymph  plexus;  c,  intraglandular  Ij-mph  sinus;  d,  suggestion  of  an  external  plexus  of  IjTnph 
channels;   /,  submucous  lymph  plexus.      (Loven.) 


Composition  of  Gastric  Juice  (Schmidt). 


Constituents. 

Man. 

Dog. 

Sheep. 

Water 

Organic  matter      .... 

HCl,  free 

NaCI 

KCI 

CaCI^ 

Ca,2  (PC,)  1 

Mg32(PO,) 

FePO,         j 

NH.Cl 

994.404 
3 .  195 

+0.200 
1 .  465 
0.550 
0.061 

0.125 

973.062 
17.127 
3.050 
2.507 
1.125 
0.624 
1.729 
0 .  226 

.  0.082 
0.468 

986.143 
4.055 
1.234 
4.369 
1.518 
0.114    . 
1.182 
0.577 
0.331 
0.473 

The  organic  matter  consists  of  pepsin,  "rennin,"  lipase,  and  traces  of 
a  proteid  and  of  mucin.  Secretion  of  gastric  juice  apparently  does  not 
continue  after  the  stomach  becomes  empty.  It  is  readily  induced, 
however,  by  the  introduction  of  anv  solid  substance  into  the  organ,  or 


188 


DIGESTION 


bv  the  sight,  taste,  smell,  or  even  thought  of  food  when  the  mdividual 
is  himgrv  to  some  extent.  For  experimental  purposes  gastric  juice  is 
usually  obtained  from  dogs  in  which  a  gastric  fistula  opening  outward 
on  the  belly  has  been  established.  Sometimes  an  esophageal  fistula 
opening  on  the  exterior  is  also  made  and  so  arranged  that  food  passes  at 
the  will  of  the  observer  either  into  the  stomach  or  directly  outside  the 
body.  To  obtain  a  supply  of  gastric  juice  it  is  only  necessary,  then,  to 
give  the  animal  in  this  way  a  fictitious  meal,  whereupon  reflex  neural 
impulses  cause  a  copious  flow  of  the  desired  liquid,  which  is  removed 
through  the  gastric  fistula. 


Fig.  90 


Fig.  91 


-=^:^s^^^^= 


Two  sorts  of  glands  found  in  the  gastric  mucosa. 


_  Digestion  in  the  stomach  is  brought  about  chiefly  by  three 
enzymes  or  ferments — pepsin,  rennin,  and  lipase — and  by  the  hydrochloric 
acid.  The  action  of  the  pytalin,  too,  secreted  in  the  mouth,  occurs  also 
for  the  most  part  in  the  gastric  fundus.  We  will  next  briefly  examine 
into  the  chemical  changes  produced  in  various  classes  of  foods  by  these 
still   mysterious  agents. 

Piyalhi  appears  to  have  been  first  isolated  from  saliva  by  Mialke  and 
in  a  somewliat  purer  state  by  CVjnheim;  so  far  it  has  not  been  obtained 
free  from  a<lmixtnre  witli  protein  and  various  metallic  salts.     It  seems 


DIGESTION 


189 


to  be  very  similar  to  faccording  to  Abderhaldcn  identical  with)  the  enzyme 
amylopsin  secreted  by  the  pancreas  as  one  of  its  external  secretions. 
It  is,  however,  weaker  than  amylopsin,  and  does  not  under  the  normal 
conditions  of  digestion  carry  the  zymolytic  process  so  far — mainly  the 
same  difference  which  obtains  between  pepsin  and  trypsin.  It  acts  in 
an  alkaline,  neutral,  or  even  slightly  acid  medium,  free  acid,  even  0.003 
per  cent.,  being,  however,  c[uickly  destructive  of  its  peculiar  powers. 
In  general  it  seems  accurate  to  say  that  ptyalin  acts  best  in  a  neutral 
medium,  as  Chittenden  seems  to  have  proved,  such  as  may  be  supposed, 
indeed,  to  obtain  in  the  mass  of  food  as  taken  into  and  kept  for  a  consider- 
able while  in  the  fundus  of  the  stomach.  The  chemical  composition  of 
ptyalin  cannot  be  statefl  with  any  degree  of  certainty  at  present,  a  state- 
ment equally  true  of  all  other  enzymes. 


Fig.  92 


, DIASTASE. 

-. —  PEPSIN. 

—  .-"RENNIN." 

-...-   INVERTING  AGENTS. 


, , . TRYPSIN. 

_.. .. LIPASE. 

EREPSIN. 

> ... ...   BACTERIA. 


A 


.  / :        \  \\ 


//;• 


•.  W 


/ 


/ 


,•* 

^.^    >;;*..-" 

A<- 

*..  \ 

ALKALINE 

NEUTRAL 

ALKALINE 

ALKALINE 

MOUTH   AND 

AND  ACID 

SMALL 

LARGE 

ESOPHAGUS. 

STOMACH. 

INTESTINE. 

INTESTINE. 

This  diagram  shows,  after  the  manner  of  the  graphic  method,  the  various  chemical  digestive 
agents  and  their  respective  times  of  action.  In  the  complexity  of  interactions  in  the  alimentary 
canal  it  must  be  pre-supposed,  however,  that  the  conditions  are  more  variable  than  any  diagram 
could  indicate.      (Modernized  from  Krukenberg.) 


AYe  consider  the  action  of  ptyalin,  secreted  in  the  mouth,  under  the 
heading  of  the  stomach  because  its  chief  action  is  performed  in  that 
viscus  and  not  in  the  mouth,  as  has  already  been  suggested.  The  food 
remains  in  the  stomach  liable  to  diastatic  digestion  an  hour  for  every 
minute,  often  for  every  second,  that  it  remains  in  the  mouth. 

Ptyalin  brings  about  the  conversion  of  starch  and  of  glycogen  into 
sugar,  the  form  of  sugar  produced  by  this  ferment  being  finally  maltose. 
The  method  of  this  change  is  hydrolysis:  the  absorption  of  water  followed 
by  a  splitting  of  the  amylodextrin  or  soluble  starch  so  produced  into 
molecules  of  maltose  and  probably,  at  first,  also  of  dextrin.  Because 
we  are  still  ignorant  of  the  exact  molecule  of  starch  (knowing  only  that  it 
is  some  multiple  of  (CgHj^O^)  perhaps  (CgHjgOJjo'  the  precise  reaction 


190  DIGESTION 

cannot  be  given,  Neumeister,  recognizing  erythrodextrin  as  the  first 
splitting-product  from  the  amylodextrin  (so  named  because  with  iodine  it 
gives  a  red  coloration),  supposes  that  at  least  three  forms  of  dextrin 
are  successively  produced,  which,  because  they  give  us  color  with  iodine, 
have  received  the  name  achroodextrins.  These  he  named,  respectively, 
alpha-achroodextrin,  beta-achroodextrin,  and  gamma-achroodextrin. 
Neumeister's  theory  of  this  hydrolysis,  therefore,  may  be  represented  in 
a  table,  thus: 

Starch  (amylose). 

Soluble  starch  (amj-lodextrin). 


Erythrodextrin.     Maltose. 


)6dex 


« — Achroodextrin.     Maltose. 


li — Achroodextrin.     Maltose. 


}' — Achroodextrin  (maltodextrin).     Maltose. 
Maltose. 

Musculus  and  Gruber  corroborated  this  supposition,  but  still  the 
proof  that  the  three  achroodextrins  named  are  proper  substances,  stable 
and  constant  in  composition,  is  far  from  conclusive.  Ptyalin,  unlike  the 
dilute  mineral  acids,  is  unable  to  continue  the  splitting-reaction  of  the 
maltose  into  glucose  or  grape-sugar.  Maltose,  however,  is  not  absorbable 
through  the  intestinal  wall,  but  is  inverted  into  dextrose  before  absorp- 
tion into  the  blood  takes  place.  This  result  is  produced  by  the  hydro-' 
chloric  acid  of  the  stomach,  and  especially  by  the  enzyme  maltase  (or 
glucase)  of  the  succus  entericus.  Were  we  to  represent  the  hydrolytic 
cleavage  in  the  simplest  possible  equation,  it  would  be 

SCCeH.oOs)  +  2(H,0)  =  C^H.oOs  +  C,,H,,0„. 
Starch.  Dextrose.       Maltose. 

But  this  is  misleading  in  a  sense,  for  the  reaction  is  very  much  more  com- 
plex than  the  equation  would  indicate,  starch,  for  example,  not  being 
CgII,(,Oj  but  some  multiple  of  that.  If,  then,  we  take  m,  n,  and  p  as  the 
unknown  co-cfficicnts  of  the  starch,  water,  and  dextrin  molecules  con- 
cerned, respectively,  we  have  (Moore): 

(CeH,o05)m  +  (H,0)n  =  'J  ((',.H,/)„)  (H,())  +  "=^  (C«H,„05)p 
^  P 

as  the  most  precise  formnhi  of  diustatic  action  at  present  obtainable, 
and  this  is  much  more  descriptive  of  the  j)n)cess  than  the  previous 
formula  given. 


DIGESTION  191 

Pepsin  is  a  proteolytic  enzyme,  secreted  by  the  central  cells  of  the 
gastric  mucous  membrane,  es})ecially  by  those  of  the  fundus.  The 
cray-fish  secretes  its  pepsin  in  the  mouth  just  as  men  produce  ptyalin 
there,  but  use  it  largely  in  the  stomach's  undisturl)ed  fundus.  Pepsin 
is  present  in  the  stomach  of  the  child  at  birth,  but  in  many  animals, 
especially  the  carnivora,  for  example  the  cat  and  the  dog  (Moriggia), 
it  makes  its  appearance  only  two  weeks  or  so  after  l)irth.  It  differs 
from  most  enzymes  in  reciuiring  an  acid  medium  for  its  activity.  In  an 
alkaline  or  even  in  a  neutral  medium  pepsin  is  rapidly  destroyed.  Indeed 
some  have  supposed  that  the  really  active  proteolytic  agent  is  pepsin- 
hydrochloric-acid  or  even  the  acid  alone.  There  is  no  proof  that  this 
is  a  true  compound,  while  Maly  has  shown  that  other  acids  may  serve 
in  place  of  the  hydrochloric  acid.  Nitric  acid  is  the  best  substitute, 
but  lactic,  phosphoric,  and  three  or  four  other  common  acids  also  serve 
experimentally  this  function  of  giving  pepsin  its  "required  acid  medium." 
Maly's  work  suggests  that  part  of  the  action  of  the  acid  may  be  to  swell 
up  and  soften  the  proteid,  and  those  acids  which  are  most  active  in  this 
respect  are  those  which  are  also  most  effective  in  combination  with  the 
pepsin.  The  most  recent  theory  is  that  the  pepsin  acts  solely  as  a  coupler 
between  the  protein  and  the  acid,  the  latter  doing  the  hydrolyzing 
work.  This  enzyme  acts  most  rapidly  at  a  temperature  2^  or  3°  above 
the  normal  temperature  of  the  body,  but  is  destroyed  at  about  80°  C. 
(dry  at  100°),  a  degree  of  heat  about  12°  higher  than  that  which  destroys 
ptyalin.  As  the  temperature  falls  action  becomes  slower  and  quite  ceases 
at  zero.  The  pepsin  of  commerce  is  a  gastric  extract,  containing  usually 
either  lactose  or  starch. 

The  function  of  pepsin  has  long  been  said  to  be  to  hydrolyze  proteids 
and  albuminoids  so  that  they  may  be  absorbed  into  the  circulation  and 
thus  feed  the  organism.  Pepsin's  solvent  power  over  different  forms  of 
proteid  varies  exceedingly.  Casein  is  perhaps  the  most  easily  hvdrolyzed 
of  all  the  proteids,  raw  meat  more  easily  than  cooked  meat,  beef  more 
readily  (Cummens  and  Chittenden)  than  fish,  and  animal  proteids  more 
easily  than  those  of  vegetal  origin. 

Pepsin  hvdrolyzes  proteids  into  peptone,  probably  into  polypeptids,  and 
possibly  further  into  the  amido-acids  even,  as  the  final  products  of  its 
action.  The  intermediate  substances  produced  are  variously  named 
and  as  variously  described  by  different  chemists,  and  must  be  considered 
as  yet  uncertain.  Even  less  is  known  about  the  molecular  structure 
of  proteids  and  albuminoids  than  about  that  of  starch,  and  here  even 
more  than  there  are  the  way-products  undetermined.  Two  of  these 
way-products,  however,  are  fairly  well  known,  namely,  the  albimiinate 
syntonin  (acid-albumin)  and  proteose  ("propeptone,"  albumose,  globu- 
lose,  vitellose,  gelatinose,  elastose,  etc.).  It  is  very  possible  that  syntonin 
may  not  be  formed  from  all  the  proteid  undergoing  digestion,  but  usually 
the  proteid  swells  all  through  owing  to  the  combined  action  of  the  acid 
and  pepsin,  the  softened  mass  then  dissolving.  By  hydrolysis  (absorp- 
tion of  water  and  molecular  cleavage)  the  syntonin  then  splits  into  soluble 
proteoses.     The  debated  question  is  largely  as  to  how  many  different 


192  DIGESTION 

sorts  of  proteoses  follow  this  as  successive  cleavage-products  before  the 
mass  becomes  peptone  or  polypeptids.  The  polypeptids  are  as  yet 
ill-defined  component  parts  apparently  of  peptones.  These  have  already 
been  synthesized  artificially  from  their  constituents;  perhaps  proteids 
themselves  will  be  made  before  long.  (See  below.)  Kiihne  and  Neu- 
meister  suppose  that  two  proteoses  intervene  between  the  syntonin  and 
peptone  called  primary  and  secondary  proteoses  respectively.  Pick 
finds  reason  to  believe  that  there  are  four  of  these.  In  the  great  un- 
certainty attending  the  details  of  peptic  hydrolysis  at  present  it  is  almost 
useless  to  study  the  often  contradictory  theories  of  the  matter  farther. 
It  is  almost  enough  to  suppose  that  the  pepsin  and  acid  (or  the  latter 
alone?)  produce  successively  syntonin,  then  two  or  more  proteoses, 
then  one  or  more  peptones,  and  possibly  even  amido-acids,  each  substance 
having  a  simpler  and  probably  smaller  molecule  than  its  immediate 
predecessor.     In  schematic  and  probably  incomplete  form: 

Proteid. 

Syntonin. 

Proto-proteose. 

Deutero-proteose . 

Ampho-peptone. 

In  this  schema  the  "ampho"  of  the  peptone  implies  the  probable  presence 
of  two  sorts  of  peptone,  sometimes  called  hemi-peptones  and  anti- 
peptones  respectively.  Simpler  than  the  peptones  are  substances, 
polypeptids,  found  by  Pfaundler,  E.  Fischer,  Salaskin,  etc.,  which  are 
probably  combinations  of  amido-acids — for  example,  leucinimide.  The 
molecular  weights  of  these  and  simpler  decomposition-products  of  peptic 
hydrolysis  are  probably  not  over  5  per  cent,  of  that  of  the  proteid  with 
which  the  digestive  process  started.  These  obviously  are,  therefore, 
much  more  suitable  materials  for  tissue-building  than  more  complex 
and  unstable  substances.  For  the  body-protoplasm  to  try  to  build 
protoplasmic  tissue  out  of  proteids,  or  peptones  even,  were  much  as  if 
a  contractor  should  attempt  to  make  a  satisfactory  brick  house  out  of 
second-hand  bricks  which  had  not  been  taken  apart  and  cleaned,  but  used 
ratlier  in  the  large  masses  in  which  the  former  walls  had  fallen.  In  the 
case  of  digestion  by  acid  and  pepsin  it  is  still  in  doulit  just  how  complete 
the  separation  and  renovation  of  the  proteid-materials  are.  There  is 
some  evidence  (Mann)  that  the  peptic  process  is  one  of  aiding  the  dis- 
integrating powers  of  the  hydrogen  and  hvdroxyl  ions  in  the  epithelium. 
'  Rennin"  is  the  second  of  the  enzymes  so  far  isolated  from  the  secre- 
tion-product of  the  stomach.  It  may  be  but  an  aspect  of  pepsin.  Its 
function  if  a  separate  enzyme  is  to  coagulate  milk  and  to  do  probal)ly 
other  things  not  yet  determined,  for  it  is  secreted  by  the  stomachs  of  both 
birds  and  fishes,  to  wln'ch  of  course  milk  is  for  the  most  part  quite 
unknown.     Like  pepsin,  rennin  acts  only  in  an  acid  medium.     As  has 


DIGESTION  193 

been  noted  alreafly,  rennin  is  secreted  by  the  central  cells  of  the  gastric 
mucous  glands  coining  apparently  from  different  zymogenic  granules 
in  the  same  cells  that  prochice  pepsin,  these  needing  only  reaction  with 
acid  to  produce  pepsin  and  rennin  respectively.  Like  pepsin,  the  fundic 
glands  produce  it  in  much  larger  proportion  than  do  the  glands  of  the 
antrum.  Rennin  has  never  been  isolated;  its  optimum  temperature  is 
about  40°  C,  and  its  action  ceases  at  somewhat  above  zero.  It  is 
destroyed  by  a  lower  degree  of  heat  than  are  most  enzymes,  namely  at 
63°  in  acid  medium  and  at  70°  in  a  neutral  medium.  Rennet,  the  dried 
fourth  stomach  of  the  calf,  has  been  used  for  many  centuries  to  curdle 
milk  for  the  purpose  of  making  cheese.  Why  the  caseinogen,  the  soluble 
proteid  of  milk,  requires  coagulating  before  being  hydrolyzed  by  the 
proteolytic  enzymes  is  quite  unknown,  and  it  is  especially  hard  to  under- 
stand because  the  acidity  of  the  gastric  juice  is  sufficient  after  a  while 
to  bring  about  this  coagulation.  Perhaps  the  coagulation  is  required 
promptly  on  the  entrance  of  food  into  the  stomach,  more  promptly  than 
the  acid  could  do  it  in  the  relatively  undisturbed  fundus.  But  it  is  more 
likely  that  the  rennin  in  some  undiscovered  way  actually  starts  the 
hydrolysis  of  the  milk-proteid,  and  still  more  likely,  as  already  has  been 
noted,  that  rennin  has  important  functions  as  yet  quite  unguessed. 
The  coagulation  of  milk  in  the  stomach  may  even  be  a  defect  produced 
by  the  pepsin,  since  Pawlow  claims  that  all  proteolytic  enzymes  coagulate 
caseinogen.  As  has  been  said,  rennin  is  perhaps  only  some  chemical 
aspect  of  pepsin.  We  may  possibly  be  even  mistaking  rennin  for  what 
is  really  an  anti-rennin  (an  opponent  of  coagulation)  in  process  of  evolu- 
tion. In  the  present  ignorance  of  proteids  themselves  and  of  their 
metabolism  such  numerous  doubts  in  description  and  in  theory  are 
inevitable. 

The  mode  of  action  of  rennin  in  coagulating  caseinogen  to  casein 
is  partly  homologous  to  the  coagulation  of  blood  and  some  other  body- 
liquids  by  thrombin,  but  is  not  wholly  similar.  Caseinogen  is  the 
protein  of  milk,  and  is  apparently  a  nucleo-proteid  soluble  in  the  normal 
fluid.  On  the  addition  of  rennin  to  milk,  calcium  phosphate  always 
being  present,  this  nucleo-proteid  is  made  to  absorb  water  and  to  split 
up  into  paracaseinic  acid  and  an  albumin  by  the  usual  process  of  hydro- 
lytic  cleavage.  At  least  two  new  proteins  are  produced  by  this  splitting 
process.  One  of  these,  casein  (calcium  paracaseinate),  being  insoluble, 
falls  as  a  precipitate,  the  curd.  The  other  is  a  whey-globulin  which 
remains  in  solution,  possibly  with  a  third,  an  albumose,  in  small 
amount.  Whether  the  reaction  in  the  case  of  human  milk  is  quite  like 
this  or  not  is  in  some  slight  degree  of  doubt,  as  nearly  all  the  literature 
on  the  subject  relates  to  the  curdling  of  cows'  milk.  If  the  calcium 
phosphate  be  removed  from  the  milk  entirely,  casein  is  not  thrown 
down.  Some  have  thought  that  in  this  coagulating  process  the  action 
of  the  calcium  was  not  to  help  the  first  reaction,  changing  the  caseinogen 
to  casein,  so  much  as  to  assist  in  the  separation  of  the  two  cleavage- 
proteids,  casein  and  whey-proteid.  The  details  of  the  process  are,  in- 
13  . 


194  DIGESTION 

deed,  as  yet  much  in  doubt,  and  here,  as  elsewhere,  hypothesis  is  a  poor 
substitute  for  facts.  ]Milk  is  curdled  also  by  an  excess  of  acid,  but  that 
its  normal  coagulation  is  not  due  to  the  acid  of  the  stomach,  but  to  the 
rennin's  activity,  is  readily  presumed  by  the  fact  that  neutral  rennin 
promptly  coagulates  alkaline  milk,  no  acid  being  concerned  at  any  time, 
while  rennin  always  is  present  in  the  human  stomach  from  birth  onward 
(Heintz).  Bacteria  cause  the  curdling  of  milk  after  a  time,  but  indi- 
rectly, by  bringing  about  the  presence  of  lactic  acid,  which  curdles  the 
milk.  (The  peptic  digestion  of  casein  produces  paranuclein,  which 
gradually  dissolves.) 

Lipase  (steapsin)  has  been  found  in  the  human  stomach  by  Volhard. 
Aside  from  the  fact  that  it  acts  only  on  emulsified  fats  (e.  g.,  that  of  milk), 
little  is  as  yet  known  about  its  work  in  this  organ. 

Hydrochloric  acid  as  found  in  the  stomach  undoubtedly  exerts  some 
slight  hydrolyzing  action  on  the  disaccharides  (cane-sugar,  lactose,  and 
maltose),  bringing  about  thus  their  "inversion."  A  special  enzyme 
exists  in  the  succus  entericus  (page  207),  for  this  purpose,  called 
invertase,  and  most  of  the  maltose,  made  by  the  hydrolysis  of  carbo- 
hydrates, is  doubtless  inverted  through  the  agency  of  this  ferment  and 
not  by  acid.  Lehmann  found  invert-sugar  in  the  stomach  of  rabbits 
fed  on  beets,  while  Seegen  invariably  obtained  it  from  the  stomachs  of 
dogs  fed  on  saccharose.  No  enzyme  with  an  inverting  power  has  been 
found  in  the  stomach. 

C,,H,,0„  +  H,0  =  2(CeH,A) 

Maltose.        Water.      Dextrose. 

It  is  as  dextrose  that  most  of  the  hydrolyzed  carbohydrate  is  absorbed 
through  into  the  capillaries  of  the  intestinah  villi.  This  hydrolytic  in- 
version performed  in  the  stomach  by  the  dilute  hydrochloric  acid  is 
perhaps  small  in  amount,  but  is  of  theoretic  importance. 

When  the  acid  reaches  the  duodenum  it  reacts  on  the  prosecretin  from 
the  gut-wall  and  produces  secretin  (see  below). 

Aside  from  its  hydrolytic  powers  this  acid  is  a  powerful  antiseptic, 
as  are  most  other  acids.  The  importance  of  this  action  we  have  no  means 
of  estimating,  but  it  must  be  considerable,  for  the  bacteria  which  enter 
the  stomach  with  the  food  and  drink  are  of  numberless  varieties  and 
of  vast  number.  Some  of  these  unchecked  would  derange  all  normal 
digestion,  while  others  wouki  cause  the  illness  or  death  of  the  indivi(hial. 
The  tubercle  bacilli  is  not  destroyed  by  gastric  juice,  but  the  germs 
of  anthrax  and  of  cholera  are  cjuickly  killed.  Perhaps  in  the  long  run 
the  antiseptic  action  of  the  hydrochloric  acid  against  the  organisms  of 
ordinary  jjutrffaction  are  more  important  to  man  than  its  destruction 
of  the  virulent  germs  of  disease. 

The  Stomach's  Functions. — It  will  serve  to  fix  the  status  of  the 
stomach  in  mind  if  its  functions  are  arranged  in  a  schematic  list.  Ten 
sorts  of  usefulness  may  Ije  noted,  varying  much  in  importance,  but  all 
of  Ijenefit  to  the  organism,  the  order  in  which  they  are  given  here  being 
apparently,  in  a  g(  iieriil  way,  that  of  their  rehitive  iinj)ortance. 


DIGESTION  195 

1.  As  perhaps  first  in  cons?f[uence  the  stomach  is  a  reservoir  for  food 
and  drink.  Were  there  no  such  dilatation  in  the  aUmentary  canal  the 
taking  of  ordinary  food  in  meals  would  be  impracticable,  and  man  would 
be  in  a  somewhat  literal  sense  the  servant  and  not  the  master  of  his 
digestive  functions.  Now  that  the  stomach  is  occasionally  removed 
because  of  otherwise  fatal  disease,  there  is  opportunity  to  observe 
the  value  of  the  organ  in  this  direction,  for  this  function  alone  is  unrepre- 
sented elsewhere  in  the  alimentary  canal.  Stomachs  vary  much  in 
size  in  different  individals,  and  are  liable  to  functional  distention  as 
well  as  to  almost  tubular  contraction,  as  already  has  been  noted.  A 
fair  estimate  of  the  size  of  an  average  adult  fundus  in  a  filled  condition 
is  perhaps  a  liter.  By  the  ever-compressing  force  of  this  fundic  reser- 
voir the  antrum  is  kept  supplied  with  material  on  which  to  act,  some- 
what as  the  auricles  of  the  heart  are  mainly  reservoirs  for  the  prompt 
filling  of  the  more  active  ventricles. 

2.  The  second  in  importance  of  the  functions  is  perhaps  the  hydro- 
lyzing  of  proteids  and  of  alhuminoids  to  forms  which  are  absorbable 
from  the  gut  farther  on.  It  seems  probable  that  there  is  more  difference 
between  peptic  and  tryptic  proteolysis  than  is  now  generally  recognized. 
It  is  hard  to  define  the  relative  importance  of  these  two  to  the  organ- 
ism, yet  the  stomachless  mammal  probably  thrives  much  better  mthout 
pepsin  than  he  could  without  trypsin. 

3.  Another  function  of  the  stomach,  close  or  even  equal  to  the  last- 
mentioned  in  importance,  is  the  digestion  of  soluble  carbohydrates  begun 
by  the  ptyalin  in  the  mouth.  The  contents  of  the  gastric  fundus  being 
sometimes  undisturbed  for  hours  even,  the  major  part  of  amylolysis  takes 
place  sometimes  at  least  in  the  stomach.  Here  the  advancing  neutrality 
of  reaction  and  perhaps  soon  a  slight  degree  of  acidity  furnishes  the 
ptyalin  its  best  medium  for  action  on  starches  and  on  sugars.  As  we 
have  seen,  the  greater  the  proportion  of  carbohydrates  in  the  stomach, 
absorbing  the  free  hydrochloric  acid  and  so  removing  the  pyloric 
valve's  closing-stimulus,  the  shorter  the  time  the  food  remains  in  the 
stomach. 

4.  Another  gastric  function  (Volhard)  is  probably  the  saponification  of 
emulsified  fats.     The  importance  of  this  activity  is  as  yet  unknown. 

5.  A  fifth  function  of  the  organ  is  to  coagulate  the  caseinogen  of  milk 
into  casein  and  possibly  to  start  it  toward  digestion  by  this  change.  The 
enzyme  rennin  does  this  and  besides,  as  has  been  said,  may  give  the 
stomach  still  other  functions  as  yet  unsuspected. 

6.  A  sixth  action  in  digestion  is  the  sterilization  of  food  containing 
bacteria,  the  free  mineral-acid  present  in  the  gastric  juice  in  amount  of 
1  per  cent.,  more  or  less,  being  the  chief  agent  in  this  direction. 

7.  The  long-continuance  of  the  food  in  the  relatively  insensitive 
stomach  adapts  the  chyme  in  temperature  for  the  best  digestion  and  pre- 
vents injury  or  at  least  functional  interference  with  the  duodenal  glands 
and  muscles  by  chyme  either  too  hot  or  too  cold.  This  use  depends 
directly  on  the  first  function  noted — that  the  stomach  is  a  reservoir.    As 


196 


DIGESTION 


such  it  warms  food  too  cold  and  cools  food,  usually  liquids,  taken  too 
hot  for  the  duodenum  to  bear  well. 

8.  Another  function  similar  to  the  last  in  its  usefulness  is  the  lique- 
faction of  the  food  before  its  entrance  to  the  gut  proper,  thus  avoiding 
irritation  and  more  or  less  injury.  This  process  is  a  combination  of 
chemical,  mechanical,  thermal,  and  secretory  agencies. 

Fig.  93 


Section  through  the  antrum-wall  of  the  dog:  Z,  villi;  LD.,  Lieberkuhn's  glands  (Brunner's  glands 
are  in  the  submucosa,  Subm.);  MM,  muscularis  niucosa?;  Muse.  R.,  transverse,  and  Muse.  L., 
longitudinal  section  of  the  muscularis.  The  veins  are  shown  black,  the  arteries  cross-striated. 
**/l.      (Mall.) 

9.  Another  function  is  to  invert  sugars  by  means  of  its  acid,  whether 
the  former  are  introduced  into  the  stomach  as  such  or  are  produced 
there  by  the  hydrolysis  of  starch. 

10.  A  tenth  usefulness  of  the  stomach  is  a  slight  degree  of  absorption. 
The  materials  absorbed  are  chiefly  alcoholic  solutions,  alkaloids,  salines, 
and  possibly  a  very  small  amount  of  water  and  of  hydrolyzed  or  soluble 
proteids. 


DIGESTION 


197 


Yet,  with  all  these  functions  regularly  performed  by  the  normal  stomach 
people  live  stomachless  with  a  tolerable  degree  of  comfort. 


Fig.  94 


Longitudinal  section  of  the  pyloric  region:  P,  the  pylorus;   D,  duodenum;   C.P.,  pyloric 
canal;    V.P.,  pyloric  vestibule.      (E.  Muller.) 

The  Small  Intestine. — The  small  intestine  is  a  tube  about  650  cm.  long 
and  somewhat  larger  at  the  upper  end  than  at  the  lower.  It  has  practically 
the  same  coats  as  the  stomach.  Exner  and  Bienenfeld  suppose  that  the 
so-called  muscularis  mucosfe  has  for  its  function  to  prevent  the  puncture 


Fig.  95 


The  two  lymph-plexuses  in  the  wall  of  the  dog's  stomach  between  which  the  muscularis 
mucosae  lies.      ^^/\-      (Mall.) 

of  the  gut  by  bones  and  other  sharp  objects.  The  mucous  membrane  is 
made  up  of  various  secreting  glands,  of  lymph-nodules,  and  of  the  villi 
which  extend  inward  from  it.  One  set  of  glands  called  the  duodenal 
(or  Briinner's  glands)  appear  to  the  eye  to  be  almost  identical  with  those 


198 


DIGESTIOX 


in  the  fundus  of  stomach.  Their  function  must  be  different,  however, 
for  no  pepsin  is  formed  in  the  duodenum;  enterokinase,  for  example, 
is,  however.  These  are  largest  in  the  upper  part  of  the  duodenum, 
but  are  not  found  below  the  first  portion  of  the  jejunum  (simple  folhcles). 
The  crypts  of  Lieberkiihn  are  simple  glands  in  the  mucosa  between  the 
bases  of  the  ^^lli.  Scattered  among  these  are  the  goblet-cells,  producing 
mucus;  what  else  they  secrete  is  still  unknown.  The  valvulse  con- 
niventes  are  prominent  acute  ridges  running  part  way  around  the  interior 
of  the  gut-wall.  Their  use  is  apparently  to  many  times  increase  the 
secretive  and  absorptive  surface  of  the  intestine  and  also  to  retard  the 
downward  passage  of  the  chyle.  Some  of  these  are  nearly  a  centimeter 
in  height.     The  villi  are  minute  finger-like  projections  into  the  lumen 

Fig.  96 


m 


Goblet-cells  from  the  gut  of  geotriton,  to  show  the  different  functional  conditions  of  this  sort 
of  epithelium.  In  the  first,  a  secretory  act  has  just  ended  and  a  second  is  beginning.  In  the 
second  and  third  and  fourth  cells  various  stages  of  activity  are  shown,  both  in  the  cytoplasm 
and  in  the  nucleus.      (Galeotti.) 


of  the  small  intestine.  They  are  largest  and  most  numerous  in  the 
duodenum  and  jejunum.  Krause  estimates  their  number  at  about 
4,0f)0/)00,  and  they  are  from  0.5  to  3.0  mm.  in  length.  From 
without  inward  a  villus  is  compo.sed  of  striped  columnar  epithelium, 
with  goblet-cells  scattered  here  and  there  through  it.  Beneath  this 
is  the  membrane,  then  comes  the  reticular  adenoid  tissue,  containing 
lymph-corpuscles,  bloodvessels,  and  nerves  in  abundance.  There  are 
also  numerous  smooth  muscle  fibers,  especially  about  the  large  lymphatic 
ves.se]  in  the  midrllc  of  the  villus.  The  lyniph-uodules  of  the  gut-wall 
are  most  numerous  in  the  lower  half  of  the  ileum,  where  there  are  no 
valvulee  conniventes,  especially  in  the  ileum.  These  combine  in  masses 
to  form  Fever's  patches,  which  are  from  1  to  10  cm.  long. 

The  nerve-supply  of  the  small  intestine  comes  from  the  spinal  cord 


DIGESTION 


199 


Fi<:.  97 


by  way  of  the  sympathetic  chain,  the  great  and  small  splanchnics,  the 
solar  and  mesenteric  plexuses,  and  especially  from  the  vagus. 

The  movements  of  the  small  intestine,  for  descriptive  purposes 
only,  may  be  analyzed  into  four  varieties.  These  are  peristalsis,  longi- 
tudinal contractions,  swinging  movements,  and,  according  to  Cannon, 
"segmentation."  The  three  first-mentioned  are  but  aspects  of  one 
complex  movement;  the  last  is  more  or  less  separate,  and  as  described  by 
Cannon,  only  recently  discovered. 

Intestinal  peristalsis,  like  peristalsis 
elsewhere  (esophagus,  ureter,  etc.), 
is  a  slow  progressive  contraction  of 
the  circular  muscular  fibers  forming 
the  major  part  of  the  musculature  of 
the  gut.  This  successive  contraction 
of  the  rings  of  muscle  causes  a  pro- 
gressive narrowing  of  the  lumen  of 
the  tube — a  process  well  adapted  to 
squeezing  its  contents  slowly  along. 
The  progression  is  much  aided  by  the 
automatic  contraction  of  the  fibers 
above  a  mass  of  food,  while  those 
below  it  are  simultaneously  relaxed 
(Bayliss  and  Starling).  The  rate  of 
movement  is  slow.  In  one  case  a 
marble  was  pushed  along  only  a  trifle 
more  than  1  cm.  in  a  minute,  but  the 
normal  propulsion  of  the  chyle  is 
doubtless  often  at  a  much  greater 
rate.  There  is  no  direct  evidence 
that  antiperistalsis  normally  occurs 
in  the  small  intestine,  although  it 
does  occur  in  the  large.  It  probably 
takes  place,  however,  in  certain  ab- 
normal conditions,  and  in  the  small 
Crustacea  (for  example,  Daphnia) 
antiperistalsis  is  the  normal  direction 
of  the  wave. 

Lessening  of  the  length  of  the 
gut  by  means  of   contraction  of  the 

longitudinal  fibers  is  an  almost  indispensable  part  of  the  peristaltic 
movements,  for  by  this  means  the  intestinal  tul)e  is  drawn  over  the 
contained  mass,  so  leaving  the  latter,  as  it  were,  farther  down  the  intestine 
than  before.  Thus,  peristalsis  and  occasional  shortening  of  a  loop  of  the 
intestine  together  squeeze  the  contained  mass  slowly  along.  The  speed 
of  these  movements  is  hastene^l  several  times  when  the  intestines  are 
exposed  to  the  irritating  air,  as  during  an  operation  or  a  demonstration. 
Normally  they  are  very  slow — a  gentle  complex  squirming  movement 
hard  to  describe  but  easv  to  understand. 


Magnification  of  the  intestinal  area  by 
the  viih.  Were  the  villi  not  present  the 
absorptive  area  of  the  gut  would  be  only 
about  one-nineteenth  of  what  it  is.  This 
ratio  is  that  of  the  smaller  rpctangle  to  the 
larger. 


200 


DIGESTION 


The  swingijig  motions  of  the  intestine  depend  on  the  manner  in  which 
loops  of  the  gut  are  fastened  posteriorly  by  the  omentum.  They  are 
produced  by  contraction  of  both  the  circular  and  the  longitudinal  mus- 
cular fibers  acting  together,  and  occur  every  five  or  six  seconds.  They 
are  not  influenced  by  nerves,  but  they  are  by  temperature  (Ludwig). 


Diagram  of  tlie  intestinal  movements:    the  solid  lines  show  one  phase  of  the  movement, 
and  the  dotted  lines  the  other  phase. 

By  the  aid  of  this  complex  movement  fa  combination  of  peristalsis, 
shortening,  and  swinging),  the  first  portion  of  an  ordinary  meal  reaches 
the  cecum  in  about  three  hours,  on  an  average,  and  it  is  at  least  six 
hours  more  before  the  last  part  of  such  a  meal  passes  through  the 
ileocecal  valve.     Thus,  a  bit  of  food  recjuires  three  hours  to  pass  the 


DIGESTION 


201 


575  cm.  or  so  of  the  small  intestine,  and  an  average  meal  remains  within 
at  least  six  hours  and  often  twice  as  long  if  we  include  the  stay  in  the 
stomach. 

The  process  of  "rhyiJimic  segmeniaiion^'  is  well  denoted  by  its  name, 
due  to  Cannon,  who  described  it  from  the  shadows  cast  by  the  digesting 
intestine  of  the  cat,  dog,  rat,  and  rabbit.  Bismuth  subnitrate  having 
first  been  mixed  with  the  animals'  meals,  the  chyle  was  sufficiently  opaque 
to  the  Rontgen  rays,  so  that  its  position  and  condition  as  regards  seg- 
mentation, etc.,  could  be  seen  on  the  fluorescent  screen.  A  cat  con- 
tentedly digesting  a  meal  could  thus  be  studied  and  watched  for  hours 
under  more  or  less  normal  conditions.  Suppose  a  "string"  of  chyle 
10  cm.  long  contained  in  a  loop  of  the  animal's  intestine.  Suddenly,  by 
the  simultaneous  quick  constriction  of   the  gut  in  five  or  six  places, 

Fig.    99 


Lymphatic  and  Auerbach's  plexuses  in  the  intestine's  muscular  coat:  n,  the  nerv-e  plexus; 
I,  the  lymphatic  plexus.      (Auerbach.) 

this  string-like  mass  of  food  is  cut  into  as  many  separate  pieces.  Two 
seconds  later  (in  the  cat),  by  intestinal  constrictions  midway  between 
those  which  occurred  before,  these  five  or  six  pieces  are  again  divided 
each  in  the  middle  and  the  halves  pushed  aside  and  united  again  into 
five  or  six  new  pieces.  Two  seconds  later  constrictions  occur  where 
they  occurred  four  seconds  before,  thus  segmenting  the  food-mass  once 
more  as  it  was  at  that  time.  Thus,  the  alternate  division  and  uniting  and 
redivision  and  reuniting  goes  on  thirty  times  a  minute  (in  case  of  the  cat), 
perhaps  for  half  an  hour  or  more.  The  string  of  chyle  meanwhile  does 
not  advance  along  the  cat's  intestine,  but  remains  to  be  chopped  up  by 
this  process  of  the  gut's  circular  muscular  fibers.  Wolfl'  corroborates 
more  or  less  fully  these  results  obtained  by  Cannon.  He  thinks  the  gut's 
movements  are  not  continuous  with  those  of  the  antrum,  but  originate  at 
a  point  farther  down  the  intestine.     In  man,  probably  the  rhythm,  if  it 


202 


DIGESTION 


occur  at  all,  is  much  slower,  for  in  the  dog  the  movement  is  said  to  occur 
twenty  times  a  minute  only,  while  in  the  rat  the  segmentation  takes  place 
every  second,  rhythmic  movements  being  generally  more  rapid  the  smaller 
the  mammal.  By  this  supposed  rhythmic  segmentation,  occurring  prob- 
ablv  in  many  places  in  the  gut  at  the  same  time,  the  food-mass  may  be 
thoroughly  mixed  with  the  juices  of  the  intestine  and  any  lumps  remain- 
ing in  it  reduced.  ^Moreover,  by  this  means,  if  they  obtain,  the  portion 
of  the  chyle  which  is  hydrolyzed  and  ready  for  absorption  is  squeezed 
strongly  against  the  absorbing  organs,  the  villi  thus  furnishing  a  strong 
pressure  inward  several  times  a  minute.  This  pumping-action  w^ould 
doubtless  assist  the  capillary  circulation  of  the  villi  and  make  them  in 

Fig.   100 


^y.m.s 


The  innervation  of  the  gut  (dog):  png,  vagus;  pi.  cae,  celiac  plexus;  gg.  m.s,  superior  mesenteric 
ganglion;  gg.m.i,  inferior  mesenteric  ganglion;  PL  hyp,  hypogastric  plexus;  gap,  great  splanchnic; 
n.er,  erector  nerve;  i»xni,  thirteenth  dorsal  pair;  Lm,  third  lumbar  pair;  S^,  first  sacral  pair. 
(Morat.) 

general  much  more  active  in  all  their  functions  than  else  they  could  be. 
Further  confirmation  of  this  matter,  however,  is  required  before  it  is 
generally  accepted  as  above  described  as  a  normal  and  universal  fact 
in  human  digestion. 

The  innervaiion  of  the  small  intestine  is  still  a  matter  of  discussion  so 
far  as  specific  neural  functions  are  concerned.  Most  observers  deem  the 
vagus  the  motor  or  actuating  nerve  of  the  gut.  In  the  dog,  at  least,  there 
is  some  evirlcnce  that  the  vagus  contains  also  inhibitory  fibers,  perhaps, 
however,  coming  indirectly  from  a  special  place  fJaCobi).  Pfliiger  first 
claimed  that  tin-  sympatlictic  was  the  inhibitory  nerve  of  the  intestine, 
and  tlie  opinion  is  being  continually  supported  hy  researches.     Mayer 


DIGESTION 

Fig.  101 


203 


Meissncr's  Ple.nis. 
The  sjinpathetic  nerve-fabric  as  seen  in  and  be'ow  the  intestinal  villi.      (Ramon  y  Cajal.) 


and  von  Basch  ascribe  it,  however,  to 
the  vaso-constrictor  action  of  these 
nerves,  but  it  has  been  shown  that 
the  action  is  inhibitory  after  the  cir- 
culation has  ceased.  According  to 
Ehrmann,  the  sympathetic  (splanch- 
nics)  are  inhibitory  to  the  circular 
fibers,  but  motor  to  the  longitudinal 
fibers  of  the  intestinal  muscle.  Re- 
searches by  Magnus  indicate  that 
Auerbach's  plexus  controls  the  move- 
ments of  the  circular  muscular  fibers 
and  has  nothing  to  do  with  the  longi- 
tudinal movements.  Removal  of 
Meissner's  plexus  did  not  aft'ect  the 
peristalsis  in  an  isolated  loop  of  the 
gut.  A  center  for  the  movements 
has  been  located  by  von  Bechterew 
and  Mislawski  in  the  sigmoid  gyrus, 
and  this  must  be  in  close  relation 
w^ith  the  centers  which  are  concerned 


Fig.  102 


Meissner's  plexus  in  the  submucous  layer 
of  the  gut :  a,  ganglia;  6,  cords  of  the  plexus; 
c,  small  bloodvessel.      (Cadiat.) 


204  DIGESTION 

with  the  emotions,  for  the  intestinal  movements  are  easily  disturbed. 
Other  centers,  actuating  and  inhibitory,  probably  are  placed  in  the  cord, 
the  spinal  ganglia,  or  in  the  great  abdominal  plexuses.  Despite  all  these 
diverse  facts,  the  probability  is  continually  confirmed  that  the  control 
of  the  whole  alimentary  canal  is  of  the  simplest  sort  through  the  nerve- 
net  in  its  walls.  Its  neuro-muscular  mechanism  is  doubtless  a  highly 
unified  structure,  whose  details  remain,  however,  to  be  described. 

Pancreatic  juice  is  poured  out,  mixed  with  the  bile,  into  the  upper 
portion  of  the  duodenum;  there  it  mixes  with  the  intestinal  juice  proper, 
forming  altogether  a  very  complex  digestive  liquid.  The  external  secre- 
tion of  the  pancreas  is  in  difi'erent  animals  and  at  dift'erent  times  a 
very  variable  substance.  From  a  dog's  temporary  fistula  its  specific 
gra\dty  is  about  1030;  it  is  clear,  but  of  a  syrupy  consistence,  becoming 
still  more  viscid  on  cooling;  at  75°  or  at  0°  it  coagulates.  It  is  alkaline 
in  reaction,  due  probably  to  salts  of  sodium.  It  is  rich  in  proteid.  A 
sample  analyzed  by  C.  Schmidt  contained  900.8  parts  water  and  99.2 
parts  of  solid  material,  of  which  90.4  parts  were  organic  matter  and  8.8 
parts  ash.  This  ash  was  mostly  sodium  chloride,  but  contained  also 
sodium  oxide,  potassium  chloride,  trisodic  phosphate,  lime,  magnesia, 
earthy-phosphates,  and  iron.  Its  daily  amount  in  man  is  perhaps  175 
grams. 

Pancreatic  juice  contains  probably  at  least  five  enzymes:  tr}^sinogen, 
hvdrolyzing  proteid;  diastase  (amylopsin),  hydrolyzing  carbohydrates; 
lipase  (steapsin),  saponifying  and  indirectly  emulsifying  fats;  probably 
rennin,  coagulating  caseinogen;  and  perhaps  lactase  and  invertase. 

According  to  Bayliss  and  Starling,  no  tr^'psin  is  contained  in  fresh 
pancreatic  juice,  but  the  tr}'psinogen  there  found  is  changed  to  tr^-psin 
when  it  arrives  in  the  intestine  by  the  action  of  enterokinase  (kinase), 
secreted  by  the  upper  end  of  the  gut.  By  means  of  erepsin  from  the  intes- 
tinal wall  probably  the  peptone  produced  by  hydrolysis  is  split  still 
farther  into  the  amido-acids. 

Proteid. 

Albumoses. 

1 
Peptone. 


Mixture  of  many  amido-acids  having  Tyrosin,  tryptophan,  cystin,  alanin, 

complicated  connections — the  substances         amido-valerianic  acid,  leucin,   aspara- 
known  as  polypeptide.  ginic   acid,    glutaminic   acid,    histidin, 

lysin,  arginin.     (Abdcrhalden.) 

Inasmuch  as  Lowi,  and  others  after  him,  have  been  able  to  keep  dogs 
nourished  by  feeding  them,  for  nitrogenous  food,  these  amido-acid  sub- 
stances Heucin,  tyrosin,  arginin,  asj)artic  acid,  etc.),  considered  the  end- 
products  of  tr\-ptic  proteolysis,  it  is  now  suspecterl  by  many  that  the  albu- 
moses and  some  albumins  are  synthetic  j)roducts  of  the  action  of  an 


DIGESTION 
Fig.  103 


205 


^■^^^^^A^^s^^ 


Section  of  pancreas:      a,  alveolus;   6,  connective  tissue;   c,  lobule;  d,  interlobular 
connective  tissue;   e,  island  of  Langerhans.      (Bates.) 


Fig.   104 


Stenpsin,  lipase. 
^^  Secretin. 
Rennin. 
Trypsin. 

Islands  of  Langerhans. 
Amylopsin. 
Enterokinase. 


Functions  of  the  pancreas.      The  arrows  indicate  the  respective  secretions  of  the  organ, 
their  origins  and  their  destinations. 


206  DIGESTION 

unknown  substance  secreted  by  the  intestinal  wall,  the  materials  being 
these  amido-acids.  This  synthesis  may  occur  as  the  amido-bodies  are 
absorbed  through  the  protoplasm  of  the  epithelium,  or  by  other  agency 
elsewhere.  The  theories  of  proteolysis  have  already  been  given  in 
discussing  the  action  of  pepsin. 

The  action  of  the  diastase  (amylopsin)  is  not  unlike  that  of  ptyalin 
described  above  (page  188),  but  it  is  more  vigorous,  and  it  has  the  power 
of  dissolving  the  cellulose  covering  of  starch  grains,  thus  allowing  it  to 
digest  many  uncooked  vegetables  and  fruits  more  or  less  indigestible  by 
saliva  in  its  usual  environment.  It  is  doubtful  if  the  diastatic  amylopsin 
converts  all  the  dextrin  formed  to  maltose,  this  likely  enough  being  in 
part  a  product  of  the  synthesizing  action  of  an  enzyme  in  the  absorptive 
mechanism  of  the  gut-wall. 

The  action  of  pancreatic  juice  on  fats  by  means  of  its  lipase  (steapsin) 
like  some  of  its  other  functions,  has  probably  a  precedent  in  the  stomach 
of  perhaps  much  smaller  importance.  This  enzyme  is  a  very  unstable 
one,  and  has  not  been  isolated  in  even  approximate  purity.  Loevenhart 
has  recently  claimed  to  have  found  evidence  that  lipase  exists  in  all  the 
tissues,  especially  in  the  liver,  milk,  blood,  lymph,  and  intestinal  juice, 
and  he  supposes  that  the  tissue-fats  (stearin,  olein,  and  palmitin)  are 
built  up  in  the  tissue-cells  through  its  agency  from  free  fatty  acids  cir- 
culating in  the  blood  and  lymph  as  soaps.  In  general,  it  has  been  pre- 
sumed that  the  action  of  lipase  was  the  usual  one  of  hydrolysis  followed 
immediately  by  cleavage  into  a  glycerin  and  the  fatty  acid.  Thus,  in  case 
of  the  triglyceride  palmitin  the  reaction  would  be — 

C3H5(OC,5H3,CO)3  +  3H.,0  =  SC.sHgiCOOH  +  C3H5(OH)3 

Palmitin.  Water.         Palmitic  acid.  Glycerin. 

the  acid  then  uniting  with  potassium,  sodium,  or  calcium  either  in  the 
gut-wall  or  in  the  tissues  to  produce  the  corresponding  soap.  This  in  a 
nut-shell  is  the  important  process  of  safonifi cation,  carried  on  by  steapsin. 
In  addition,  the  lipase  indirectly  emulsifies  fats,  this  being  a  mechanical 
process  (chemically  performed  by  the  fatty  acids),  while  the  other  is  a 
distincdy  chemical  process.  The  exact  relation  of  these  two  processes 
has  not  even  yet  been  well  determined.  Especially  is  it  in  doubt  whether 
all  the  fat  destined  for  food  is  saponified  or  whether  some  of  it  is  emulsi- 
fied only  and  direcdy  absorbed.  For  the  most  part  emulsification  is 
probably  due  to  the  action  of  the  fatty  acids  formed  by  saponification,  so 
that  very  Hkely  both  j)rocesses  go  on  side  by  side  in  the  duodenum.  In 
this  process  the  Inle,  poured  into  the  gut  with  the  pancreatic  juice,  plays 
an  important  part.  It  probably  aids  saponification  by  means  of  its 
cholic  acid.  Furth(  rinore,  the  action  of  lipase  (steapsin)  is  at  its  best  in 
the  presence  of  bile  phis  hydrochloric  acid,  according  to  Rachford,  so 
that  the  reagents  on  fat  in  the  (hiodenum  are  very  complex  and  the 
reactions  correspondingly  complicated.  The  actions  of  the  supposed 
milk-curdling  (rennin)  and  sugar-inverting  enzymes   (maltase,  etc.)  of 


DIGESTION  207 

the  pancreatic  external  secretion  need  no  special  description;  indeed, 
little  that  is  definite  and  certain  could  be  said  about  them. 

Intestinal  juice,  or  succus  entericus,  as  it  used  to  be  called,  is  even 
less  known  than  is  pancreatic  juice  because  it  is  secreted  in  very  small 
quantity  and  becomes  immediately  mixed  with  the  complex  liquid  com- 
poimded  by  the  salivary  glands,  the  stomach,  the  liver,  and  the  pancreas. 
This  juice  is  opalescent,  straw-colored,  strongly  alkaline,  with  a  specific 
gravity  of  about  1010,  and  contains  much  proteid,  mucin,  carbonate, 
and  lactate.  It  is  produced  by  the  simple  follicles,  crypts  of  Lie})erkuhn 
of  the  small  intestine,  and  perhaps  in  part  also  by  Brunner's  glands. 
The  function  of  the  intestinal  juice  appears  to  be  to  hydrolyze  carbohy- 
drates, to  finish  the  hydrolysis  of  protein,  and  to  invert  sugars.  It  probably 
puts  the  finishing  touches  to  the  hydrolysis  of  carbohydrates  preparatory 
to  inverting  them  as  they  pass  through  the  intestinal  wall  during  absorp- 
tion. As  inverting  enzymes,  invertase  (inverting  saccharose  to  dextrose) 
and  maltase  (inverting  maltose  to  dextrose)  have  been  named.  The 
proteolytic   ferment    present,    according   to    Abderhalden,   is    erepsin. 

Fig.  105 


Section  in  the  bottom  end  of  a  tubular  gland  of  a  dog's  duodenum:    a,  b,  c,  "protoplasmic" 
cells;   d,  e,  mucous  cells.      (Bizzozero.) 

^Tiether  the  enzyme  enterokinase,  described  by  Bayliss  and  Starling  as  of 
such  great  importance  for  stimulating  in  union  with  secretin  the  pan- 
creatic glands,  is  produced  by  the  simple  follicles  or  by  Brunner's  glands 
is  unrlecided.  Delezenne  thinks  it  is  secreted  by  the  lymph-follicles,  and 
Camus  supposes  that  it  is  confined  to  the  gut's  lumen,  while,  on  the  other 
hand,  the  non-enzymic  secretin  may  go  directly  into  the  blood-stream. 
In  either  event  enterokinase  w^ould  form  a  part  of  the  intestinal  juice, 
and  in  its  supposed  function  of  developing  tripsinogen  into  tr^'psin 
would  have  considerable  importance. 

Bile  has  some  proper  influence  on  the  intestinal  digestion  of  fats 
as  has  been  just  suggested  above,  but  the  action,  although  perhaps 
important,  is  none  too  well  understood. 


20S 


DIGESTION 


The  Large  Intestine. — The  large  intestine  in  structure  is  like  the  small 
intestine,  but  it  is  larger  in  diameter  and  shorter,  being  about  150  cm. 


Fig.  106 


Hepatic  cell-cords:  a,  a  cell;   b,  a  lymph-space.      (Bates.) 
Fig.  107 


^  Urea. 
^-  Glycogen. 

Bile-salts. 

Bile-pigments. 

Secretin. 


Functions  of  the  liver.      The  arrow.-  indicate  (he  rcsportive  secrctifms,  internal  and  external, 
of  this  complex  gland,  their  place.s  of  origin,  and  their  destination.-. 

long.     The  longitudinal  mu.scular  coat  is  much  less  complete  than  in  the 
small  intestine;  in  the  rectum  the  circular  coat  is  very  thick.     There 


DIGESTION 


209 


are  no  villi  and  no  Briinner's  glands,  but  the  simple  follicles  (crypts  of 
Lieberkiihn)  are  both  more  numerous  and  larger  than  in  the  small 
intestine.  Much  mucus  is  secreted  by  the  wall  of  this  part  of  the 
intestine,  but  no  enzymes  have  been  isolated  from  its  secretory 
product.  The  ileo-cecal  valve  guards  the  opening  between  the  small  and 
the  large  intestines.  It  consists  of  two  folds  of  mucous  membrane  with 
muscular  fibers,  projecting  into  the  large  intestine.    The  mucosa  of  the 


Diagram  suggesting  the  functions  of  the  liver.  Parts  of  three  hepatic  cells  are  shown :'P. T". , 
portal  veins;  H.A.,  hepatic  arteries;  fi.C.bile  capillary  with  its  rootlets  rising  in  the  cytoplasm. 
The  arrows  suggest  some  of  the  relations  and  movements  of  the  various  substances. 


rectum  is  thicker  and  more  vascular  than  that  of  other  parts  of  the  gut. 
It  has  three  or  four  large  permanent  folds  of  a  semilunar  shape.  The 
lower  portion  of  the  rectum  has  two  sphincters,  made  of  tough  bands  of 
circular  muscle-fibers,  the  former  being  supported  by  the  levatores  ani 
muscles.  The  nerve-supply  of  this  part  of  the  gut  comes  from  two 
sources,  from  the  upper  lumbar  roots  (sympathetic),  and  from  the  lower 
mesenteric  ganglion,  the  hypogastric  plexus,  the  vagus,  and  the  sacral 
14 


210 


DIGESTION 


roots.  According  to  Fellner,  the  sacral  nerves  are  motor  for  the  rectal 
longitudinal  muscle  fibers,  and  inhibitory  for  the  circular  fibers,  while 
the  hypogastric  influence  is  contractile  for  the  circular  fibers  and  relaxa- 
tive  to  the  longitudinal  fibers  (the  so-called  "crossed  innervation"). 
Winkler  claims  that  the  hypogastric  is  the  proper  motor  nerve  of  the 
whole  large  intestine.  The  vagus  is  probably  both  motor  and  inhibitory. 
The  iMOVEMEXTS  OF  THE  LAKGE  INTESTINE  are  Icss  Complicated 
than  are  those  of  the  small  gut.  According  to  Cannon,  the  chief  move- 
ment of  the  descending  colon  is  the  very  slow  peristalsis  produced  by 
the  progressive  tonic  contraction  of  the  circular  fibers.  In  the  remainder 
of  the  large  gut,  in  man  the  ascending  and  transverse  colon  and  the 
cecum,  the  chief  movement  and  themost  common  one  is  anti  peristalsis. 


Fig.  109 


Fig.  110 


The  ileo-cecal  valve  as  seen  on  cutting  away 
a  part  of  the  cecum:  1,  ileum;  2,  cecum;  3, 
ascending  colon;  4,  venniform  appendix;  5, 
opening  into  the  same;  6,  inferior  lip;  7,  superior 
lip;  8,  aperture  of  the  valve;  9,  its  retinaculum. 
'/2.      (Rauber.) 


Cells  of  a  frog's  liver  (injected  with  sodium 
Bulphindigotate),  to  show  how  the  bile-channels 
begin.      (Kupffer.) 

The  result  of  this  backward  per- 
istaltic movement  is  to  keep  the 
lifjuid  chyle,  coming  continually 
into  the  colon  from  the  ileum,  a 
long  time  in  the  cecum  and  to  pre- 
vent its  being  pushed  onward 
into  the  rectum  before  absorp- 
tion of  its  li(iuid  has  had  time  to  take  place.  Each  period  of  anti- 
peristalsis  (in  the  cat)  lasts  from  two  to  eight  minutes,  and  the  periods 
recur  at  intervals  of  from  ten  to  twenty  minutes.  Rhythmic  pulsating 
or  .segmenting  movements  are  of  rare  occurrence  in  the  large  gut  of  the 
cat,  but  were  seen  once  or  twice;  tonic  constrictions  seem  to  occur  at 
intervals  along  the  colon  when  the  latter  is  filled,  and  these  t(>nd  to  press 
the  contents  toward  the  rectum.  Bayliss  and  Starling  corroborate 
Cannon's  observation  that  it  is  the  distention  of  the  colon  with  chyle 
that  actuates  the  movements  of  the  tube. 


DIGESTION  21 1 

The  ileo-cecal  valve  seems  to  be  quite  competent  for  preventing  the 
backward  passage  of  soUd  matters,  that  is,  into  the  ileum,  but  it  readily 
allows  liquids  to  pass  in  this  direction.  It  is  possible  then  to  inject  nutrient 
enemata  into  the  small  intestine.  Katz  and  Winkles  find  that  stimulation 
of  the  vagus  closes  the  valve,  and  that  the  splanchnics  influence  it  to 
open;  stimulation  of  the  In-pogastrics  seemed  to  have  no  effect.  (See 
Absorption,  p.  210.) 

Defecation  is  the  process  by  which  the  useless  residue  of  the  chyle  is 
periodically  voided  from  the  gut.  In  the  human  animal  the  process 
occurs  usually  once  a  day,  most  easily  just  after  the  first  meal,  the  neural 
mechanism  being  then  stimulated  by  the  processes  in  the  upper  end  of  the 
alimentary  canal.  In  many  cases,  however,  defecation  takes  place  twice 
daily,  and  in  a  much  smaller  proportion  of  persons  only  every  other  day. 
Defecation  is  a  complicated  reflex  act  voluntarily  started  and  inhibitable 
at  any  stage.  The  outer,  lower  sphincter  and  the  levatores  ani  muscles 
supporting  the  internal  sphincter  are  made  of  cross-striated  fibers.  The 
internal  sphincter  and  the  strong  circular  fibers  of  the  rectal  wall  and  of 
the  sigmoid  flexure  are  of  "unstriated"  or  smooth  muscular  tissue.  It  is 
probable,  however,  that  the  fibers  of  the  external  sphincter  are  made  of 
neither  typically  skeletal  nor  smooth  muscle,  for  they  are  unaffected 
by  curare,  and,  as  Goltz  and  Ewald  have  shown  on  dogs,  destruction  of  the 
cord  which  causes  atrophy  of  the  skeletal  muscles  leaves  the  external 
sphincter  unaffected. 

The  two  sphincters  are  normally  in  a  state  of  tonus  dependent  on 
their  connection  with  the  central  nervous  system,  a  tonus  that  is  not 
destroyed  by  curare. 

When  defecation  is  to  take  place,  the  diaphragm  is  first  made  rigid  in 
contraction,  and  the  glottis  is  shut.  The  abdominal  muscles  then  unite 
in  forcible  expiratory  contraction,  and,  the  perineal  muscles  and  the 
sphincters  being  relaxed,  feces  are  forced  out  of  the  sigmoid  flexure 
(their  habitual  reservoir  normally)  into  and  through  the  rectum  and  out 
at  the  anus.  Powerful  contraction  of  the  levatores  ani  serve,  finally,  to 
empty  the  lower  end  of  the  rectum  betw^een  the  two  sphincters,  which 
then  at  once  recover  their  normal  closure-tonus.  The  nerve-center 
coordinating  the  various  movements  of  defecation  is  not  as  yet  certainly 
known,  although  Frank-Hochwart  has  recently  found  much  evidence 
that  in  dogs  at  least  it  is  often  to  be  demonstrated  in  the  posterior  end 
of  the  posterior  central  gyrus  of  the  brain,  in  apes  called  "Sherrington's 
center."  There  are  probably  subsidiary  centers  in  the  lumbar  cord  or 
in  the  ganglia  of  the  pelvis.  Defecation  is  an  excellent  example  of  a 
process  once  wholly  reflex  (distention  of  the  sigmoid  flexure  or  irritation 
of  upper  end  of  rectum  furnishing  the  afferent  impulses),  which  has 
become  more  or  less  under  the  will's  control  in  man  and  in  some  of  the 
lower  animals  long  associated  with  him.  In  infants  and  in  most  brutes 
the  process  is  still  wholly  involuntary  and  largely  reflex,  as  it  is  also  in 
manv  conditions  of  nervous  disease. 


212  DIGESTION 

Digestion  in  the  Large  Intestine. — The  chief  function  of  the 
large  intestine  is  undoubtedly  absorption,  especially  of  water,  and  as  a 
reservoir  for  the  ever-accumulating  chyle.  It  is  likely,  however,  that  the 
uses  of  this  part  of  the  gut  are  more  numerous  than  this,  its  hydrolysis 
of  proteid,  for  example,  being  perhaps  of  consequence.  It  has  long  been 
known  that  in  diseased  conditions  of  the  stomach,  etc.,  a  person  may  be 
kept  alive  a  long  time  by  enemata  of,  for  example,  a  solution  of  the  whites 
of  eggs  in  water,  and  even  when  introduced  in  far  too  small  amount  to 
reach  the  ileum  or  jejunum.  Berlatsky,  working  in  Pawlow's  laboratory, 
finds  that  the  large  intestine  not  only  absorbs  proteid,  but  that  it  digests 
it.  Milk  especially,  he  thinks,  may  be  digested  in  this  part  of  the  intestine, 
the  reaction  there  being  regularly  alkaline.  Comparatively  little  research 
has  been  done  on  zymolysis  in  the  colon. 

Bacteria  seem  to  have  a  part  normally  in  digestive  processes  in  the 
intestine,  although  their  influence  is  possibly  more  helpful  in  absorption 
than  in  digestion  proper.  In  the  small  intestine  the  bacteria  are  relatively 
few,  but  within  a  day  after  birth  multitudes  of  them  have  developed  in  the 
colon  and  rectum,  and  they  continue  there  through  life.  Their  food  is  the 
various  organic  substances  found  in  the  feces  (see  page  252),  especially 
the  undigested  bits  of  proteid  and  carbohydrate  food  and  cellulose. 
The  changes  produced  in  the  proteids  by  the  bacteria  are  those  of  putre- 
faction; the  end-products  are  the  (odorous)  substances  indol,  skatol,  etc. 
The  sugars  and  starches  are  promptly  broken  up,  and  cellulose  with  the 
liberation  of  methane  (Moore),  but  in  what  manner  is  not  well  under- 
stood. 

It  is  not  obvious  then  what  benefit  the  colonic  bacteria  are  to  their 
host,  and  it  is  possible  that  to  be  without  them  would  be  advantageous. 
Indeed,  Arloing  has  shown  that  mucin  and  mucus  are  destructive  of  all 
microorganisms,  even  the  most  resistant  if  time  enough  be  given.  This 
then  is  probably  the  chief  function  of  the  mucus  of  the  alimentary  canal 
(especially  abundant  in  the  colon):  to  destroy  the  bacteria  or  some  of 
them,  or  to  lessen  their  activity.  The  well-known  work  of  Nuttall  and 
Thierfelder  on  guinea-pigs  has  shown  that  these  young  animals  thrive 
for  eight  days  after  birth  at  least  with  no  bacteria  in  them.  Other 
researchers  suppose,  however,  that  this  period  is  too  short  to  be  indicative, 
and  that  most  animals  at  least  do  not  grow  to  maturity  without  aid  from 
the  mysterious  action  of  the  bacteria  in  their  intestines.  Nevertheless,  it  is 
likely  that  there  are  many  more  bacteria  in  the  colon  than  can  be  said  to  be 
normal.  Those  which  are  the  most  offensive  decompose  the  proteids  and 
produce  thereby  a  large  number  of  substances  of  an  aromatic  and  almost 
alkaloidal  nature.  These  are  to  a  greater  or  less  extent  absorbed,  and 
probably  do  liarm,  in  ways  little  suspected  as  yet,  before  they  are  either 
decomposed  or  excreted  bodily  in  the  urine.  Coukl  the  proteid  food- 
fragments  in  the  colon  be  lessened,  much  of  this  baterial  growth  would 
be  checked.  These  fragments  probably  indicate  the  excessive  ingestion 
of  flesh-foods.  Work  by  Fletcher  and  by  Chittenden  has  shoAvn  a  prob- 
able excess  in  meat-consumption  by  all  but  tlie  j)oorest  classes  of  society. 


DIGESTION  213 

Could  the  amount  eaten  be  reduced  to  the  actual  needs  of  tissue-repair 
(and  in  case  of  chiUh-en,  of  tissue-growth),  decided  benefit  might  accrue 
to  that  large  class  of  persons  who  take  too  little  exercise  and  to  that  other 
large  class  whose  nervous  systems  have  become  too  imstable  for  normal 
"civilized"  living.  Persons  of  these  sorts  commonly  suffer  from  in- 
testinal atony,  and  the  resulting  too  complete  absorption  of  these  putre- 
factive products  may  be  the  still  unsuspected  source  of  much  disease. 


CHAPTER    VI. 

NUTRITION. 

Having  seen  how  the  food  is  digested,  we  next  naturally  inquire  as  to 
the  process  by  which  the  protoplasm  of  the  organism  is  supplied  with  its 
nutritive  material,  and  how  and  for  what  purposes  this  organized  fuel 
is  used  by  the  body. 

By  nutrition  we  mean  a  complex  of  vital  processes  in  part  included 
under  the  term  metabolism,  but  comprising  also  the  two  procedures^ 
absorption  and  excretion.  In  this  chapter  then  we  shall  take  up  the 
ultimate  food-materials  as  they  are  left  by  the  digestive  juices  of  the  gut 

Fig.  Ill 


The  summit  of  the  villus  in  the  gut  of  a  kitten,  showing  the  absorption  of  fat  by  the 
various  sorts  of  cells.      (Heidenhain.) 

and  leave  them  only  when  they  have  been  crudely  traced  through  their 
changes  in  the  body  and  excreted  outside  the  organism  again.  These 
processes  of  nutrition  in  part  form  a  link  of  this  physiological  chain — 
namely,  that  link  which  connects  the  digested  food  with  the  blood  and 
tissues  it  supplies.  So  far  as  metabolism  proper  is  concerned  there  are 
two  sorts  of  processes,  like  two  sides  of  an  isosceles  triangle  (see  Fig.  8), 
the  apex  of  which  between  them  is  the  normal  composition  of  the  blood 
and  tissues.  The  up-going  side  is  anal)olism,  constructive  assimilation; 
the  down-going  side  represents  the  katal)olism,  destructive  dissimilation. 
Introductory  to  these  two  (metabolism)  is  absorption,  while  as  a  neces- 
sary conscrjucnce  of  them  excretion  must  be  considered.  The  former 
process  introduces  the  nutriment   actually  into   the  blood  and  tissues; 


NUTRITION 


215 


while  excretion,  of  necessity,  removes  the  dead  waste  from  these,  lest  it 
poison  them.  Nutrition  then  is  more  than  metabolism,  and  constitutes 
a  definite  subject  of  fj;reat  importance  because  at  the  basis  of  every 
vital  process.  Our  discussions  of  protoplasm  and  of  food  are  intro- 
ductory to  the  descriptions  of  this  chapter,  yet  do  not  infringe  on  its 


Fio.  112 


Absorption 


fats. 


Excretion 


tmter. 
salts, 
detritus. 

External  nutrition.  Tlae  upper  picture  suggests  the  places  of  absorption  of  the  various  proxi- 
mate principles  into  the  villus.  The  lower  part  of  the  figure  indicates  diagrammatically  the 
various  excretory  organs  and  what  chiefly  passes  out  through  each. 

province   of   trying   to  explain  how  the  food  renews  the  ever-wasting 
body  and  supplies  it  with  energy. 

Nutrition,  like  respiration,  is,  for  descriptive  purposes,  of  two  sorts, 
external  and  internal.  External  nutrition  is  that  part  of  the  total  process 
by  which,  on  the  one  hand,  the  blood  receives  its  nutritious  elements,  and 
loses  its  excrementitious  portions,  on  the  other.  The  former  enter  it  from 
the  gut,  while  the  latter  leave  it  by  way  of  the  various  excretory  organs. 


216 


NUTRITION 


Internal  nutrition  is  the  portion  of  this  general  function  that  has  to  do 
with  the  passage  of  the  blood's  nutrients  into  the  tissues  and  of  the  tis- 
sues' waste  back  into  the  blood.  Both  parts  of  each  of  these  processes 
are  indispensable  to  life.  Of  external  nutrition  the  first  process  is  absorp- 
tion. 

Fig.  113 


The  periglandular  and  the  villous  plexuses  of  nerves  in  the  gut  of  the  porpoise:    a,c,f, 
triangular  and  stellate  cells;   b,d,e,  fusiform  cells.      (Ramon  y  Cajal.) 

Fig.  114 


~a 


Section  in  the  wall  of  the  small  gut  of  the  eel-pout.      The  arterien  are  shown  in  black,  the 
veins  cro.ss-striated,  and  the  lymphatics  granulated.      (Melnikow.) 


ABSORPTION. 

AKsorption  is  the  process  by   wliich  food  is  conveyed  directly  or  in- 
lirectly  into  the  circulating  blood  from  the  alimentary  canal.    From  the 


ABSORPTION 


217 


mouth  so  little  is  absorbed  that  it  may  be  disregarded  as  an  absorbing 
organ.    The  small  intestine  is  by  far  the  most  important  site  of  absorp- 


FiG.  115 


AB50RPT/0N. 
__^  heater  &  t5a//nes 
_^  Prote/cf^ 
. -^  C>3rbohydr<3tes 

—^  A/ke/ofds.  etc. 


This  diagram  suggests  in  general  the  places  where  the  various  nutrient  proximate  principles 
are  chiefly  absorbed  into  the  circulation. 

tion,  the  large  intestine  comes  next,  while  the  stomach  is  rated  last  in 
this  respect. 


218  NUTRITION 

Saline  and  otlier  aqueous  solutions  are  absorbed  bv  the  capillaries. 
The  principles  which  underlie  the  absorption  of  these  substances  are 
doubtless  those  of  the  obscure  physical  chemistry  of  filtration,  and 
especially  of  osmosis.  The  "selective  power"  of  the  epithelium  plays  an 
important  part,  but  this  selective  power  is  probably  only  a  matter  of  the 
complex  physical  aspects  of  chemism.  While  it  is  possible  that  the 
stomach  absorlis  some  of  the  salines  (as  it  does  alkaloids  and  alcoholic 
extracts),  both  the  small  and  large  intestines  are  the  chief  sites  of  the 
absorption  of  these  substances. 

Fat  is  distinguished  from  all  the  other  nutrient  principles  by  being 
absorbed  through  the  club-shaped  lymphatics  of  the  intestinal  villi,  and 
normally  by  no  other  route.  It  is  likely  that  the  lacteals  of  the  jejunum 
and  the  ileum  do  most  of  this  work.  Much  if  not  all  of  the  fat  absorbed 
is  first  split  into  fatty  acids  and  glycerin,  but  these  change  back  into 
neutral  fat  probably  before  lea\ang  the  epithelium  of  the  gut  on  their 
way  into  the  circulation.  It  is  likely  enough  that  the  leukocytes  of  the 
villi  have  something  to  do  with  the  transfer  of  fat-particles  inward. 
During  the  digestion  of  a  fatty  meal  the  lymph  of  the  great  ducts  may 
contain  15  or  20  per  cent,  of  fat  for  hours.  The  capillaries  also  take  up 
the  fat-globules  to  some  extent  when  the  amount  ingested  is  excessive. 
It  has  been  supposed  that  the  bile-salts  assist  in  the  absorption  of  the  fat, 
but  apparently  they  do  so  only  indirectly  through  their  emulsifying 
activities. 

Carbohydrates  are  absorbed  almost  wholly  as  dextrose  and  levulose 
by  the  capillaries  lining  the  intestines.  Probably  the  intestinal  epithelium 
changes  the  colloidal  dextrin,  cane-sugar,  milk-sugar,  and  even  starch  to 
dextrose  while  they  pass  through  it.  Reach  has  shown  that  sugar  is 
readily  absorbed  by  the  rectum,  and  this  is  a  matter  of  some  practical 
importance  in  therapeutics.  Everything  recently  discovered  goes  ta 
show  that  the  intestinal  epithelium  is  a  very  versatile  tissue,  acting  by 
means  of  the  potent  enzymes  as  well  as  by  those  selective  ("vital") 
pow'ers  afforded  by  its  chemical  and  perhaps  physical  composition. 

Protein  and  albuminoids  (which  may  be  discussed  together  so  far  as 
their  absorption  is  concerned)  also  appear  to  be  taken  up  wholly  by  the 
portal  capillaries.  In  what  exact  chemical  forms  these  complex  sub- 
stances enter  the  epithelium  and  in  w^hat  shapes  they  leave  it,  is  still 
under  active  discussion.  The  main  question  at  issue  discusses  how  far 
the  food-proteids  and  albuminoids  are  broken  down,  and  therefore  as  to 
the  exact  changes  produced  by  the  gut-epithelium  before  the  protei(  s 
and  albuminoids  reach  the  circulation.  The  question  cannot  be  exactly 
answered  as  yet.  It  is  the  capillaries  of  l)oth  the  large  and  small  intestines 
which  absorb  these  substances. 


METABOLISM. 

Metabolism  consists  of  both  the  u])-])nilding  process,  anabolism,  and 
the  dowii-t(  aring  process,  kataljolism.     These  terms  ai)j)ly  especially  to 


METABOLISM 


21^^ 


Fig.  116 


the  chemical  changes  in  the  hody-protoplasm  rather  than  to  food  in  tli  ,■ 
intestinal  wall. 

The  anabolic  processes  of  the  organism  are  as  yet  too  little  known  in 
their  details  to  warrant  even  an  attempt  to  describe  them  here.  The 
reason  for  this  lies  in  the  fact  that  the  chemistry  of  the  anal)olic  processes 
is  of  unique  complexity,  besides  being  everywhere  deeply  hidden  in  the 
protoplasm  of  the  intestinal  walls  or  of  the  tissue-cells. 

The  katabolic  processes  of  the  body,  in  which  the  tissue-protoplasm 
is  chemically  simplified  in  its  life-activities,  are  somewhat  more  acces- 
sible than  the  anabolic  processes,  and  in  consequence  they  have  been 
better  learned.  In  plants  the  opposite  is  true.  The  vital  processes  of  the 
vegetable  kingdom  are  essentially  anabolic,  while  the  phenomena  of 
animal  life  depend  on  chemical  reactions  of  a  katabolic  kind.  It  is  by 
kataliolism  that  an  animal's  body 
liberates  the  energy  by  which  it  lives. 
To  be  exact,  life  considered  biologi- 
cally is  metabolism,  especially  in  its 
katabolic  phase. 

Organic  Growth  and  Repair  in  its 
histological  aspects  is  not  a  subject 
germane  to  our  present  purpose,  but 
it  is  necessary  for  completeness'  sake 
to  look  briefly  at  the  processes  of 
anabolism  in  this  respect.  Until  the 
adult  stature  is  attained  the  body 
grows.  Gaps  made  by  wounds  are 
filled  in  l)y  new  tissues,  and  lost  blood, 
etc.,  are  gradually  regenerated.  It  is, 
of  course,  a  prime  characteristic  of 
living  matter  to  be,  from  use  or  de- 
generation, continually  wasting,  and 
this  loss  must  be  as  continually  re- 
placed. These  and  the  other  wastes  of  animal  tissue  the  food  and  the 
respiratory  oxygen  restore.  As  we  have  seen  already  in  Chapter  IV,  only 
the  proteids  of  food  are  capable  of  supplying  adequately  both  tissue  and 
energy  to  the  animal  organism,  the  other  "proximate  principles"  having 
only  special  values  in  this  direction.  How  then  are  the  proteid  anabolic 
processes  conducted  to  this  primary  organic  end  of  growth  and  repair? 

Pfliiger's  In-pothesis  has  much  interest:  "In  the  making  of  cell-sub- 
stance, i.  e.,  of  living  proteid,  out  of  the  proteid  of  the  food  a  change 
occurs  in  the  latter,  the  nitrogen-atoms  going  into  a  relation  with  the 
carbon-atoms  like  that  in  cyanogen,  with  probably  the  absorption  of 
much  heat."  This  introduction  of  the  cyanogen-radical  into  the  vital 
molecule  of  the  tissues  introduces  into  it  lively  energy  as  motion,  heat, 
etc.,  but  also  something  which  is  of  more  immediate  interest  here — the 
power  of  spontaneously  growing  and  of  wasting.  In  a  word,  proteid 
anabolism  means  the  power  of  spontaneous  metabolism,  of  interchanging 


Fat  cells  from  the  subcutaneous  connec- 
tive tissue  of  an  embryo  calf  of  45  cm. 
in  length.  In  a  the  fat  globules  are  few 
and  small;  in  b  some  have  coalesced;  in  c 
still  more;  while  in  d  nearly  the  whole 
mass  of  the  cell  is  fat.      (Ranvier.) 


220  NUTRITION 

atoms  or  ions  or  lesser  molecules  (whichever  it  may  be)  within  itself  so 
that  growth  is  possible.  Conjectures  as  to  the  exact  mode  of  this  proteid- 
growth  are  well-nigh  vain,  so  little  do  we  know  of  the  structure  of  the 
biomolecule  or  vital  group,  while  of  the  proteid  molecule  itself  we  know 
but  little  more.  One  conjecture,  however,  seems  reasonable — namely, 
that  this  protoplasmic  unit  or  group  (whatever  in  exact  physical  terms 
it  may  prove  to  be)  increases  in  complexity  by  development  and  accretion 
up  to  a  certain  limit  and  then  breaks  up  into  daughter-units  (each  based 
on  a  cyanogen-root),  which  thereupon  grow  and  split  in  turn.  The 
developments  which  occur  in  this  (protoplasmic)  tissue-unit  take  place 
probably  all  through  it  and  not  on  its  periphery  only.  In  other  words, 
growth  is  real,  inherent  development  and  not  mere  accretion  from  without, 
for  else  the  complexities  of  metabolism  could  not  be  accounted  for 
(Hering).  By  some  method  the  food  that  serves  as  the  means  of  ana- 
bolism  supplies  particles  of  just  the  required  composition,  etc.,  to  the 
tissue-units,  and  these  thereupon  grow  and  split  up  and  so  form  a  new 
particle  of  protoplasm.  Finally,  unknown  multitudes  of  these  biogenic 
particles  become  a  tissue-cell,  the  morphological  unit,  with  its  organiza- 
tion of  nucleoplasm  and  cytoplasm,  familiar  in  every  perfect  cell. 

It  cannot  be  doubted  that  water,  inorganic  salts,  fats,  and  carbohy- 
drates take  part  simultaneously  with  proteid  in  the  anabolic  tissue- 
growth.  It  seems  probable,  however,  that  the  fats  and  carbohydrates 
are  not  so  intimately  concerned  in  the  formation  of  new  protoplasmic 
units  as  are  the  proteid,  the  inorganic  salts,  and  water.  The  proteid 
doubtless  forms  the  core  or  basis  of  the  unit,  and  either  contains  or 
carries  the  salts.  The  water  is  always  inherent  and  basal  in  protoplasm. 
The  fats  and  carbohydrates  are  perhaps  related  to  this  cyanogenic  unit 
as  necessary  foodstuffs  to  lend  it  strength,  thereby  making  its  manifold 
metabolism  and  activity  possible.  Each  sort  of  tissue-unit  has  the 
power  of  taking  on  from  the  lymph  precisely  those  molecules  of  food 
which  it  needs,  and  each  has  the  means  of  preventing  the  attachment 
of  those  it  does  not  require.  In  this  way  it  is  self-perpetuating.  At 
the  same  time,  still  more  marvellously  perhaps,  every  vital  unit  has 
the  faculty  of  developing  to  meet  those  entirely  novel  requirements 
which  new  habits,  new  uses,  and  new  environments  are  continually 
making  essential  in  animal  life.  How  else  can  we  account  for  the 
molec-ular  development  of  a  scholar's  brain,  the  cunning  of  the  muscles 
of  a  human  hand,  or  the  adaptation  to  new  needs  of  the  organ  of  Corti 
in  a  musician's  ear? 

The  remainder  of  this  chapter  deals  with  manifestations  of  metabolism 
more  largely  in  its  katabolic  phase. 

Secretion. — Between  the  process  we  have  considered  as  growth  and 
the  father  only  less  general  phenomenon  we  shall  now  describe  as 
secretion  the  differences  are  mainly  arbitrary,  but  obviously  with  this 
exception:  While  in  tissue-growth  the  new-formed  substance  becomes 
and  remains  for  a  time  a  part  of  the  mother-tissue,  in  secretion  the 
jjroduct  must  of  necessity  1k'  removed  with  more  or  less  promptness.     In 


METABOLISM  221 

secretion,  moreover,  the  product  of  the  cell-metaboHsm  is  more  unHke 
the  secreting  protoplasm  than  in  the  case  of  growth.  The  former  process 
is  more  Hke  manufacture,  while  the  latter  more  resembles  reproduction. 
A  difference  that  is  only  apparent  is  that  the  product  in  growth  is  "solid" 
and  in  secretion  usually  liquid.  Witness,  however,  the  liquidity  of  the 
tissues  generally  and  the  solidity  of  the  grains  of  glycogen  in  the  liver- 
cells.  So  far  as  the  metabolic  changes  occurring  in  the  living  unit  are 
concerned,  we  can  state  no  important  differences  between  growth  and 
secretion  save  that  the  former  is  largely  aiiabolism  anrl  the  latter  mostly 
katabolism.  As  secretion  is  the  chief  function  of  all  the  epithelial  and 
lymphoid  tissue  of  the  organism,  it  has  an  organ  of  its  own,  but  growth 
is  common  to  all  the  tissues. 

Broadly  speaking,  however,  secretion  too  is  a  function  of  all  protoplasm, 
inasmuch  as  the  process  involves  only  the  production  of  some  material 
substance  by  an  organic  tissue.  Thus,  one  sees  amebse  (the  individuals  of 
which  consist  each  of  "only  a  drop  of  protoplasm")  surrounding  proteid 
food-particles,  absorbing  them  intimately  into  the  homogeneous  colloidal 
matter  of  that  part  of  the  body  that  is  by  chance  concerned,  and  then 
soon  enclosing  them  by  a  food-vacuole  filled  with  digestive  juices  secreted 
apparently  from  that  part  of  the  protoplasm  that  happens  to  be  imme- 
diately about  it. 

It  must  not  be  imagined  that  even  in  man  the  tissues  in  general  have 
lost  their  power  of  secretion.  It  appears,  on  the  contrary,  that  every 
tissue  produces  certain  particular  enzymes  that  in  part  control  its  own 
special  sort  of  metabolism.  The  substances  needed  widely  or  in  large 
amounts  or  in  certain  organs  are  produced  in  special  epithelia,  but  every 
true  cell  of  the  body  seems  to  be  the  secretor  of  its  own  metabolic  deter- 
minants, as  ameba  obviously  is.  The  details  of  this  matter,  all  new 
since  knowledge  of  the  internal  secretions  began  to  accumulate,  are 
still  unknown,  and  will  largely  remain  so  until  at  least  the  chemical 
nature  of  protoplasm  is  better  learned.  In  this  broad  meaning  of  the 
term  secretion  there  is  included  both  absorption  and  excretion,  and 
metabolism  is  evidently  nearly  its  s}nonym. 

Underlying  all  the  secretory  and  absorptive  functions  of  the  body  is 
the  process  which  is  known  to  physics  as  osmosis.  The  nature  of  tliis 
series  of  events  must  be  somewhat  understood  as  a  basis  for  compre- 
hending what  goes  on  in  the  protoplasm  of  the  general  tissues. 

Osmosis  (from  the  Greek  "pushing")  is  the  passing  or  mixing  of 
liquids  through  membranes  immersed  in  them.  Abbe  Nollet  first 
noticed  the  phenomenon  in  1748.  He  observed  that  a  bladder  full 
of  alcohol  immersed  in  water  soon  became  overdistended  with  the  water 
that  passed  into  it,  the  water  pushing  inward  through  the  membrane 
faster  than  the  alcohol  moved  outward.  It  has  much  more  recently 
been  shown  by  Pfeffer,  working  with  plant-cells,  that  the  pressure 
exerted  by  any  solution  whose  molecules  do  not  dissociate  into  ions 
is  equal  to  the  gaseous  pressure  which  would  be  created  by  a  like  mass 
of  the  dissolved  substance  vaporized  and  confined  in  a  space  equal  to 


222 


NUTRITION 


that  of  the  sohition.  As  to  how  the  dissolved  salt  exerts  its  pressure 
nothing  is  really  known,  although  there  are  theories  a-plenty.  One 
observer  supposes  that  the  dissolved  salt  exists  in  the  interstices  between 
the  molecules  of  the  solvent  in  the  state  corresponding  to  a  perfect  gas, 
and  hence  that  the  stronger  the  solution  the  greater  its  pressure  through 
a  membrane  toward  a  weaker  solution.  Another  view  (Poj^iting's)  is  that 
"the  phenomenon  known  as  osmotic  pressure  arises  from  the  molecules 
of  salt  clinging  to  the  molecules  of  water,  and  so  diminishing  the  mo- 
bility and  therefore  the  rate  of  diffusion  of  the  latter,"  each  molecule  of 
salt  completely  impeding  the  movement  of  one  molecule  of  water. 

Ions,  the  parts  into  which  the  molecules  of  many  crystalloids  dissociate, 
act  as  regards  the  production  of  osmotic  pressure  just  as  would  whole 
molecules.     It  is  supposedly  on  this  account  that  a  solution  of  an  inor- 


FiG.  117 


Diagram  to  show  osmosis  through  the  vital  membranes  (cells  of  the  spiderwort,  Tradescantia) : 
A.  When  the  cell  is  put  in  a  dissociated  solution  (electrolyte)  having  the  same  pressure  as  that 
of  the  electrolytes  of  the  cell  biogen,  no  changes  are  apparent,  and  if  in  a  less  pressure  solution 
the  cellulose  wall  prevents  the  expansion  which  else  would  be  obvious  (more  water  passing  in 
than  electrolyte  out).  B  and  C.  If  immersed  in  a  solution  of  stronger  osmotic  pressure,  the 
opposite  movement  occurs  and  the  biogen  is  retracted.      (Jones.) 

ganic  acid  or  salt  exerts  more  osmotic  pressure  than  does  an  isotonic 
(equally  pressing)  solution  of  organic  acids  or  salts,  for  many  of  the  latter 
do  not  dissociate  into  ions.  The  solutions,  then,  whose  molecules  disso- 
ciate-most will  exert  the  greatest  osmotic  pressure.  Moreover,  as 
Arrhenius  showed,  when,  for  example,  sodium  chloride  dissolves  in  water, 
some  of  its  molecules  dissociate  into  sodium  ions  and  chlorine  ions. 
'J'he  former  are  then  bearers  of  positive  "electrons"  and  the  latter  of 
negative  "electrons."  By  means  of  these  electrons  the  solution  conducts 
electricity,  and  is  called,  therefore,  an  electrolyte.  The  greater  the 
conductivity  of  an  electrolyte  the  greater  is  its  osmotic  pressure.  A 
.solution  of  sodium  chloride,  therefore,  injected  into  a  mass  of  protoplasm 
that  flissofiatcs  little  tends  to  leave  it,  owing  to  its  greater  osmotic 
pressure,  until  a  balance  is  found.  It  is  on  this  principle,  in  part,  that 
the  tissues  maintain  their  accustomed  normal  composition  and  perform 
some  of  their  secretorv  funrtions. 


METABOLISM  223 

The  reciprocal  relation  between  dissociation,  osmotic  pressure,  and 
the  freezing-point  of  a  solution  presents  a  ready  way  of  finding  the 
osmotic  pressure  of  any  solution  without  testing  it  directly,  and  to  deter- 
mine its  freezing-point  is  much  simpler.  The  greater  the  dissociation, 
and  so  the  more  molecules  a  solution  contains,  the  greater  is  its  pressure 
and  the  lower  its  freezing-point.  A  gram-molecular  solution  is  one  con- 
taining as  many  grams  dissolved  as  there  are  units  in  its  molecular  weight. 
Such  a  solution  wherein  no  dissociation  occurs  has  been  found  to 
lower  the  freezing-point  l.S6°  C.  If,  then,  we  find  by  means  of  an 
apparatus  for  the  purpose  how  much  lower  than  that  of  pure  water  is 
the  freezing-point  of  the  solution  whose  osmotic  pressure  is  desired, 
we  need  only  to  divide  the  fraction  of  a  degree  of  the  lowering  (expressed 
A)  by  the  constant  1.86  to  have  the  desired  percentage  of  the  lowering 
of  the  osmotic  pressure.  A  gram-molecular  solution  of  a  non-electrolyte 
(no  dissociation)  exerts  a  pressure  of  22+  atmospheres,  and  the  per- 
centage of  lowering  of  the  pressure  found  multiplied  by  this  number  gives 
the  osmotic  pressure  desired  in  atmospheres.  The  pressure  is  propor- 
tionate to  the  concentration,  a  2  per  cent,  solution  of  an  electrolyte 
pressing  twice  as  much  as  a  1  per  cent,  solution  of  the  same  substance. 

By  the  freezing-point  method  we  may,  then,  determine  not  only  the 
osmotic  pressure  of  any  solution,  whether  an  electrolyte  or  not,  but  also 
the  degree  of  its  electrolytic  dissociation  in  case  the  solution  be  an  electro- 
lyte. This  latter  datum  seems  often  to  be  of  essential  importance  as 
regards  the  effects  of  saline  electrolytes  on  protoplasm. 

One  of  the  most  surprising  things  to  the  student  of  these  matters  at 
first  is  the  great  pressures  exerted  by  solutions  of  this  sort.  Osmosis  is 
clearly  one  of  the  great  forces  of  organic  nature,  and  it  acts  ever}^here 
in  plants  and  animals,  and  yet  so  quietly  as  to  remain  unsuspected  save 
in  its  effects  until  the  refinements  of  modem  physical  chemistry  made  it 
manifest. 

"Vitalism." — This  term  is  sometimes  useful  in  biological  discussions, 
but  its  meaning  nowadays  is  much  less  significant  than  it  was  fifty  years 
ago  when  the  principles  of  physics  and  of  chemistry  had  not  as  yet  been 
applied  to  living  processes.  Indeed,  the  term  vitalism  then  implied 
distinctly  that  organic  reactions  (absorption,  secretion,  etc.)  were  char- 
acteristic and  unique,  and  essentially  different  in  kind  from  those  outside 
of  living  protoplasm.  Today  we  know  or  at  least  think  we  know  in 
what  ways  the  vital  processes  are  characteristic  and  different — namely, 
in  their  subtlety,  complexity,  and  intricacy  of  interaction,  and  so  far  as 
we  know  only  in  these  ways.  Vitalism,  then,  today  means  only  the  sum 
total  of  the  chemiphysical  reactions  of  vital  matter.  AMiether  these  will 
be  known  in  detail  sometime  cannot  be  foretold.  The  important  thing 
is  that  their  nature  is  such  that  they  might  be  known  in  detail  were  our 
methods  refined  enough,  when  without  a  doubt  they  would  be  found  to  be 
in  kind  like  the  rest  of  Nature. 

The  phenomena  of  secretion  are  the  secretory  events  so  far  as 
study  of  secreting  and  absorbing  epithelia  reveals  them  to  us  through 


224 


NUTRITION 


the  microscope  or  by  chemical  analysis.  Obviously  the  active  produc- 
tion of  a  new  substance  by  the  protoplasm  of  a  secreting  cell  necessitates 
some  degree  of  loss  in  that  protoplasm,  for  the  time  being  at  least.  On 
the  basis  of  the  degree  of  this  destruction  of  the  epithelial  substance  we 
may  distinguish  three  types  of  secretion  proper:  In  the  first,  the  most 
common,  the  protoplasm  is  not  obviously  lessened,  the  preliminary 
product  (zymogen)  appearing  as  granules,  etc.,  within  the  cell-body. 
In  the  second  type  the  upper  part  of  the  cell-body  becomes  in  a  mass  the 


Fig.  118 


MJB. 


^M.B, 


Diagram  of  a  gland:  M.B.,  basement-membrane;  £,  epithelium;  D,  gland-duet;  N.C.,  nerve- 
center;  M ,  mental  influence;  <S,  "sensory"  influence  from  the  basement-membrane;  N,  direct 
influence  on  the  cell-protoplasm ;  y..V.,  vaso-motor  influence;  .1,  artei-y;  F,  vein.    (Lecture-chart.) 


secretory  prochut;  of  this,  milk-secretion  is  the  best  example.  In  the 
third  sort  of  secretion  the  whole  cell-body  passes  off  as  the  product; 
mucous  secretion  is  the  type  of  this,  and  sebum  the  other  chief  instance. 
As  hinted  above,  many  sulrstances  are  given  out  by  epithelium  that  do 
not  appear  to  view  at  all.  These  pass  out  of  the  protoplasm  by  osmosis 
or  diffusion,  and  are  crystalloids,  gases,  or,  rarely  perhaps  liquids. 
About  these  invisible  secretory  phenomena,  purely  metabolic  in  nature, 
little  is  known  as  yet.     The  secretion-products  with  which  we  are  now 


METABOLISM 


225 


concerned,  then,  are  for  the  most  part  colloids,  which  do  not  readily 
osmose.  They  therefore  do  not  make  their  way  out  of  the  cell  as  fast  as 
formed,  like  the  others,  but  collect  in  the  cytoplasm,  and  either  osmose 
out  of  it  slowly  or  pass  off  bodily  in  a  mass.  Among  these  substances 
are  proteids,  fats,  glycogen,  mucin,  and  numerous  other  products  of 
anabolism,  even  less  known  than  these,  such  as  enzymes,  pigments,  and 
* 'extractives"  of  many  sorts  and  uses.  Many  of  these  products  probably 
have  molecules  so  large  and  unstable  (because  complicated  and  loosely 
composed  within)  that  they  are  broken  up  into  parts  before  passing  out 
of  the  cell.  This  is  the  case  particularly  with  the  granules  which  are 
conspicuous  in  secretory  processes  of  the  first  type  {e.  g.,  in  salivary, 
pancreatic,  hepatic  cells).  In  case  of  mucus,  not  diffusible  through 
membranes,  the  cell  gives  way  bodily  and  allows  the  product  to  escape 
freely  into  the  lumen  of  the  gland. 


Fig.  119 


C  D 

Secreting  epithelium  (parotid  of  a  rabbit),  to  show  the  process,  so  far  as  to  be  seen  under  the 
microscope:  .4.,  resting,  B,  after  action  occasioned  by  pilocarpine;  C,  after  more  vigorous  action 
occasioned  by  both  pilocarpine  and  stimulation  of  the  sympathetic;  D,  after  long-continued 
action  from  stimulation  of  the  sympathetic.      (Langley.) 

The  internal  secretions  are  poured  into  the  blood  instead  of  into 
the  gut  or  on  the  skin.  Among  those  of  chief  importance  so  far  dis- 
covered are  those  produced  by  the  pancreas,  the  duodenum,  the  liver,  the 
thyroid,  the  thymus,  the  pituitary  body,  the  adrenals,  the  kidneys,  the 
spleen,  the  testes,  and  the  ovaries.  In  addition  to  these,  the  coccygeals 
and  the  carotids  produce  internal  secretions  of  unknown  value,  while 
all  the  lymphoid  tissues  secrete  lymph.  We  can  here  mention  only  in  a 
most  summary  way  the  uses  of  these  various  products  secreted  into  the 
circulation.  Little  is  as  yet  learned  about  them  probably  compared 
with  what  some  day  will  be  known. 
15 


226 


NUTRITION 


It  Is  generally  supposed  that  the  internal  secretion  of  the  "islands  of 
Langerhans"  of  the  pancreas  has  control  over  the  oxidation  or  other 
destructive  metabolism  of  the  dextrose  of  the  blood  and  tissues.  Schiiltze 
finds  evidence  in  addition  that  this  product,  like  that  of  the  pituitary 
body,  regulates  the  blood-pressure  of  the  vessels.  The  internal  secre- 
tions of  the  duodenum  have  been  already  discussed  in  the  chapter  on 
Digestion.  iVmong  these  are  secretin  and  kinase  (entero-kinase). 
Some  claim  that  secretin  is  the  product  of  all  the  tissues  in  the  body  as 


Fig.  120 


Tubular  filands. 


Alveolar  glands. 


.  w 


A  diaKram  of  various  typical  forms  .of  gland.'*:    a,  duct;   x,  simple  tubule;   xx,  simple 
alveolus.      (Szymonowicz  and  MacCallum.) 


well  as  of  the  duodenal  wall.  The  internal  secretions  of  the  liver  are 
glycogen  and  an  enzyme,  sometimes  called  urease,  which  has  the  power 
of  f(irmiiig  urea  from  some  of  the  decomjjosition-products  of  proteid. 
Schiifer  suggests  that  perhaps  by  means  of  an  internal  secretion  the  liver 
saves  the  iron  from  the  breaking  down  red  blood-corpuscles  which 
otherwise  would  be  lost  to  the  body.  The  thyroid,  either  by  means  of  a 
peculiar  substance  called  colloid  which  collects  in  the  alveoli  (and 
absorljed   by  the  lymph),  or  by  less  obvious  products  which  pass 


IS 


METABOLISM 


227 


it  directly  into  the  blood,  or  by  both  of  these,  exerts  some  essential 
influence  over  the  processes  of  metabolism.  Removal  of  the  organ 
early  in  life  creates  the  condition  of  peculiar  idiocy  known  as  cretinism. 
Extensive  disease  of  this  organ  in  adult  years  gives  rise  to  a  set  of 
similar  symptoms  called  myxedema.  The  symptoms  of  this  disease 
may  apparently  be  attributed  to  the  disturbance  in  the  nutrition  of  the 
nervous  system  and  of  the  connective  tissue.     Kirshi's  work  indicated 


Fig.  121 


The  circulation  of  iron.  It  is  possible  at  least  that  by  some  such  route  as  this  the  iron  liber- 
ated continually  from  the  weanng-out  erythrocytes  is  saved  to  the  organism  for  re-use.  Ingested 
in  the  food,  it  passes  into  the  hone-marrow,  is  used  as  part  of  the  hemoglobin  in  the  circulation, 
is  saved  by  the  spleen,  made  into  bile-pigments  in  the  liver,  absorbed  by  the  colon,  and  then 
made  over  into  hemoglobm. 

that  the  para-thyroids  are  embryonal  tissue  present  in  the  body  to 
serve  as  substitutes  in  case  the  thyroids  are  diseased.  Injection  of  the 
extract  of  the  thyroids  of  animals  or  even  the  successful  implantation 
of  their  living  thyroids  into  the  abdominal  cavity  often  cures  these  condi- 
tions of  cretinism  and  myxedema. 

The  internal  secretion  of  the  thymus,  which  is  especially  prominent  in 
the  fetus  and  in  childhootl.  appears  to  have  something  to  do  with  fitting 


228 


NUTRITION 


Fig.  122 


out  the  leukocytes  for  their  numerous  functions.  It  has  been  suggested 
that  this  organ  in  the  fetus  is  the  mother-tissue  of  all  the  lymphoid  tissue 
of  the  adult.  The  'pituitary,  sometimes  called  the  hypophysis  cerebri, 
is  a  vascular  mass  situated  at  the  base  of  the  brain,  and  weighs  only 
one-half  gram.  According  to  Schafer  and  Vincent,  extract  of  the  pitui- 
tary body  causes  a  rise  or  fall  in  the  blood  pressure,  an  effect  which  is 
probably  brought  about  through  the  vagus.  Its  removal  by  disease 
or  mechanically  causes  sometimes  death  and  sometimes  the  symptoms 

of  acromegaly,  a  condition  character- 
ized by  the  aberrant  overgrowth  of 
the  bones  of  the  face,  skin,  and  ex- 
tremities. The  extract  of  the  pitui- 
tary body  is  said  to  be  thirty  times 
stronger  than  that  of  the  adrenals. 
The  adrenals,  formerly  called  the 
supra-renal  capsules,  secrete  into  the 
circulation  a  substance  which  when  in- 
jected into  a  vein  causes  a  powerful 
vaso-constriction  in  the  arterioles  and 
corresponding  changes  in  the  heart 
itself.  Less  than  eight  hundred-thou- 
sandths of  a  gram  (0.00008  gm.)  of 
adrenalin  chloride  are  sufficient  to 
affect  the  blood-vessels  and  heart  of 
a  man  for  a  short  time.  Vincent  has 
shown  that  the  adrenals  contain  two 
sorts  of  glands,  those  of  the  rind  and 
those  of  the  interior.  Of  the  function 
of  the  former  nothing  is  known.  The 
others  are  apparently  concerned  in 
maintaining  the  tone  of  the  muscu- 
lature, perhaps  by  controlling  the  oxi- 
dation of  the  tissues.  The  kidneys 
appear  to  have  as  their  contribution 
to  the  agents  of  tissue-metabolism  a 
proteolytic  enzyme  which  when  carried 
to  the  liver  and  perhaps  to  all  the  tissues 
of  the  body  leads  to  the  production  of  urea.  The  internal  secretion  of  the 
spleen  has  been  assigned  many  functions.  All  of  these  are  complicated, 
but  none  of  them  are  at  all  established,  and  we  need  not  even  mention 
them  at  this  time.  The  testes  and  the  ovaries  apparently  have  substances 
secreted  by  their  epithelium  which  have  a  tonic  influence  over  the  nervous 
system,  especially  in  relation  with  the  muscles.  Injections  of  the  extracts 
of  these  two  organs  increases  nervous  vigor  and  muscular  tone,  and 
semen  exerts  somewhat  similar  effects. 

Animal  Heat.--'i'he  third  of  the  manifestations  of  the  general  metab- 
olism which  we  shall  specify  is  animal-  or  body-heat.     It  is  a  process 


The  thyroid  and  the  inner  thymus  of  a 
newborn  child:  1,  larynx;  2,  trachea; 
3,  medial  lobe;  4,  lateral  lobe;  5,  apex  of 
the  thyroid;  6,  medial  lobe;  7,  lateral  lobe 
of  the  thymus.      Natural  size.     (Rauber.) 


METABOLISM 


229 


so  largely  derived  from  katabolic   changes  that  we  place  it  in  that 
category. 

In  respect  to  their  maintenance  of  bodily  warmth,  animals  are  divided 
into  two  classes,  homotherms  and  poikilotherms,  these  terms  corre- 
sponding to  the  older  designations  "warm-blooded"  and  "cold-blooded" 
animals,  respectively.  These  phrases  are  scientifically  misleading,  for 
a  so-called  cold-blooded  animal  may  in  summer,  even  in  the  temperate 
zone,  have  a  higher  temperature  than  a  "warm-blooded"  animal  in  the 
same  place.  The  terms  homothermal  and  poikilothermal,  on  the  contrary, 
well  represent  the  physiological  conditions.  The  former  in  the  Greek 
means  "of  the  same  temperature,"  and  indicates  that  such  animals — 
namely,  birds  and  mammals — maintain  their  heat  at  a  relatively  constant 
degree  despite  changing  conditions,  sometimes  internal  as  well  as  external, 
The  term  poikilothermal  means  "of  a  varied  temperature,"  thus  implying 

Fig.  123 


1 

1 

I        i    1    i 

\      \   \          1 

Vt' 

1 

'    1    ' 

i       i   i 

30° 
26? 

^ 

1        ! 

1    ! 

1      ill      U- 

>. 

1    1    i 

i    1 

1  j-'^^r' 

i\ 

'    i    '.. 

Lij,-,-^'?''^ 

i        I        1 

M  ;  i 

_2-^^^!    !    i    '  J 

i        1 

»nJ   y^ 

"!  1 

J^.-^-^ 

\. 

1 

f  1 

'-. 

(•-i-t. 

L"o^ 

/ 

V 

"— 

«,, 

J 

/ 

•«..  , 

/ 

f 

• 

1 

C 

)•> 

1 

h 

? 

h 

a>» 

The  variation  of  a  poikilotherm  temperature  with  that  of  its  environment  (tortoise). 
With  an  initial  temperature  of  13°,  placed  in  a  temperature  of  37°,  in  three  hours  there  was  a 
rise  to  nearly  33°.  With  an  initial  temperature  of  33.5°,  placed  suddenly  in  en^^ronment  at  10°, 
its  temperature  in  three  hours  had  fallen  to  about  17.5°  (broken-line  cur\-e).      (Richet.) 


that  the  temperature  of  such  animals  is  not  constant  but  variable  (with 
the  environment).  As  is  usually  the  case  in  Nature,  the  dividing  line 
between  the  two  classes  is  not  absolute,  for  several  animals  on  the  lower 
margin  of  mammalia,  so  to  say,  are  only  imperfect  homotherms,  while  a 
number  of  other  mammals  become  poikilotherms  during  their  periods 
of  hibernation.  On  the  other  hand,  one  or  two  of  the  reptiles,  e.  g., 
the  python,  maintains  its  temperature  10°  or  15°  above  that  of  the  sur- 
rounding air,  showing  a  tendency  to  homothermy.  In  general,  however, 
the  division  practically  holds  that  all  animals  save  birds  and  mammals 
are  poikilothermous.  The  difference  of  these  two  sorts  of  animals  is 
sufficiently  striking.  Frogs,  for  example,  are  sometimes  received  in  the 
laboratories  in  winter  with  their  abdominal  fluids  obviously  frozen, 
yet  placed  in  tepid  water  for  a  few  minutes  the  animals  are  as  lively  as 
ever.     Six  months  later  one  of  the  same  frogs  might  have  a  temperature 


230 


NUTRITION 


•warmer  by  35°  C.  Contrast  with  this  the  conditions  in  mammals.  Many 
healthy  persons,  for  example,  go  through  life  with  a  temperature-varia- 
tion of  less  than  2°  C,  while  we  may  be  sure  that  the  heat-range  of  the 
average  individual  is  not  over  4°,  say  from  36°  to  40°  C.  (96.8°  to 
104°  F.).  (Unless  otherwise  stated,  all  temperatures  in  this  book  are 
in  the  Celsius  (centigrade)  scale.)  Parry  and  Lyon  observed  that  the 
temperature  of  an  Arctic  fox  in  a  temperature  of  —3.5.6°  was  38.3°,  while 
Davy  found  the  temperature  of  a  trout  in  water  at  4.4°  to  be  5.6°. 
Thus  the  temperature-range  of  the  "cold-blooded"  animal  averages 
nearly  ten  times  that  of  the  warm-blooded  bird  or  mammal.  The  reasons 
for  this  difference  are  mainly  two:  poikilotherms  have  a  much  less 
active  metabolism  than  have  homotherms,  and  they  have  no  elaborate 
mechanism  for  maintaining  a  constant  temperature  such  as  is  found  in 
birds  and  mammals.  Both  this  katabolism  and  this  mechanism  will 
be  found  described  in  their  proper  places. 

Fig.  124 


30:9 

30-8 


30:5 


JllnuW  I      II    III  IV     V     VI   VIIVIIIIX    X    XI  Midi    I      II    III   IV     V     VI  VII VHI  IX    X    XIMinutel     n 

Hourly  variation  in  the  internal  human  temperature  as  given  by  Forel.  On  the  left  are  the 
degrees  of  the  Celsius  scale,  and  at  the  bottom  the  hours  of  the  day,  beginning  at  midnight. 
The  extreme  variation  is  nearly  0.8°  C. 

Human  Temperature  is  of  much  clinical  importance,  because  it  indicates 
better  than  any  other  one  thing  many  conditions  of  illness  and  their 
progress,  and  no  other  artificial  instrument  is  so  indispensable  to  the 
physician  as  his  clinical  thermometer.  As  is  the  case  with  all  biological 
data,  average  temperature  or  mean  temperature  is  more  or  less  misleading, 
for  each  patient  is  a  unique  individual,  varying  more  or  less  from  every 
average;  none  the  less,  averages  and  means  have  u.se.  It  is  customary, 
therefore,  to  .speak  of  the  normal  human  temperature  as  about  37.1° 
(98.8°  F.  nearly).  This  is  a  few  tenths  of  a  (legree  too  high  for  men 
and  a  few  tenths  too  low  for  women,  especially  for  female  children. 
In  the  axilla,  too,  it  is  slightly  less  than  this,  and  in  the  rectum  or  vagina 
or  stream  of  urine  nearly  1°  more.  Other  normal  cau.ses  of  variation 
act  on  the  principle  that  the  more  inten.se  the  body's  metabolism  the  higher 
is  the  degree  of  heat  produced.  Thus,  the  temperature  is  somewhat 
higher  after  meals,  in  the  day  than  in  the  night,  at  sun.s(>t  than  at  sunrise^ 


METABOLISM 


231 


during  muscular  or  mental  or  glandular  work,  in  very  young  persons,  and 
in  small  individuals,  these  conditions  being  examples  of  especially  active 
katabolism.  The  normal  diurnal  variation,  say  between  5  a.m.  and  5  p.m., 
is  nearly  1°,  in  yoinig  children  and  nervous  women  often  more — a  fact 
often  forgotten  by  physicians.  The  extreme  range  compatible  with  life 
is  large.  Reincke  reported  a  rectal  temperature  of  24°  in  a  drunkard 
exposefl  to  cold  and  water,  and  he  survived.  ^lost  of  the  persons  who 
"freeze  to  death"  are  victims  of  alcohol  rather  than  of  cold.  Teale 
saw  an  hysterical  woman  with  a  temperature  of  50",  and  Donkin  recorded 
44.2°,  44.5°,  and  45°,  recovery  taking  place;  Richet  collected  degrees  of 
heat,  not  fatal,  even  as  high  as  46°.  But  a  temperature  of  41.5°  (106.7° 
F.)  or  even  41°  continued  for  several  hours  in  an  adult  is  very  dangerous. 
Halliburton  has  recently  isolated  from  neural  tissue  a  cell-globulin 
which  coagulates  at  from  45°  to  50°C.  This  is  especially  abundant  in 
the  nervous  gray-matter,  but  probably  occurs  in  most,  if  not  in  all,  cells. 

Fig.  125 


Diagram  of  the  relative  temperatures  of  the  blood  in  various  parts  of  the  human  body.    The 
liver's  temperature  is  highest  and  that  of  the  systemic  veiniets  the  lowest.     (Langlois.) 


A  temperature  of  47°  leads  to  an  instantaneous  disappearance  of  the 
chromatophile  granules  of  the  nerve-cells,  but  44°  also  brings  this  about 
after  two  hours.  He  supposes  that  the  coagulation  of  this  globulin, 
therefore,  is  the  cause  of  death  when  the  body-temperature  stays  at  this 
point  or  passes  much  beyond  it,  that  is,  about  110°  F.  Insolation 
(sun-stroke),  scarlet  fever,  influenza,  and  meningitis  are  perhaps  the 
commonest  causes  of  very  high  temperatures. 

Depression  of  the  degree  of  heat  below  the  mean  is  comparatively 
infrequent.  To  the  extent  of  0.5°  or  so,  however,  it  is  not  uncom- 
mon, the  most  frequent  causes  being  alcohol  and  exposure  to  cold 
water.  The  temperature  of  animals  other  than  man  we  need  not 
consider  here.  In  general  those  of  poikilotherms  are  1°  or  2°  above 
their  environments,  while  those  of  homotherms  range  near  that  of 
man,  usually  within  1°  or  2°,  those  of  birds  being  especially  high.  The 
phenomena  of  hibernation  will  be  considered  later. 


232 


NUTRITION 


Thermotaxis. — The  heat  and  other  energy  of  the  animal  body  are  pro- 
duced verv  largely  by  two  sorts  of  processes.  One  of  these  is  chemical — 
namely,  metabolism  (chemism),  the  other  mechanical,  friction.  Besides 
these  two  and  the  heat  afforded  from  without  by  warm  air,  water,  and 
food,  there  are  theoretically  three  other  possible  nutritional  sources. 
These  three  are  the  condensation  of  air  in  the  lungs,  the  liquefaction  of 
gases,  and  the  solidification  of  licjuids.  These  produce  so  small  an 
amount  of  body  heat  that  they  may  be  entirely  neglected.  Reichert 
estimates  that  of  the  two  most  important  means  of  heating  the  body, 
the  chemism  provides  about  90  per  cent,  of  heat,  and  the  friction  only 
about  10  per  cent. 


Fig.  126 


Higher 
Temperature. 


LoTDer 
Temperature. 


Muscular  Chemism . 

Glandutar  Chemis  m 

Nervous  Chemism. 

Friction 

Clothing 

Invironmental  Heat 

Food 

yaso<onstriction 

Central  Deragg^ment 

Atropin. 


Radiation  and  Conduction 

Dermal  Evaporation 

Respiratory  Evaporation. 

Expired  Air. 

Urine 

Feces 

Rest 

Cold  Baching 

^aso- dilation 

Alcohol. 


Human  theiniotaxis.  The  processes  and  conditions  on  the  left  hand  make  for  greater  heat- 
production  or  heat-consers-ation,  while  those  on  the  right  exert  their  influences  toward  less  heat- 
production  or  for  heat-loss. 


Sources  of  heat  from  movement  are  the  circulation,  the  lively  and 
forcible  churning  of  food-masses  in  the  small  intestine  and  by  the  anti- 
peristalsis  in  the  colon  and  rectum,  the  torsion  of  the  costal  cartilages  in 
in.spiration,  and  the  rush  of  air  up  and  down  the  l)ronchi  and  trachea. 
I'yverywhere,  in  short,  that  one  bit  of  tissue  or  of  liquid  moves  against 
another,  heat  from  friction  is  liberate<l,  and  movement,  both  molar  and 
molecular,  is  universal  in  the  organism.  All  these  many  varied  move- 
ments fornl)in('d,  however,  furnish  to  the  body  only  a  small  fraction  of 
its  internally  derived  heat  (Fig.  ]2()). 

The  means  by  which  heat  and  energy  are  lost  or  expended  in  the  body 
may  be  mentioned  under  seven  heads,  the  most  important  coming  first 
in  the  list:     Radiation  and  conduction  from  the  body;  evaporation  of 


METABOLISM 


233 


water  from  the  skin;  evaporation  of  water  from  the  nasal  passages  and 
the  lungs;  expiration  of  the  warmed  air;  excretion  of  the  warm  urine  and 
of  the  warm  feces.  Of  these,  radiation  and  conduction  account  for 
about  73  per  cent,  of  the  heat  lost.  In  other  words,  about  three-quarters 
of  the  heat  made  in  the  body  is  lost  by  warming  its  surroundings,  air, 
water,  bedclothes,  clothing,  chairs,  etc.  Evaporation  from  the  skin 
loses  probably  about  15  per  cent,  of  the  total  quantity  of  heat.  Evapora- 
tion from  the  nasal  passages  and  lungs  expends  not  far  from  7  per  cent, 
of  the  total  heat  lost,  while  about  3  per  cent,  goes  off  in  the  expired  air. 

Fig.  127 


AREA  — CONTENTS  RATIO 


AREA— CONTENTS  RATIO 


This  diagram  shows  that  in  two  animals  of  like  shape  the  smaller  may  have  twice  as  much 
surface-area  (heat-loss)  in  proportion  to  its  contents  (heat-production)  as  the  larger. 

The  term  Therraotaxis,  the  regulation  of  body-heat,  meaning 
literally  "heat-arrangement,"  has  already  been  met  with  in  the  chapter 
on  Protoplasm  (see  page  43),  and  there  indicates  the  reaction  to  heat 
of  the  entire  body  at  once  in  case  of  certain  small  and  simple 
organisms.  As  applied  to  man,  etc.,  its  meaning  is  somewhat  different 
in  that  it  indicates  adjustment  of  parts  of  the  organism  to  special  thermic 
conditions.  The  arrangements  in  the  human  body  by  which  these 
adjustments  are  brought  about  constitute  one  of  the  most  elaborate 
mechanisms  of  the  organism.  By  its  means  the  temperature  is  kept 
constant  despite  the  obvious  wide  ^^riations  in  climate,  food,  dress, 
labor,  etc. 


234 


NUTRITION 


There  are  two  modes  of  regulating  the  amount  and  degree  of  heat  in  a 
homothermous  animal — changing  the  production  and  altering  the  outgo 
of  the  heat.  Since  the  actual  temperature  at  any  time  throughout  the 
bodv  is  the  balance  of  these  two  phases,  regulation  consists  in  alteration 
of  either  or  of  both  in  the  way  circumstances  at  the  time  require.  In 
practice  both  of  these  opposed  processes  are  always  in  action  at  the  same 
time.  When  the  temperature  tends  to  become  too  high,  for  example,  not 
only  is  thermogenesis  (heat-making)  checked  in  one  of  various  ways,  but 
thermolysis  (heat-loss)  is  increased.  When  body-heat  trends  unduly 
downward,  the  two  processes  work  in  just  the  opposite  ways.     In  this 

Fig.  128 


AREA,        78 
CONTENTS,   27 


AREA, 
CONTENTS, 


This  diagram  show.s  tliat  animal  bodies  of  the  same  volume  and  mass  (heat-production) 
may  greatly  differ  in  surface-area  (heat-loss). 

way  the  balance  is  kept  so  perfectly  that  in  health  the  temperature  of 
the  human  body  varies  less  than  2°  from  the  adult  mean  of  about  37°. 
One  sees  the  immediate  working  of  thermotaxis  in  the  involuntary 
shivering  which  often  ensues  on  exposure  to  cold,  and  I^owy  has  shown 
that  this  marked  increase  of  rliytlimic  muscular  contraction  may  even 
double  the  body's  heat-producing  metal)olism.  Another  immediate  proof 
of  the  presence  of  such  a  function  in  the  body  is  seen  in  cold  bathing, 
which,  in  a  normally  reacting  organism  raises  the  temperature.  Again, 
one's  appetite  is  normally  somewhat  less  in  a  hot  day  of  summer  than 
on  a  cold  winter  day,  metabolism  and  heat-profluction  being  thereby 
lessened.     The    arrangements    for   controlling    body-heat    consists,    in 


METABOLISM  235 

general  terms,  of  various  nerve-centers  under  the  supreme  dictation  of 
one  chief  center,  and  of  tissues  and  organs  all  over  the  l)ody  so  coordinated 
that  they  bring  al)out  the  result  re(}uire(l.  In  infants  (and  in  poikilo- 
therms)  the  apparatus  is  not  well  developed. 

We  can  make  the  working  of  the  heat-regulating  mechanism  clearer 
if  we  discuss  its  two  phases  (the  control  of  heat-production  and  that  of 
heat-expense)  separately. 

The  meaxs  of  regulating  heat-production  are  chiefly  the 
increasing  or  decreasing  of  metabolism  and  of  muscular  activity;  only  in 
indirect  ways  can  glandular  activity  be  varied.  In  man  these  means  are 
partly  voluntary,  although  the  "sensations"  underlying  the  voluntary 
acts  required  are  purely  physiological.  In  cold  weather  animals 
"naturally,"  as  we  say,  eat  somewhat  more  food  than  on  warm  days. 
Moreover,  the  human  appetite  then  tends  to  demand  foods  which  are 
large  producers  of  heat  and  energy — in  winter  beefsteak  and  potatoes 
and  bacon  and  hot  rich  soups;  in  summer,  on  the  other  hand,  salads, 
ices,  fruits,  and  "plain  living."  These  same  tendencies  are  seen  in 
whole  racial  diets.  We  find  the  dwellers  of  the  far  North  eating  much 
fat  (combustion-equivalent,  9.3),  while  those  of  the  Tropics  live  on  fruits 
and  cereals  containing  much  liquid  and  waste  cellulose.  It  is  only 
from  habit  that  perhaps  most  people  eat  nearly  as  much  in  warm  weather 
as  in  cold,  for  the  actual  body-demand  is  much  less.  It  is  part  of  the 
heat-regulating  arrangements  (but  how  brought  about  is  unknown), 
that  fats  are  actually  distasteful  on  a  very  warm  day. 

Besides  tending  to  limit  the  general  metabolism  by  thus  decreasing 
its  fuel,  the  organism  automatically  inclines  to  lessen  that  large  percentage 
of  heat  and  energy  which  the  muscles  give  out.  Exertion  tends  to  be 
irksome  in  warm  weather,  partly  it  is  true  because  the  abundant  sweat 
so  occasioned  is  a  source  of  much  discomfort,  but  also  because  muscular 
exertion  is  unnatural  in  great  heat  and  rest  not  only  strongly  desired  but 
also  based  in  physiological  conditions  which  only  the  will  can  overcome. 
The  same  is  true,  but  to  a  less  extent,  perhaps,  in  regard  to  mental 
labor,  although  the  nervous  system  as  compared  with  the  muscles 
produces  but  little  heat.  Muscular  contractions,  however,  always  tend 
to  be  proportionate  to  mental  activity.  Sleep,  as  we  shall  see,  tends 
to  increase  heat-loss  as  well  as  to  limit  heat-production,  and  there  is 
a  natural  tendency  to  sleep  when  the  temperature  is  high. 

In  the  opposite  direction  corresponding  influences  are  at  work.  These 
increase  heat-production  in  cold  surroundings  or  when  heat-loss  (ther- 
molysis) is  excessive.  Under  such  circumstances  one  eats  more  and 
"heavier"  food  and  takes  less  liquid  than  in  the  opposite  condition  of 
environment.  Observing  the  diet  of  luml)ermen  in  the  northern  woods 
in  winter,  one  is  almost  surprised  at  the  large  amounts  of  bread,  butter, 
baked-beans,  bacon,  salt-pork,  and  very  hot  tea  that  are  consumed, 
and  these  diets  often  reach  6000  calories.  Severe  muscular  exertion, 
cold,  and  wet  combine  to  make  the  demand  for  fuel  apparently  exces- 
sive, the  last  two  increasing  the  loss  of  heat  to  a  high  proportion,  while 


236 


NUTRITION 


the  muscular  labor  keeps  up  the  heat-production,  and  by  urgmg  a  rapid 
flow  of  lymph  all  over  the  body,  sustains  the  metabolic  furnace  at  its 
limit  of  vigorous  action.  Contrast  physiologically  with  these  conditions 
those  of  the  city  business-man  who  rides  from  his  home  to  his  office  in 
heated  vehicles,  takes  no  exercise,  worries  more  or  less,  and  who  has 
in  consequence  a  poor  digestion.  This  man  has  no  need  of  increasing 
heat-production  by  eating  much,  for  his  metabolic  fire,  low  and  dull 


Fig.  129 


The  common  so-called  bear-animalcule  (Macrobiotus  Hufelandi),  a  tartigrade,  in  its  active  and 
in  its  dried  (hibernating)  states.  (Greef  and  Plate.)  As  seen  under  the  microscope  in  the  latter 
condition  it  is  not  to  be  distinguished  from  a  speck  of  quartz.  In  this  state  the  animal  w!l  remain 
months  or  even  years,  yet  on  addition  of  water,  it  will  within  an  hour  or  two  oftentimes  resume  its 
complex  animal  acti\Tties.  This,  then,  is  the  extreme  protoplasmic  type  of  hibernation  common 
to  bears,  hedgehogs,  bats,  gophers,  woodchucks,  etc.,  and  voluntarily  attained  for  purposes  of  gain 
by  certain  human  fakirs  of  India.  Eating  no  food,  the  temperature  falls  from  5°  to  13"  C,  the 
heart  slows  and  weakens  its  beat,  respiration  is  greatly  lessened,  and  the  whole  metabolism  is  re- 
duced to  a  minimum.  For  the  two  to  six  months  that  hibernation  lasts,  the  homotherm  becomes 
practically  a  poikilotherm.  In  the  case  of  mammals,  actual  drying  of  the  protoplasm  does  not, 
of  course,  occur,  but  in  botli  alike  the  two  vital  physical  principles,  heat  and  moisture,  are 
lessened.  These  are  the  conditions  of  movement,  and  movement  in  turn  is  the  physical  basis  of 
life.  The  bear  of  the  forests  and  the  bear-animalcule  of  the  eaves-troughs  of  our  houses  alike, 
then,  lower  their  metabolism  for  purposes  of  self-preservation  during  inevitable  long  periods  of 
severe  environmental  stress  which  else  would  kill  them. 

as  it  is,  supplies  all  needs.  But  physiologically  speaking  these  are  two 
distinct  planes  of  living,  if  perfect  metabolism  be  a  just  criterion.  It  is 
easy  to  increase  heat-production,  much  easier  than  to  lessen  it,  for  the 
combustion  in  the  tissues  cannot  be  checked.  If  fuel,  therefore,  be  not 
supplied  them  from  without,  tliey  will  consume  themselves.  As  is  well 
known,  a  ri.se  of  temperature  usually  increases  chemical  action,  so  that 


METABOLISM  237 

if  the  body's  heat  increases  from  any  cause  whatever,  metal)olisni  is 
heightenecl.  In  addition  to  these  modes  of  increasing  heat-production 
there  is  apparently,  in  small  animals  in  particular,  an  influence  exerted 
by  the  nervous  system  directly  on  the  heat-forming  tissues.  This  acts 
especially  on  the  muscles,  and  causes  them  to  increase  the  body-tempera- 
ture without  actual  (visible)  contraction.  This  has  been  called  "chemic 
tone,"  and  in  case  of  muscle  differs  little  from  muscular  tone  (see  below, 
page  390),  but  when  effected  in  other  tissues,  directly  increasing  metab- 
olism, it  is  doubtless  a  portion  of  that  little-understood  system  of  trophic 
influences  (see  page  50).  Various  drugs,  finally,  increase  metabolic 
heat,  these  being  largely  those  like  strychnine,  e.  g.,  which  increase  mus- 
cular tone  or  muscular  activity  of  a  more  obvious  sort. 

Muscular  movements  are  instinctively  employed  by  all  animals, 
homotherms  at  least,  for  increasing  their  temperature.  If  one  compares, 
for  example,  in  this  respect  the  people  on  the  pavements  in  winter  and  in 
summer,  the  difference  in  their  muscular  activities  is  obvious.  Shivering 
is  a  reflex  action  with  considerable  thermogenic  powers. 

The  regulation  of  heat-loss  is  probably  a  more  active  function 
than  is  the  control  of  thermogenesis.  It  is  largely  performed  by  means 
of  vaso-motion  (enlargement  and  narrowing  of  the  arterioles)  in  connec- 
tion with  the  secretion  of  sweat,  both  being  under  the  direction  of  the 
nervous  system.     (See  page  300.) 

When  the  body-temperature  tends  to  become  unduly  low  from  any 
cause,  impulses  are  sent  out  from  the  medulla's  vaso-constrictor  centers 
to  the  arterioles  and  capillaries  of  the  skin  all  over  the  body,  and  these 
thereupon  become  smaller  in  diameter.  This  drives  much  of  the  blood 
then  on  the  surface  into  the  body's  interior.  xA.s  will  be  recalled,  about 
88  per  cent,  of  the  total  heat  lost  is  expended  from  the  skin,  the  amount 
depending  on  the  quantity  of  warm  blood  the  surface  contains.  By  this 
peripheral  vaso-constriction  radiation  and  conduction  are  lessened  as 
well  as  the  production  of  "insensible"  sweat,  by  whose  evaporation 
much  heat  is  lost.  It  is  by  a  too  sudden  and  too  vigorous  action  of  this 
vaso-constrictor  mechanism  that  congestions  of  the  nasal  mucosa,  lungs, 
kidneys,  or  ovaries  are  sometimes  produced.  Normally  the  process 
takes  place  gradually  and  the  circulation  adjusts  itself  so  that  no 
organ  is  harmfully  over-charged  with  blood.  By  this  means  the  latter, 
carrying  so  much  vital  heat  with  it  in  the  course  of  a  minute, 
is  removed  from  the  surface,  whence  that  heat  would  be  partly 
lost.  Exposure  to  cold  causes  the  skin  to  become  blanched,  but  if  it  be 
excessive  the  nerves  or  muscles  of  the  arterioles  or  both  are  paralyzed 
and  the  blood-vessels  expand  widely  under  the  pressure  from  the  heart, 
making  the  skin  red.  Chronic  alcoholism,  because  of  its  continued 
surface  vaso-dilating  effect,  has  the  same  influence  on  the  skin.  Owing 
to  the  reciprocal  action  between  the  skin  and  the  kidneys,  the  vaso- 
constriction in  the  former  tends  to  increase  the  flow  of  urine.  Only 
1  or  2  per  cent.,  however,  of  the  body's  heat  is  given  off  in  the  urine,  so 
that  this  opposing  eifect  counts  init  little  in  increasing  thermolysis. 


238  XUTRITIOX 

^'oliintarily  the  loss  of  heat  is  decreased  by  man  by  wearing  more 
clothing  or  furs,  which  besides  being  themselves  non-conductors  of  heat, 
help  to  keep  a  layer  of  "dead,"  non-conducting  air  about  the  body. 
In  the  lower  animals  this  fact  is  obvious,  many  animals  having  two  suts 
of  fur  or  of  feathers  of  very  different  degrees  of  "warmth." 

When  the  body-heat  becomes  or  tends  to  become  abnormally  high, 
in  general  the  opposite  physiological  movements  occur.  The  dermal 
blood-vessels  under  the  influence  of  the  vaso-motor  centers  dilate,  and 
much  more  blood  being  then  forced  into  the  skin,  radiation  and  conduc- 
tion increase  and  sweat  is  more  freely  poured  out.  The  latter  not  only 
aids  thermolysis  by  evaporation,  but  it  makes  conduction  and  radiation 
more  active  bv  increasino;  the  conductivity  of  the  skin.  It  acts,  also, 
and  more  importantly,  by  pouring  the  water  to  be  evaporated  outside 
the  oily  and  ill-conducting  epidermis,  it  being  the  sebum  and  not  the  sweat 
which  contains  fat.  This  dermal  vaso-dilatation  is  probably  the  most 
active  means  of  heat-regulation,  and  it  serves  as  a  prompt  and  vigorous 
agent  in  expending  surplus  heat.  Because  of  its  failure  in  fever,  owing 
to  some  disturbance  in  the  medullary  centers,  the  temperature  rises;  this 
increases  metabolism,  which  in  turn  raises  the  heat  still  more.  Many 
other  influences  at  different  times  act  in  a  similar  way,  chief  among  these 
being  bacterial  irritations  from  toxins.  Sometimes  during  fever  sweat 
is  secreted,  but  it  is  exuded  on  a  cool  surface  ("cold  sweat")  and  usually 
under  conditions  which  largely  prevent  its  proper  antipyretic  effect.  It 
is  sweat-secretion  of  this  purely  "nervous  origin,"  unaccompanied  by 
dermal  vaso-dilatation,  which  comes  from  some  emotions,  especially  terror. 

With  the  reflex  vaso-dilatation  in  the  skin  may  go  the  other  more 
voluntary  conditions,  already  noted,  useful  for  the  reduction  of  body- 
heat,  such  as  frequent  bathing  and  the  removal  of  clothing.  Any 
circumstance,  in  short,  which  will  help  to  expose  to  a  cooler  environment 
(air  or  water)  a  larger  amount  of  body-heat  than  before  serves  to  cool 
the  body,  heat-production  being  at  the  same  time  reduced  reflexly, 
instinctively,  or  voluntarily  on  a  basis  of  instinct  or  of  comfort. 

The  Tiier.motactic  Nerves. — The  neural  mechanism  of  heat- 
regulation  is  as  yet  in  its  details  not  very  well  known.  There  is  good 
functionary  evidence  that  there  is  something  like  a  reflex  arc  for  this 
thermotactic  purpose.  The  tissues  have  means  of  sending  information 
concerning  their  thermic  condition  to  the  brain,  which  thereupon  sets 
in  motion  the  regulating  mechanism  in  the  direction  required,  either 
to  stimulate  the  tissues  (especially  the  muscles)  to  produce  more  heat  or 
to  stimulate  the  skin  to  lose  more  heat,  or  vice  versa.  As  will  be  seen 
more  fully  in  the  chapter  on  the  Sense  Organs,  there  are  minute  spots 
scattered  through  the  skin,  some  of  which  respond  to  stimulation  by 
heat  and  some  to  siimulation  by  cold.  'J'he  ];r(sumption  is  allowable, 
at  least,  that  besides  afl'ording  the  animal  protection  from  external  heat 
or  cold,  the  nerve-end  organs  within  the.se  spots  originate  afferent 
impulses  which  actuate  a  thermotactic  center,  some  knot  of  neurones 
which  bv  its  connection  with  the  otiicr  centers  of  the  brain  controls  all 


METABOLISM  239 

these  various  processes  of  heat-production  and  of  heat-loss.  Xo  such 
action  of  the  heat-  and  cold-spots  has  been  actually  demonstrated, 
however,  so  that  this  interestin<j  matter  must  remain  only  a  fair  pre- 
sumption until  its  truth  has  been  actually  proved.  What  evidence  there 
is  is  in  its  favor. 

About  the  heat-center  or  -centers  there  is  more  definite  information. 
It  is  apparently  located  in  the  caudate  nucleus  of  the  corpus  striatum. 
Puncture  of  this  little  area  of  the  interior  of  the  brain  even  with  a  fine 
needle  causes  in  animals  a  marked  rise  of  body-temperature.  Ott 
found  another  and  more  likely  thermogenic  center  in  the  tuber  cinereum 
of  the  optic  thalmus,  and  this  has  been  corroborated.  This  latter  region 
of  the  brain  is  closely  connected  with  the  vaso-motor  apparatus,  for 
puncture  of  its  anterior  part  causes  a  marked  fall  of  blood-pressure  by 
vaso-dilatation.  The  increase  of  the  heat-production  which  then  follows 
is  probably  brought  about  b}  radiation  of  the  nerve-influence  into  the 
adjacent  motor  paths.  This  would  cause  an  innervation  of  the  muscles 
and  a  lise  in  their  trophic  heat-production.  Evidence  of  a  probable 
thermolytic  center  is  more  vague. 

^Miatever  the  exact  neural  mechanism  of  thermotaxis,  it  does  not 
reach  its  full  development  in  the  human  animal  until  about  the  tenth 
year.  We  see  evidence  of  this  very  often  in  the  rapid  rise  of  temperature 
in  young  children  from  causes  so  slight  that  they  would  not  at  all  influence 
the  adult  temperature. 

Other  Forms  of  Energy-expense  in  which  katabolism  manifests  itself 
are  those  other  than  growth  and  repair,  secretion,  and  heat,  which  have 
now^  been  discussed.  They  are  mainly  muscular  and  nervous  force. 
IMuscular  power  is  discussed  in  a  chapter  by  itself  and  nervous  force 
with  the  functions  of  the  nervous  system.  These  need  only  mention  in 
this  place  for  the  sake  of  systematic  completeness. 

There  remains  under  the  head  of  katobolism  to  briefly  describe  the 
excretory  processes  as  such  and  the  harmful  substances  to  which  these 
important  processes  give  rise.  This  is  comprised  under  the  general 
term  excretion,  the  latter  phase  of  external  nutrition. 

Excretion. — The  excretion  of  substances  of  no  further  use  to  the  organ- 
ism is  an  indispensable  part  of  nutrition.  They  are  mostly  of  such  a  na- 
ture that  they  would  poison  the  organism  and  promptly  cause  its  destruc- 
tion did  they  remain  within  it.  The  five  familiar  sorts  of  food-material 
(protein,  fat,  carbohydrate,  salts,  and  water)  partake  more  or  less  in 
the  structure  of  the  tissue-molecules,  are  sooner  or  later  katabolized,  and 
their  elements  at  least  sent  out  of  the  body  either  by  the  kidneys,  the  lungs, 
the  rectum  (including  the  liver's  contribution),  or  the  skin.  Minute 
quantities,  relatively,  are  also  excreted  by  the  reproductive  and  nasal 
organs,  and  as  the  dermal  appendages,  hair  and  nails,  but  these  are 
negligible  otherwise  than  in  this  mention.  The  most  important  of  the 
actual  end-products  of  katobolism  excreted  by  man  are  urea,  carbon 
dioxide,  and  water,  these  together  representing  the  ultimate  waste  of  the 
three   basal   "proximate  principles,"   protein,  fats,   and   carbohydrates 


240  NUTRITION 

(but  not  respectively).  The  salts  and  the  water  ingested  are  mostly- 
excreted  in  unchanged  condition.  In  our  knowledge  of  the  katabolism 
of  proteids,  fats,  and  carbohydrates  there  are  as  yet  large  gaps,  and  hence 
our  description  of  this  must  be  at  present  partly  conjectural;  indeed,  in 
some  of  its  aspects  largely  so.  We  shall  do  best,  perhaps,  by  keeping 
out  attention  mainly  on  the  nitrogen,  the  carbon-dioxide,  and  the  water 
of  katabolism.  For  practical  convenience,  however,  we  must  describe 
this  general  katabolic  excretion  under  the  heads  of  the  respective  ex- 
creting organs :  the  kidneys  excreting  urine,  the  lungs  carbon  dioxide  and 
water,  the  rectum  feces,  the  liver  bile,  and  the  skin  also  water  and 
carbon  dioxide.  Aside  from  the  value  of  metabolic  theory,  these  excretory 
menstrua  have  very  large  practical  importance,  and  hence  their  respective 
compositions  and  modes  of  excretion  from  the  body  must  be  thor- 
oughly understood. 

The  Urine. — The  urine  excretes  about  94  per  cent,  of  the  nitrogen 
involved  in  proteid  katabolism,  3  or  4  per  cent,  of  the  katabolic  carbon, 
about  one-half  of  the  excreted  water,  and  a  large  part  of  the  inorganic 
salts  used  in  the  body.  The  nitrogen  comes  partly  from  the  wasting 
tissues,  but  in  varying  proportions  also  from  the  circulating  proteid. 
The  carbon  in  the  urine  comes  to  a  slight  extent  from  the  carbo- 
hydrates and  fats  of  the  tissues  and  the  "food"  still  circulating  in  the 
blood,  but  mostly  from  the  degenerating  proteid  molecules  of  the  cells. 
The  water  is  larely  ingested  as  such,  but  about  one-fourth  part  of  it 
appears  to  be  liberated  or  even  compounded  from  the  fats  and  car- 
bohydrates katabolized  in  the  body. 

First,  as  to  the  nitrogen.  As  we  saw  above,  the  proteids  absorbed 
from  the  intestine  pass  into  the  latter's  epithelium  as  proteoses  or  pep- 
tones, or  else  (Bayliss  and  Starling)  this  epithelium  constructs  the 
peptones  from  the  amido-acid  products  of  tryptic  zymolysis.  These 
cells  or  the  endothelium  of  the  capillaries,  or  both,  probably  dehydrate 
the  proteoses  or  peptones  and  change  them  over  into  the  serum-albumin, 
serum-globulin,  etc.,  of  the  blood.  As  such  native  proteids,  then,  the 
protein  material  from  the  gut  passes  through  the  portal  vein  on  its  way 
to  the  liver,  first  soaking  through  the  spleen.  There  is  no  evidence 
that  any  of  the  circulating  or  food-proteid  is  stopped  by  the  liver  except 
when  fat  and  carbohydrate  are  entirely  lacking  in  the  food.  In  this  case, 
owing  to  the  energetic  demand  of  the  body  for  these  two  proximate 
principles  to  furnish  heat  and  power,  some  of  the  food-proteid  from  the 
intestine  may  be  retained  and  changed  into  these  substances  along 
with  urea.  This  urea-part  of  the  suggested  anabolism,  however,  woukl 
represent  an  unlikely  waste  of  precious  nitrogenous  material,  unless, 
indeed,  the  tissue-proteids  and  the  circulating  food-proteids  are  so  closely 
allied  that  their  separation  is  impossible.  For  this  possible  formation 
of  fat,  glycogen,  and  urea  from  protein  in  the  liver,  Dubois  suggests  the 
following  cfiuation,  not  as  just  what  actually  takes  place,  but  as  something 
similar  perhaps  to  the  reaction.  (The  proteid-formula  is  Lieberkiihn's 
and  also  Loew's  conjecture  for  albumin.) 


METABOLISM  24  J 

4(C,,H„,N,8SO,,)  +  68H,0  =  SCQ^HiotOe)  +  12(CeHiA)  +  36(CON,H,)  + 
Proteid  +     Water    =         Fat  +     Glycogen        +  Urea  + 

4(H,S03)    +      15(C0,) 
Sulphurous  acid  +  Carbon  dioxide. 

The  food-derived  or  circulating  proteid  of  the  portal  vein,  unless 
excessive,  probably  goes  through  to  the  tissues  sooner  or  later  and  largely 
to  the  muscles,  where  it  is  stored  as  part  of  the  tissue  in  the  way  suggested 
vaguely  below  (page  3S3).  Voit  supposes,  however,  that  this  food- 
proteid  does  not  become  an  intimate  part  of  the  tissue  molecules  in  this 
simple  way.  The  production  of  urea,  made  at  the  rate  of  thirty-two 
grams  daily,  cannot  begin  in  the  liver,  as  Schafer  shows,  because  suffi- 
cient oxidation  to  prepare  its  precursors  does  not  occur  in  that  organ,  nor, 
indeed,  elsewhere  than  in  muscle,  the  chief  tissue  of  bodily  activity. 
Only  a  little  urea,  however,  is  produced  in  the  muscles,  the  larger  part 
of  it  by  far  being  the  product  of  the  liver.  If  the  ureagenic  process 
starts  in  the  muscles  and  is  finished  in  the  liver,  what,  then,  are  the  inter- 
mediate steps,  and  especially  in  what  form  does  it  pass  from  the  muscle 
to  this  great  gland?  Gaglio  found  lactic. acid  in  the  blood  as  a  con- 
tinual constituent,  and  sarco-lactic  acid  is  known  to  be  a  product  of 
muscular  action.  Schafer  supposes,  therefore,  that  ammonium  lactate  is 
the  form  in  which  the  product  of  proteid  katabolism  goes  to  the  liver, 
there  to  be  converted  (perhaps  by  way  of  creatin  as  an  intermediate  stage) 
into  urea,  in  which  form  the  kidneys  excrete  it.  Certain  hexone  bases 
and  alloxuric  bodies  {e.g.,  uric  acid  and  the  xanthins)  may  be  other  in- 
termediate steps.  As  to  the  chemistry  of  this  process,  the  hypothesis  of 
Drechsel  meets,  perhaps,  with  most  frequent  acceptance.  His  supposition 
starts  with  ammonium  carbonate.  By  losing  one  molecule  of  water  this 
becomes  ammonium  carbamate,  and  the  latter  by  giving  up  another 
water-molecule  becomes  urea. 


/0(NH,) 

/NH., 

/NH, 

('NH3,\ 

c=o 

C=0 

C=0 

CO2, 

\0(NH,) 

\0(NH,) 

\NH., 

^HjU  / 

Ammonium  carbonate. 

Ammonium  carbamate. 

Urea. 

Ultimate  products, 

The  urea,  CONjH^,  as  the  bearer  of  about  six-sevenths  of  the  nitrogen 
excreted  from  the  body  and  of  part  of  the  carbon,  is  of  considerable 
importance  in  all  metabolic  work.  From  twenty  to  seventy  grams,  in 
round  numbers,  are  excreted  daily,  the  average  amount  on  a  mixed  diet 
being  thirty-two  grams,  which  contain  about  fifteen  grams  of  nitrogen. 
The  two  extremes  given  above  are  those  of  a  bread-diet  and  an  abundant 
lean-meat  diet  respectively.  Urea  (carbamide)  is  a  diamide  of  carbonic 
acid,  as  was  indicated  above.  It  is  freely  soluble  in  water,  but  insoluble 
in  ether,  has  a  bitterish,  cooling  taste,  and  forms  in  slender,  four-sided 
prisms  with  shiny  surfaces  and  pyramidal  ends.  Heated  with  water  it 
gives  off  ammonia  and  becomes  converted  into  ammonium  carbonate. 
jNIammalian  muscle  contains  1  or  2  per  cent,  of  urea.  Its  amount  in 
urine  is  commonly  determined  by  the  method  of  Knop  and  Hiifner, 
which  consists  of  decomposing  it  with  sodium  hypobromite  in  the 
16 


242  NUTRITION 

presence  of  caustic  alkali ;  the  latter  absorbs  the  carbonic  dioxide  and  the 
nitrogen  is  collected  in  a  graduated  tube.  From  the  amount  of  this 
nitrogen  the  quantity  of  the  urea  decomposed  is  calculated,  every  gram 
of  urea  giving  37.1  cubic  centimeters  of  nitrogen  by  this  method.  The 
nitrate  and  oxalate  of  urea  have  importance  in  examinations  for  urea. 

The  non-nitrogenous  portion  of  the  product  of  the  katabolic  process 
in  proteid  is  ultimately  oxidized,  like  other  such  substances,  to  carbon 
dioxide  and  water,  perhaps  by  way  of  glycogen  or  dextrose.  The  sul- 
phur probably  goes  into  the  sulphates  of  the  urine  and  of  the  feces. 
Such  are  the  hypotheses  which  at  present  seem  rather  more  probable 
than  others  to  many  biochemists  and  physiologists. 

The  water  of  the  urine  varies  in  amount  largely  at  different  times, 
but  on  the  average  perhaps  runs  within  200  c.c.  of  1^  liters  daily.  It  is 
derived  from  several  sources.  Part  (perhaps  two-fifths)  is  ingested 
directly  as  cold  or  warm  drinks ;  part,  about  two-fifths,  is  ingested  mixed 
chemically  or  mechanically  with  the  food;  the  other  fifth  is  produced 
anew  by  the  body-katabolism.  (The  water  excreted  by  the  kidneys  is 
only  about  half  that  excreted  by  the  body,  most  of  the  remainder  going 
out  through  the  skin,  and  half  a  liter  or  less  through  the  respiratory 
tubes.)  The  ingested  water  so  far  as  known  is  not  altered,  unless  it  be 
mechanically,  for  there  is  no  evidence  that  any  of  it  is  broken  up,  nor 
that  it  combines  chemically  with  any  element  of  protoplasm.  If  it  did 
so,  however,  we  could  not  know  it,  and  the  possibilities  of  its  chemical 
reactions  in  the  metabolism  are  very  many.  The  water  actually  pro- 
duced in  the  body  is  made  by  the  oxidation  of  hydrogen.  The  fats 
especially  are  productive  water-formers,  for  they  contain  much  more 
hydrogen  than  is  necessary  to  satisfy  their  oxygen,  and  are  therefore 
fuel  of  the  best  t}^e.  The  empirical  formula  of  stearin,  for  example,  is 
C.^HjjfjOg,  which  shows  at  a  glance  the  large  amount  of  hydrogen  with 
a  maximum  combustion-value  available  for  oxidation,  the  oxygen  for 
which  respiration  supplies.  The  carbohydrates  and  the  proteids  like- 
wise contribute  to  the  water-making,  the  former  much  more  largely  than 
the  latter.  The  water  is  produced  largely  in  the  muscles  from  the 
combustion  of  glycogen  and  dextrose,  but  also  wherever  carbohydrate  and 
fatty  food  or  tissue  is  katabolized  w^th  the  absorption  of  oxygen.  The 
oxidative  process  probably  occurs  to  some  extent  everywhere  in  the  site 
of  the  former  molecules.  The  katabolism  precedes  the  oxidation  rather 
than  vice  versa,  for  oxygen  has  no  power  to  break  down  the  protoplasmic 
molecule;  it  has  however,  great  chemical  affinity  for  simple  combustibles 
which  are  free  to  combine  with  it. 

The  composition  of  the  urine  is  a  matter  of  much  importance 
theoretically  and  practically,  for  it  is  this  liquid  which  offers  the  best 
chance  to  learn  what  goes  on  chemically  at  difi'erent  tim(>s  under  a  multi- 
tude of  various  conditions,  dietetic,  meta])()lic,  and  })atliologic,  within 
the  hidden  ti.ssues.  The  urine  is  able  still  to  teach  the  physiologist 
much  more  even  than  it  has  taught  him  about  metabolism,  and  the 
physician  very  much  about  the  condition  of  his  patient. 


METABOLISM 


243 


A  complete  list  of  all  the  substances  found  regularly  in  normal  urine 
would  be  very  long,  but  among  them  are  the  following  dissolved  in  the 
water:  Urea,  uric  acid,  hippuric  acid,  creatinin,  urochrome,  urobilin, 
uroerythrin,  hematoporphyrin,  chromagens,  dextrose,  isomaltose,  vola- 
tile fatty  acids,  xanthin,  heteroxanthin,  paraxanthin,  hypoxanthin, 
guanin,  adenin,  amido-acids,  phenol-sulphuric  acid,  cresol-sulphuric 
acid,  etc.,  inosit,  glycuronic  acid,  acetone,  cholesterin,  lecithin,  sulphates 
and  acid-sulphates  of  sodium  and  potiissium,  phosphates  of  sodium, 
potassium,  calcium,  and  magnesium,  chlorides  of  sodium,  calcium,  and 
potassium,  sulphocyanide  of  potassium,  lactic  acid,  iron,  hydrogen 
peroxide,  carbon  dioxide,  ammonia,  and  enzymes.  Most  of  these  would 
be  reported  in  chemical  analyses  as  traces  merely.  The  important  and 
measurable  constituents  are  given  in  the  following  table : 


Average  Composition  in  Grams  of  a  Day's  Urixe. 


Important  constituents. 


Total  amounts  (c.c.) 


Organic 


fUrea,  CON^H,  .      .      . 

I  Uric  acid,  etc.  (xanthins) 

1  Creatinin,  C^OXaH- 

I  Pigment,  etc.     . 

I  Ammonia,  NH., 

L  Hippuric  acid,  CyOa.XHg 

fiso 

I  Na.,0 


I  CaO 
Inorganic  -{  MgO 
I  CI     . 
I  SO3   , 

I  P,6 


Mixed 

Flesh 

Bread 

diet. 

diet. 

diet. 

1500 

1672 

1920 

33 .  IS 

67.200 

20.600 

0..5.5 

1 .  398 

0.253 

0.91 

2.163 

0.961 

10.00 

0.77 

0.900 

0.400 

0.40 

*2.50 

3.308 

1.3i4 

*11.09 

3.991 

3.923 

*0.26 

0.328 

0.339 

*0.21 

0.294 

0.139 

7.50 

3.817 

4.996 

2.01 

4.674 

1 .  265 

3.16 

3.437 

1.658 

*  Calculated  as  the  metal  and  not  as  the  oxide. 

The  above  table  (altered  from  one  by  MacLeod  after  analyses  given 
by  Parkes  and  Bunge)  shows  how  wide  is  the  variation  in  the  composi- 
tion of  the  urine  with  different  diets.  The  urea,  for  example,  in  1920  c.c. 
of  urine  excreted  on  a  bread-diet  was  little  more  than  30  per  cent,  of 
its  amount  when  all  the  food  was  meat,  although  in  the  latter  case  the 
amount  of  the  urine  was  248  c.c.  less  in  quantity.  This  is  a  constant 
variation,  for,  other  things  equal,  a  meat-diet  gives  rise  to  a  small  amount 
of  concentrated  urine,  the  water-producing  factors  of  the  mixed  and 
largely  carbonaceous  diets  not  being  present.  The  average  amount 
secreted  is  about  1500  c.c.  (ranging  from  1200  to  1700  c.c),  or  about 
1  c.c.  each  hour  for  every  kilo  of  body  weight.  Women  excrete  about  200 
c.c.  less  than  men  daily  and  children  per  kilo  of  weight  70  per  cent, 
more.  The  amount  is  increased  by  drinking  liquids  or  eating  a  large 
amount  of  proteid,  by  lack  of  respiratory  oxygen,  rise  of  renal  blood- 
pressure,  ingestion  of  a  large  amount  of  "extractives,"  vaso-constriction 
in  the  skin,  various  drugs,  diabetes,  and  by  some  nervous  derangements. 


244 


NUTRITION 


Urine  is  a  yellowish  clear  liquid  of  a  specific  gravity  of  from  1017  to 
1020,  acid  in  reaction,  with  a  bitter  saline  taste  and  a  characteristic 
odor.  For  short  times  during  the  day,  especially  after  meals,  the 
reaction  may  be  slightly  alkaline,  but  the  normal  mixed  urine  of  the 
twenty-four  hours  appears  to  be  always  somewhat  acid  due  to  the  acid 
phosphates  of  sodium,  calcium,  and  potassium.  The  specific  gravity  is 
normally  in  general  inverse  proportion  to  the  quantity;  to  find  approxi- 
mately the  number  of  grams  of  dissolved  solids,  multiply  the  last  two 


Fig.  130 


The  circulation  about  the  convohited  tubules.      Observe  the  contrast  between  the  straight 
and  hirge  arterioles  and  the  tortuous  veinlets.      (Bates.) 

figures  of  the  .specific-gravity  num})er  by  2.3  (Trapp).  In  fever,  because 
usually  httle  liquid  and  food  are  taken  and  becau.se  in  con.scquence  the 
ti.ssues  katabolize  them.selves,  the  urine  is  scanty,  highly  coloi'ed,  and  of 
high  specific-gravity.  The  yellowness  of  urine  is  due  to  urochrome  and 
to  a  slight  extent  to  urobilin,  especially  in  disease,  while  other  pigments 
are  present  in  small  amounts  under  certain  conditions:  uroerythrin, 
hematoporphyrin,  and  certain  chromogens.  The  odor  of  urine  is  due 
to  tlie  contained  aromatics  (phenol-skatoxyl,  kresol,  etc.),  combined  with 


METABOLISM 


245 


about  0.8  gram  per  liter  of  dissolved  ammonia.     The  taste  is  largely 
that  of  sodium  chloride  plus  a  bitterness  whose  source  is  complicated. 

The  excretion  of  urine  from  the  renal  epithelium  to  the  distal 
end  of  the  urethra  involves  both  the  secretory  function  of  protoplasm 
and  a  complicated  series  of  muscular  and  recoiling  movements;  the  latter 
part  of  the  process,  the  expulsion  of  the  urine  from  the  bladder,  is  speci- 
fied as  micturition. 

Fig.  131 


Descending  limb  \ 
of  Hcnle's  loop,  j 


Diagram  of  a  uriniferous  tubule,  suggesting  vaguely  the  varieties  of  epithelium  composing 
it:  A,  flattened  cells  with  oval  nuclei;  B,  polyhedral,  striated  cells;  C,  polyhedral,  striated  cells, 
but  with  their  nuclei  near  the  lumen  of  the  tubule;  D,  polyhedral  cells  striated  only  in  the  outer 
part  and  with  flattened  and  angular  nuclei;  E,  variable  cells:  polyhedral,  columnar,  angular 
with  short  processes,  and  fusiform;  F  and  G,  columnar  and  variable  cells;  H<  angular  cells  with 
conspicuous  rodded  striations.      (Gray.) 


The  first  matter  to  be  examined  into,  then,  is  the  manner  in  which 
some  of  the  numerous  complex  substances  recently  enumerated  are  taken 
from  the  blood-stream  and  collected,  dissolved  in  water,  in  the  receiving 
hilum  of  the  kidney.  Not  until  all  tlie  secrets  of  protoplasmic  secretion 
are  unravelled  will  the  details  of  these  versatile  chemical  reactions  be 
known,  and  here  as  elsewhere  in  discussing  secretion  it  is  only  the  gross 


246 


NUTRITION 


Fig.  132 


processes  and  the  general  results  which  can  be  described.  The  illustra- 
tion shows  the  various  parts  and  twists  of  the  uriniferous  tubule,  but  it 
fails  to  describe  their  respective  functions  and  what  each  of  the  several 
varieties  of  epithelium  making  up  the  tubule  contributes  to  the  urine's 
complex  composition. 

Few  subjects  in  physiology  have  been  more  actively  discussed  than 
this,  the  matter  resting  on  two  basal  presumptions,  nearly  opposite  in 
theory,  concerning  renal  secretion.  These  presumptions  are  still  known 
as   the   theories   of   Bowman   and   of  Ludwig   respectively.     Bowman 

supposed  that  the  protoplasm  of  the  cap- 
sule named  for  him,  largely  by  virtue  of 
its  own  secretory  powers,  took  from  the 
capillary  blood  the  salts  and  the  water  of 
the  urine;  and  that  the  varied  epithelium 
of  the  different  tubular  parts  farther  down 
added  the  organic  constituents,  the  urea, 
hippuric  and  uric  acids,  and  the  rest; 
Heidenhain  has  added  much  support  to 
this  theory.  Ludw^ig's  hypothesis  was 
more  mechanical  so  far  as  the  working 
of  the  glomeruli  are  concerned,  for  he 
maintained  that  these  tiny  organs  are 
little  more  than  organized  filters  which 
by  physical  means  take  the  urine  in  a 
dilute  form  out  of  the  stream  of  blood  to 
be  condensed  later  by  the  absorption  from 
it  of  water  in  the  epithelial  walls  of  the 
devious  tubules.  The  research  of  Cushny 
and  others  makes  them  suppose  with 
Ludwig  that  the  water,  salts,  and  urea 
pass  from  the  glomeruli  into  the  tubules, 
but  that  part  of  the  salts  and  of  the  water 
pass  from  the  latter  again  into  the  circula- 
tion. (See  the  figure  opposite  diagram- 
ming these  three  theories. )  A  compromise 
which  recent  work  impels  makes  it  likely 
that  urinary  excretion  is  accomplished  by  both  mechanical  filtration 
and  by  vital  secretory  action  in  the  glomerulus,  but  that  the  epi- 
thelium of  the  tubules  contributes  perhaps  numerous  unknown  sub- 
stances to  the  urine.  Here,  as  in  the  other  cases,  we  may  safely  say 
that  there  Ls  mechanical  filtration  surely  enough,  but  that  the  filter  is 
alive  and  selects  what  it  shall  let  pass  and  passes  nothing  else  so  long 
as  it  is  normal.  The  trend  of  recent  work  has  been  to  prove  directly 
that  the  "roflrlofl"  or  striped  epitlielium  of  the  tulniles  secretes  products 
(such  for  example  as  uric  acid)  into  them;  urea  also  may  be  seen  to 
collect  in  vacuoles  in  the  epithelial  cells,  the  former  "bursting"  after  a 
while,    llie  glomerulus  acts  in  a  manner  and,  occasionally  at  least,  under 


The  relation  of  the  blood-capil- 
laries to  the  convoluted  tubule  in  the 
frog's  kidney.  The  erythrocytes  in 
the  capillary  close  to  the  outer  side 
of  the  tubular  epithelium  and  the 
nerve  fibers  supplying  the  two  last 
are  ob\nous.      (Smirnow.) 


METABOLISM 


247 


conditions  in  whicli  no  mere  passive  filter  eould  do  the  work.  Sometimes, 
for  example,  the  glomerulus  eontinues  its  excretion  when  the  blood's 
pressure  is  below  that  in  the  tubules,  while  the  osmotic  pressure  of  the 
secreted  urine  is  several  times  that  of  the  blood,  the  current  of  urine 
none  the  less  passing  in  the  normal  direction  against  this  great  balance 
of  resistances.  There  is  nothing  present  but  the  epithelium  to  supply  this 
large  amount  of  energy.  In  what  way  the  varieties  of  epithelium  up 
and  down  the  tubules  correspond,  if  at  all,  to  the  various  constituents  of 
the  urine,  we  do  not  at  all  know.  It  is  likely  that  the  "salts"  and  much 
of  the  water  enter  the  apparatus  through  the  glomerulus,  and  that  the 
organic  constituents  are  added  from  the  blood  under  much  lower  press- 
ure by  the  protoplasm  farther  down.  The  mechanical  phases  of  the 
process  (and  they  may  be  of  considerable  importance)  proceed  undoubt- 
edly in  the  jNIalpighian  body. 


Fig.  133 


Bowman's. 
Heidenhain's, 


Lud wig's. 


Cushny's. 


Blood- 


Urea.  •«- 


Albumen  <3ndsu^ar.  -*— 


Theories  of  urinary  secretion. 


^Miich  of  the  cells  supply  the  kidney's  supposed  internal  secretion 
(see  page  228)  is  not  known.  It  may  serve  not  only  to  direct  in  some  way 
whatever  proteid  katabolism  goes  on  in  the  renal  epithelium,  but  also 
to  adjust  the  blood-pressure  of  the  organ  in  the  directions  local  needs 
require,  acting  in  this  perhaps  in  connection  with  the  vasomotor  centers. 

The  amount  of  urine  excreted  varies  with  the  amount  of  blood  passing 
through  the  renal  capillaries  as  well  as  on  the  pressure  of  this  blood. 
Heidenhain  showed  this  by  ligating  the  renal  vein.  This  stopped 
altogether  the  secretion  of  urine,  although  the  glomerular  blood-pressure 
was  much  increased.  Diuretics  act  in  various  ways :  Digitalis  increases 
the  heart's  work  and  so  forces  more  blood  through  the  renal  vessels. 
Exposure  of  the  skin  to  cold  acts  partly  in  the  same  way  as  digitalis,  the 
increase  of  the  general  blood-pressure,  owning  to  peripheral  vaso-constric- 


248 


XUTRITiax 


tion,  being,  however,  more  conspicuous.  Some  diuretics,  such  as  caffeine, 
seem  to  act  on  the  renal  epithehum.  Others  act  directly  on  the  renal 
vessels,  increasing  the  blood-pressure  locally. 

The  DiscH-UiGE  of  Urixe. — ^The  urine  collects  in  the  hilum  of  the 
kidney  under  a  pressure  (in  the  dog)  of  60  mm.  of  mercury.  The  ducts 
of  Bellini  enter  through  the  p^Tamids  very  obliquely  in  such  a  way  that 
the  greater  the  pressure  within  the  hilum  the  more  tightly  are  their 
orifices  closed.  This  arrangement  acts  as  a  perfect  automatic  valve  to 
prevent  regurgitation  of  the  urine  upward  into  the  collecting-tubes  and 
consequent  interference  with  the  secretory  process  of  the  tubules  in  cases 


Fig.  134 


of  impacted  calculus,  etc.  From  the  hilum  the  urine  passes  in  a  contin- 
uous trickle  through  the  pelvis  of  the  kidney  into  the  ureter.  This  tube, 
composed  of  fibrous,  muscular,  and  mucous  coats,  is  about  43  cm.  long 
and  4  or  5  mm.  in  diameter,  and  connects  the  kidney  with  the  urinary 
bladder.  The  muscle  is  of  the  smooth  variety,  the  fibers  running  both 
longitudinally  and  circularly.  It  is  supplied  with  sensory  and  motor 
nerves.  The  former  are  aseful  perhaps  in  adapting  the  vigor  of  the 
peristalsis  to  the  resistance  the  latter  has  to  ovecome,  as,  e.fj.,  in  passing 
calculi  through  it.  In  man  three  sorts  of  forces  seem  to  help  in  the 
passage  of  urine  through  the  ureters:  the  secretory  pushing  "force  from 


METABOLISM  249 

behind,"  peristalsis,  and  gravity.  To  Engelmann  we  owe  our  knowledge 
of  the  muscular  movements  of  the  ureter.  He  found  that  true  peri- 
staltic waves  pass  from  the  kidney  to  the  bladder  every  half-minute  on  the 
average  at  the  rate  of  2  or  3  cm.  per  second  (the  muscle  thus  resting 
half  or  two-thirds  of  the  time).  Cases  of  non-closure  of  the  bladder-walls 
during  development  (ectopia)  show  that  the  urine  spirts  into  the  bladder 
at  about  half-minute  intervals.  The  activity  (frequency  and  power) 
of  these  movements  is  increased  by  additional  resistance  in  the  tube. 
The  musculature  of  the  ureter  is  classed  by  the  myogenists  as  "auto- 
matic," as  if  dependent  largely  on  food-supply  rather  than  on  immediate 
and  continuous  nervous  actuation.  In  this  respect  the  ureter  is  like  the 
heart,  intestine,  etc.,  each  ureter  being  practically  one  continuous  muscle- 
fiber.  On  the  neurogenic  theory,  resident  nerve-cells  control  all  these 
activities. 

The  bladder  serves  the  double  function  of  a  reservoir  and  an  expelling 
viscus.  The  adult  male  bladder  holds  normally  about  600  c.c,  but  it 
may  contain  well  enough  three  times  that  quantity.  This  distention 
cannot,  however,  be  said  to  be  quite  normal,  being  more  or  less  harmful. 
The  bladder  might,  but  injuriously,  accommodate,  therefore,  a  whole 
day's  urine,  but  it  is  ordinarily  emptied  when  containing  400  or  even 
300  c.c.  It  performs  its  expelling-function  by  means  of  the  elastic  and 
muscular  tissues  of  its  walls,  aided  by  abdominal  pressure.  The  ureters 
enter  very  obliquely  under  the  mucosa,  somewhat  as  in  the  kidney,  so 
that  the  greater  the  pressure  within  the  viscus  the  less  likely  is  the  urine 
to  return  up  the  ureters.  The  smooth  muscular  fibers  of  the  bladder 
are  roughly  arranged  in  three  layers,  which,  however,  are  much  intermixed. 
A  thickened  portion  of  the  musculature  at  the  bladder's  outlet  constitutes 
the  sphincter,  which  is  usually  in  tonic  contraction.  Nerves  with  ganglia 
in  their  course  pass  both  to  the  mucosa  and  to  the  muscle-tissue.  The 
bladder  is  thus  supplied  with  sensory,  motor,  and  vasomotor  functions. 

Micturition,  the  voidance  of  urine  from  the  bladder,  consists  of  a  co- 
ordinated series  of  muscular  contractions  of  the  bladder,  the  abdomen, 
and  the  urethra.  In  children  up  to  about  the  eighth  month  the  process  is 
purely  reflex,  for  voluntary  inhibition  of  the  efferent  nervous  impulses  has 
not  then  been  acquired,  probably  because  of  the  undeveloped  state  of 
the  neurones.  In  adults,  on  the  other  hand,  voluntary  inhibition  may 
be  continued  until  the  bladder's  contractile  mechanism  has  become 
temporarily  paralyzed  by  the  pressure,  which  over-stretches  it.  The 
normal  retention  of  urine  is  the  result  of  a  functional  balance  between 
this  pressure  and  the  tonus  of  the  retaining  sphincter.  Gradually  the 
musculature  accommodates  itself  to  the  incoming  urine,  there  being  no 
cavity  in  the  bladder  immediately  after  micturition.  Nothing  is  felt 
of  this  increasing  pressure  until  300  or  400  cm.  of  urine  have  collected; 
then,  unless  the  attention  is  fixed  on  some  absorbing  pursuit,  the  person 
becomes  aware  of  a  desire  to  micturate,  especially  if  by  mechanical 
joggling  a  drop  of  urine  is  pushed  through  the  sphincter  into  the  very 
sensitive  beginning  of  the  urethra.     If  micturition  be  then  inconvenient. 


250 


NUTRITION 


Fig.  135 


2)X/// 


it  may  be  postponed,  but  by  irritation  of  the  nerves  in  its  walls  the  ever- 
tlistending  visciis  gradually  increases  the  sense  of  discomfort  until  it 
perhaps  becomes  actual  pain. 

The  forces  acting  in  micturition  are  the  contraction  of  the  bladder's 
muscular  walls,  the  passive  elasticity  of  the  viscus,  the  weight  and 
pressure  of  the  viscera  above  it,  and  the  weight  of  the  urine  in  the  bladder. 
The  first  two  of  these  tend  continually  to  lessen  the  size  of  the  organ 

much  as  is  the  case  with  the  stomach. 
These  four  forces  combined,  and  aided 
in  cases  of  haste  by  voluntary  con- 
traction of  the  rectus  abdominis,  etc.^ 
quickly  overcome  the  cohesion  of  the 
urethra's  walls  and  the  urine  passes 
out,  under  a  pressure  of  about  100 
mm.  of  mercury  or  more.  The  urine 
left  in  the  male  urethra  is  then  ex- 
pelled by  the  bulbocavernosus  and  the 
levator  ani  muscles. 

The  nerves  concerned  seem  to  come 
from  the  second,  third,  fourth,  and 
fifth  lumbar  vertebral  segments,  but 
the  sensory  (afferent)  and  the  in- 
hibitory (efferent)  impulses  pass  up 
and  down  the  cord's  lateral  columns 
to  the  cortex  cerebri,  while  some 
may  go  by  way  of  the  sympathetic. 
The  inhibitory  influence  relaxes  the 
sphincter.  The  mechanism  may  act 
quite  independently  of  the  central 
nervous  system,  directed  probably  by 
influences  from  local  ganglia  or  a 
nervous  reticulum.  Friedman  places 
a  supposed  micturition-center  in  the 
upper  third  of  the  posterior  central 
convolution  just  behind  the  center 
for  the  arm's  action.  The  bladder's 
contractions  are  rhythmic  in  nature, 
following  each  other  at  intervals 
averaging  about  fifty  seconds  (Sher- 
rington), in  a  way  somewhat  similar  to  the  contractions  of  the  uterus 
and  the  spleen.  The  difference  between  the  neural  mechanism  in  the 
adult  and  that  in  the  infant  may  very  well  be  largely  functional,  and 
consist  in  a  development  of  voluntary  control  over  the  smooth  muscle 
of  the  bladder.  This  is  seen  frequently  in  almost  all  the  smooth 
muscles  oi'  the  body,  and  is  not  very  rare  even  in  case  of  the  heart. 
The  bladder  is  one  of  the  most  sensitive  of  the  organs  to  nervous 
excitement  and  influences  of  many  sorts,  chemical  as  well  as  nervous. 


n.pr 


Tlie  innervation  of  the  kidney  and  of  the 
bladder:  K,  kidney;  B,  bladder;  i)xiii, 
thirteenth  dorsal  root  (dog);  pn.g,  vagus; 
n.sp,  splanchnics  (great  and  small);  gg.ms, 
superior  mesenteric  ganglion;  gg.hyp,  hypo- 
gastric ganglion  or  plexus;  n.er.,  erector 
ner\'e.      ("Morat.) 


METABOLISM  251 

Thus,  mental  agitation,  emotions,  and  also  slight  irritations  at  the  distal 
end  of  the  urethra  cause  frequently  a  desire  to  micturate. 

It  remains  to  suggest  the  ways  in  which  the  katabolie  waste  is  excreted 
through  the  lungs,  the  skin,  and  the  rectum. 

The  Expired  Air  excretes  waste  matter  next  in  importance  to  that  of  the 
urine,  this  matter  consisting  almost  wholly  of  carbon  dioxide  and  of 
water.  The  katabolism  which  produces  these  two  substances  has  been 
already  more  or  less  described  in  our  chapter  on  respiration  and  above 
in  this  chapter.  A  very  large  part  of  the  carbon  dioxide  and  about  one- 
sixth  of  the  water  passes  off  through  the  respiratory  organs.  The  sources 
of  the  water  we  have  already  seen  (page  240). 

The  carbon  dioxide  comes  from  the  oxidation  of  all  the  products  of 
katabolism  that  contain  carbon.  Some  of  that  arising  from  proteid 
passes  out  through  the  kidneys  in  the  form  of  urea.  ^Nfost  of  the  carbon 
dioxide  excreted,  therefore,  comes  from  the  carbohydrates  and  fats  of 
the  tissues  (and  the  blood?).  The  carbon  from  these  is  oxidized  to 
carbon  dioxide.  There  is  evidence  (obtained  by  Stoklasa)  that  the  tissue- 
cells  generally  produce  an  anaerobic  enzyme  which  occasions  the  fer- 
mentations of  sugar  to  carbon  dioxide  and  water;  it  is  foimd  also  in  milk 
and  in  blood.  This  evidence  Borrino  has  confirmed.  The  chief  seats 
of  this  oxidation  are  the  muscles;  then  come  the  glands  and  the  nervous 
system,  the  other  tissues  being  far  behind  these  as  sites  of  oxidation. 
The  muscles  furnish  about  three-quarters  of  all  the  carbon  dioxide 
excreted  by  these  means  combined. 

Suppositions  as  to  the  exact  mode  of  oxidation  have  been  various;  the 
real  way  or  ways  are  unknown.  Hoppe-Seyler  considered  it  possible 
that  nascent  hydrogen,  set  free  by  certain  decompositions,  caused  the 
diatomic  molecule  of  oxygen  to  split,  the  atoms  of  oxygen  thus  becoming 
very  active,  making  possible  a  vigorous  attack  on  substances  already  in 
process  of  katabolism.  Again,  Spitzer  supposes  iron  may  play  an 
important  part  in  causing  the  absorption  of  oxygen  into  the  breaking- 
down  cell-protoplasm.  This  always  contains  iron  in  the  nucleus,  and 
ferrous  iron  may  act  as  a  carrier  between  the  oxygen  and  the  molecule, 
alternately  taking  on  and  losing  an  atom  of  oxygen  (Herter).  Probably 
(Traube)  there  are  enzymes  which  cause  the  primary  katabolism  of  the 
fats  and  the  carbohydrates,  or  even  the  absorption  of  oxygen  into  the 
products  of  this  katabolism.  The  pancreas  may  furnish  such  an  enzyme 
to  sugar — a  ferment  called  an  oxidase.  Again,  as  Herter  suggests,  the 
hydroxyl  (HO)  ions  of  the  alkaline  salines  of  protoplasm  may  be  the 
ultimate  cause  of  oxidation,  perhaps  by  dissolving  the  katabolie  carbon 
dioxide  and  so  removing  it  from  the  tissues,  perhaps  by  liberating  nascent 
oxygen  to  attack  the  tissue-molecules,  water  being  simultaneously 
formed. 

Regardless  of  hypotheses,  it  is  certain  that  oxidation  is  inherent  in 
protoplasm  and  that  without  it  life  cannot  continue.  The  nucleus  in 
case  of  the  tissues  is  apparently  the  agent  or  at  least  the  director  of  the 
process.     There  is  no  reason  why  there  should  be  only  one  way  in  which 


252  NUTRITION 

the  many  various  substances  of  the  food  and  tissues  are  oxidized,  so 
general  is  the  process  and  chemism  so  various. 

The  fats  and  the  carbohydrates  from  which  water  and  carbon  dioxide 
(by  oxidation  of  their  carbon)  largely  come  have  already  been  sufficiently 
described,  as  have  also  the  means  by  which  these  excreta  are  transported 
from  the  tissues  and  given  out  by  the  lungs  and  nasal  passages  through 
the  nostrils.  (See  the  descriptions  of  katabolism  above  and  the  dis- 
cussion of  respiration  in  a  preceding  chapter.) 

The  Sweat  is  the  next  most  important  of  the  means  of  excreting  some 
of  the  waste-products  of  katabolism.  These  are  especially  water,  urea, 
ammonia,  kreatinin,  sodium  chloride,  and  phosphate,  the  inorganic  and 
ethereal  sulphates,  fats  (Reid),  and  the  inorganic  salts,  largely  sodium 
chloride.  The  amount  of  water  excreted  through  the  skin  it  is  hard 
to  estimate  from  the  discordant  results  obtained  by  experiment,  for  it 
greatly  varies  not  only  at  different  times  and  under  different  internal 
and  external  conditions,  but  also  on  different  parts  of  the  skin.  The 
"insensible"  sweat  is  the  more  important  in  studying  normal  excretion, 
yet  every  known  means  of  measurement  at  once  increases  its  output 
many  times.  On  the  whole  the  average  daily  quantity  is  probably  not 
far  from  1500  grams,  the  same  as  that  of  the  urine,  as  will  be  recalled. 
So  far,  then,  as  excreting  water  is  concerned,  these  two  means  are  equiva- 
lent and  the  balance  of  their  well-known  and  important  reciprocal  action 
(one  decreasing  in  amount  as  the  other  increases)  is  rendered  more 
perfect. 

The  Feces,  although  consisting  daily  of  several  hundred  grams  of  waste 
material,  excrete  but  a  very  small  proportion  of  strictly  katabolic  product, 
for  they  are  in  large  part  merely  the  refuse  of  the  digestive  apparatus. 
It  is  here,  however,  that  the  systematic  description  of  the  feces  properly 
belongs. 

The  quantity  of  the  feces  defecated  daily  by  an  adult  living  on  an 
ordinary  mixed  diet  is  about  160  grams,  but  on  a  vegetal  diet  the  amount 
may  be  three  times  as  great,  the  difference  being  largely  due,  directly 
or  indirectly,  to  cellulose.  The  percentage  of  water  is  from  60  to  more 
than  80;  the  latter  proportion  belongs  to  the  feces  from  a  vegetal  diet, 
because  peristalsis  is  then  much  more  active  and  less  time  is  allowed 
for  the  water's  absorption  into  the  lymph-  or  blood-vessels  of  the  colon. 
The  fecal  color  varies  from  light  yellow  to  black,  depending  on  the 
amount  of  bile-pigments  (stercobilin),  iron  salts,  and  sulphuretted' 
hydrogen  present.  The  odor  is  due  largely  to  skatol,  but  sulphuretted 
hydrogen,  fatty  acids,  and  indol  take  part.  The  chemical  reaction  of 
feces  may  be  either  acid  or  alkaline. 

The  composition  of  the  feces  is  of  course  exceedingly  variable,  for  it 
depends  directly  on  the  food  ingested  and  not  absorbed.  Water  makes 
about  three-quarters  of  its  weight,  and  much  of  the  solid  material  is 
undigested  and  indigestible  bits  of  food  and  dried  (Hg(\stive  juices.  The 
undigested  part  of  the  food  consists  of  bits  of  meat,  fat-globules,  and 
carbohydrate;  the  indigestible  fragments  are  of  l)one,  ligaments,  keratin. 


METABOLISM  253 

cellulose,  and  vegetal  gums.  Then  there  are  residues  from  the  bile: 
stercobilin  (similar  to  or  identical  with  urobilin  and  hydrobilirubin), 
the  product  of  the  unabsorbed  bile-pigments,  and  bile-salts  likewise 
for  some  reason  unabsorbed  from  the  colon.  Cholesterin  is  always 
present,  as  the  refuse  of  the  hepatic  metabolism,  as  well  as  lecithin.  The 
antiseptic  mucin  from  the  goblet-cells  of  the  colon  and  detritus  from 
the  whole  length  of  the  alimentary  canal's  mucosa  are  never  absent. 
Bacterial  putrefaction,  active  despite  the  antiseptic  powers  of  the  colon's 
mucus,  contributes  the  tyrosin  and  its  derivatives  (skatol,  etc.)  already 
noted,  besides  various  complex  organic  and  fatty  acids  and  insoluble 
soaps.  Then  there  is  a  substance  unfortunately  named  secretin  whose 
empirical  formula  is  said  to  be  CjoHggO,  and  which  has  not  been  found 
outside  of  human  feces.  (This  has  nothing  to  do  with  the  secretin 
internally  secreted  by  the  duodenal  wall.)  There  are  also  many  soluble 
and  insoluble  salts  of  the  chief  organic  metals,  calcium,  sodium,  potas- 
sium, magnesium,  and  iron. 

Of  the  above  fecal  components,  water,  stercobilin,  the  bile-salts, 
cholesterin,  lecithin,  mucin,  and  most  likely  secretin  represent  in  one  way 
and  place  or  other  the  katabolism  of  the  tissues,  but  largely  in  a  manner 
chemistry  cannot  at  present  explain  in  detail.  Of  the  total  three  liters  or 
so  of  water  daily  excreted,  about  150  c.c.  (or  more  on  vegetal  diet)  pass 
out  in  the  feces;  this  is  about  5  per  cent.  Stercobilin,  the  name  of  the 
reduced  bilirubin  of  the  rectum,  represents  the  iron  and  the  proteid 
katabolism  in  the  liver,  as  do,  and  more  especially,  the  bile-salts.  These 
latter  contain  nitrogen  and  some  of  them  also  sulphur,  but  no  iron. 
Both  of  these  hepatic  products  (pigments  and  salts)  probably  have,  to 
some  extent  at  least,  a  "circulation,"  being  absorbed  from  the  colon 
into  the  blood,  the  pigment  being  then  made  over  into  the  hematin  of 
new  erythrocytes  and  the  bile-acids  entering  into  anabolic  process  even 
less  understood,  thus  saving  much  constructive  energy  and  material. 
The  cholesterin  and  lecithin  are  apparently  universal  katabolic  waste 
from  protoplasm.  The  mucin,  as  is  well-known,  consists  of  the  actual 
bodies  of  broken-down  epithelium,  and  represents,  therefore,  as  found  in 
the  feces,  but  a  minimum  of  katabolic  change. 


CHAPTER  VII. 

THE  BLOOD  AND  THE  LYMPH. 

We  have  discussed  already  the  ways  in  which  the  various  nutrients 
(inckiding  oxygen)  become  incorporated  in  the  organism  to  furnish  it 
energv  and  the  materials  for  replacing  its  ever- wasting  tissues.  The 
means  by  which  the  oxygen  and  the  absorbed  food  products  are  dis- 
trihuted  to  the  myriad  tissue-cells,  some  very  remote,  and  by  which  the 
waste  of  these  cells  is  removed,  remain  to  be  described.  These  means 
are,  of  course,  the  blood  and  lymph.  Combined,  these  constitute  one  of 
the  most  essential  of  bodily  tissues.  Blood  requires  two  modes  of 
description,  one  of  its  chemical  composition  and  the  other  of  its  morpho- 
logical structin-e. 

Physically  human  blood  consists  of  a  liquid  bearing  withm  it  two  sorts 
of  corpuscles  and  little  masses  known  as  platelets  not  properly  classed 
as  corpuscles.  The  liquid  is  called  plasma  and  the  three  kinds  of  bodies 
are  the  erythrocytes,  or  red  corpuscles,  the  leukocytes,  or  white  corpuscles, 
and  the  thrombocytes,  or  platelets.  In  chemical  composition  blood  is 
exceedingly  complex,  theoretically  more  so  even  than  the  varied  tissues, 
for  it  contains  not  only  the  materials  on  which  the  tissues  live,  but  also  the 
multifarious  end-products  of  tissue-katabolism.  Lymph  is  so  nearly 
like  blood-plasma  in  its  composition  that  they  are  properly  studied 
together. 

The  Chemical  Composition  of  the  Blood  and  Lymph  has  been  more  or  less 
described,  indirectly,  in  the  preceding  chapters,  but  rec^uires  to  be  set 
forth  systematically.  We  shall  then  all  the  better  appreciate  in  how 
literal  a  sense  the  circulation  is  but  a  means  of  distributing  the  food, 
oxygen,  and  heat,  and  of  collecting  the  waste,  of  the  body.  Because  these 
two  processes  comprise  one  of  the  largest  functions  of  life,  nutrition,  a 
good  knowlerlge  of  the  blood  is  of  unexcelled  importance,  for  this  com- 
plex "licjuid"  is  indeed  "life-blood."  When  it  stops  moving  in  its  devious 
way  among  the  cells  life  departs  and  death  more  or  less  gradually  comes 
on.  Mammalian  blood,  as  we  have  seen,  consists  of  plasma  containing 
erythrocytes,  leukocytes,  and  thrombocytes.  Each  of  these,  as  well  as 
lymph  and  serum,  has  functions  and  in  consequence  a  chemical  composi- 
tion i)eculiar  to  itself  which  must  })e  outlined  each  in  its  turn.  The 
functions  and  the  physical  composition  of  the  whole  blood  will  be  then 
the  better  understood. 

The  following  sul^stances  appear  to  be  regular  constituents  of  human 
Idood  in  its  normal  circulating  condition.  There  are  doubtless  many 
others  in  mere  traces  and  perhaps  still  others  of  importance  not  yet 


THE  BLOOD  AND  THE  LYMPH  255 

isolated.  Water  (80  per  cent.),  serum  all)iimin,  paraglobulin,  nucleo- 
proteid,  fibrinogen,  jecorin,  hemoglobin,  thrombin,  dextrose,  glycogen, 
fats,  lecithin,  serum  lutein,  oxygen,  nitrogen,  sodium  chloride,  sodium 
carbonate,  stxlium  phosphate,  potassium  chloride,  potassium  phosphate, 
potassium  sulphate,  calcium  phosphate,  magnesium  phosphate,  various 
enzymes;  lactic  acid,  kreatin,  kreatinin,  urea  (trace  only),  uric  acid, 
xanthin,  cholesterin,  and  carbon  dioxide.  This  list  of  substances,  repre- 
senting potentially  all  that  goes  on  chemically  in  the  body  one  way  or 
another,  will  be  found  useful  for  future  reference.  Those  to  be  used  in 
the  body  are  given  first.  The  last  eight  are  products  more  or  less  of 
katabolism,  and  are  therefore  mostly  outward  bound  from  the  system. 
The  chemical  components  of  the  plasma  and  lymph  may  be  de- 
scribed together,  for  these  two  are  practically  alike  save  that  the  lymph 
contains  leukocytes  and  more  water  than  the  plasma.  Plasma  is  whole 
blood  as  it  circulates  in  the  arteries  and  veins  minus  the  three  sorts  of 
corpuscles.  Lymph  is  found  almost  everywhere  outside  of  the  tubes 
of  the  circulation,  and  everywhere,  too,  within  the  closed  system  of  the 
lymphatics,  which  are  almost  imiversal  in  the  body.  In  the  portal 
veins  (bearing  the  products  of  absorption  from  the  gut)  just  after  a  meal 
this  lymph  is  white,  being  an  emulsion,  especially  if  the  latter  contain 
much  fat.  It  is  there  and  then  called  chyle,  as  is  also  the  contents  of  the 
small  intestine. 

Hammarsten  found  the  'plasma  of  horse's  blood  to  have  the  following 
composition : 

Plasma's  Chemical  Composition. 

Water 917.6 

Fibrin  (from  fibrinogen) 6.5 

Paraglobulin 38.4 

Serum  albumin 24 . 6 

Salts,  fats,  dextrose,  kreatinin,  etc.  ("extractives")     .  12.9 

1000.0 

Human  plasma  has  a  somewhat  smaller  proportion  of  paraglobulin 
and  a  larger  proportion  of  serum-albumin.  "When  an  animal  fasts  the 
former  increases  and  the  latter  decreases.  The  fats  are  tristearin, 
tripalmitin,  and  triolein,  while  the  carbohydrates  are  dextrose  and 
glycogen  and  perhaps  animal-gum.  The  salts  are  the  chloride,  carbon- 
ate, sulphate,  and  pho.sphate  of  sodium,  etc.,  as  given  in  the  list  above. 
The  katabolic  nitrogenous  substances  are  especially  urea  (0.016  per 
cent.),  kreatin,  lactic  acid  (possibly  carbonic  acid  and  sarcolacdc  acid). 
Carbon  dioxide  is  present  dissolved  in  the  plasma  as  well  as  in  the  sodium 
carbonate  and  leukocytes. 

In  some  lymph,  perhaps  rather  thinner  than  the  average,  taken 
from  a  fistula  in  a  man's  leg,  Hensen  and  Diihnhardt  found  the  following 
proportions,  nearly: 


256  THE  BLOOD  AXD  THE  LYMPH 

Chemical  Compositiox  of  Lymph. 

Water 986.3 

Fibrin 11 

Albiunin 1.4 

Alkali-albuminate 0.9 

Urea  and  leucin .      .■  1.0 

Other  extractives 0.5 

Salts 8.8 

1000.0 

A  mixture  of  Ivmph  and  of  chyle  taken  from  the  thoracic  duct  Rees  found 
to  contain  9.5  per  cent,  of  sohds,  of  which  7.8  per  cent,  were  proteids  and 
1  per  cent,  each  extractives  and  fatty  materials.  This  might  be  termed 
digestion-lymph.  Note  that  as  compared  with  plasma,  tissue-lymph 
contains  much  more  water,  much  less  fibrin,  and  less  salts,  fats,  and 
sugars.  The  Ivmph  is  also  much  more  variable  than  is  plasma,  since  it 
depends  more  or  less  for  its  compo.sition  on  the  metabolism  of  the  tissue 
where  it  is  found.  A  sample  of  pericardial  fluid  (lymph j  was  found  to 
be  richer  in  solids,  while  cerebro-spinal  fluid  (lymph)  Hoppe-Seyler 
found  very  little  different  from  that  reported  above  from  the  man's  leg. 
Chyle  is  richer  in  fats  and  in  proteids  than  lymph,  but  it  is  otherwise 
similar.  Synovia  (of  the  joints)  contains  much  the  same  solids  as  lymph 
but  more  of  them,  and  in  addition  a  mucin-like  substance  (Salkowski). 

The  chemical  components  of  the  erythrocytes  or  red  corpuscles. 
These  little  bodies  consist  largely  of  water,  hemoglobin,  nucleo-proteid, 
lecithin,  cholesterin,  and  salts  of  potassium  and  of  phosphoric  acid. 
The  .solids  are  one-third,  or  a  Httle  more,  of  the  whole  mass  of  moist 
corpuscles.  The  proteid  stroma  of  the  red  corpuscles  appears  to  be  a 
globulin.  It  is  noteworthy  that  while  sodium  salts  much  exceed  in 
amount  the  potassium  salts  in  the  plasma,  in  the  erythrocytes  the  rever.se 
is  true. 

Hemoglobin  is  a  variable  histone-like  globulin  called  globin  combined 
with  about  4  per  cent,  of  a  non-albuminous,  iron-containing  pigment 
of  constant  composidon  called  hematin.  It  is  theoretically  interesting 
that  hemoglobin  is  probaVjly  nearly  or  quite  identical  with  the  pigment 
of  chlorophyll  or  plant-green  so  nearly  universal  in  the  vegetaljle  kingdom. 
It  is  by  means  of  this  .substance  that  the  plant  breathes  and  in  the  sun- 
light i.s^  able  to  construct  carbohydrates  out  of  purely  inorganic  materials, 
and  through  the  agency  of  the  hemoglobin  in  animals  their  tissues  are 
.supplied  with  the  metabolic  and  life-giving  oxygen.  When  combined 
with  the  latter  gas,  hemoglobin  is  called  oxy-hemoglobin,  and  when  this 
oxygen  has  been  removed  it  is  called  reduced  hemoglobin.  The  empir- 
ical formula  of  the  hemoglobin  of  the  dog  is  about  Cjr^gHijsaNjgaSgFeOaig, 
while  Gamgee  calculates  that  the  hemoglobin  of  the  ox  has  the 
formula  Cr,^^i2<>H^2x<f^^^^'^2W  ^''^'"K  a  molecular  weight  of  16,669. 
Although  crystalline,  oxy-hemoglobin  is  quite  indiflusible,  perhaps 
becau.se  of  this  large  size  of  its  molecule.     It  may  be  this  quality  which 


THE  BLOOD  AND  THE  LYMPH  257 

prevents  its  osmosis  out  of  the  capillaricvs  into  the  tissue-spaces.  As 
Bunge  suggests,  this  large  molecule  with  its  relatively  great  momentum 
would  more  easily  transport  the  very  heavy  atoms  of  iron  than  would  a 
small  molecule.  Its  great  size  and  complexity  helps  undoubtedly  in  its 
instability,  and  this  is  a  very  important  quality  for  the  performance  of 
its  functions.  Dry  hemoglobin  contains  nearly  0.5  per  cent,  of  its 
weight  of  iron,  and  it  is  doubtless  on  this  metal  that  its  quick  alternate 
oxidation  and  reduction  depend.  Oxy-hemoglobin  is,  then,  the  form 
of  the  substance  present  in  the  arterial  blood  antl  reduced  hemoglobin 
that  of  venous  blood.  It  is  of  practical  importance  that  hemoglobin 
readily  forms  more  or  less  stable  unions  with  gases  other  than  oxygen, 
notably  carbon  dioxide,  nitric  oxide,  and  the  fatal  carbon  monoxide. 
Because  of  the  chemical  affinity  for  the  last  of  these  three,  coal  gas  and 
impure  water  gas  cause  many  deaths  annually,  the  carbon  monoxide 
replacing  and  excluding  the  respiratory  oxygen  from  the  erythrocytes. 

Since  the  development  of  hematology  in  the  progressive  division  of 
medical  labor,  discussion  of  the  various  spectra  of  the  blood,  comparison 
of  solutions  of  hemoglobin,  etc.,  have  become  less  and  less  a  part  of  the 
science  of  physiology  proper.  Suffice  it  here  to  say,  then,  that  each  of 
the  different  compounds  and  pigment-derivatives  of  hemoglobin  has  an 
absorption-spectrum  peculiar  to  itself,  and  that  by  this  means  blood 
may  be  readily  recognized  even  in  very  old  stains.  Much  may  be  learned 
from  the  blood  by  this  method  and  others  as  to  certain  pathological 
conditions. 

The  chemical  components  of  the  leukocytes,  or  white  corpuscles, 
has  so  far  not  been  directly  determined,  except  that  of  pus-cells.  These 
are  dead  protoplasm,  however,  whereas  the  leukocytes  are  alive,  and  there 
is  as  much  diiference  chemically  doubtless  as  otherwise.  Halliburton 
quotes  an  analysis  of  lymphoid  tissue  made  by  Wooldridge  which  the 
former  considers  similar  to  that  of  leukocytes.     This  is  as  follows: 

Probable  Composition  of  Leukocytes. 

Water 885.1 

Solids 114.9 

ICOO.O 

Nuclein 68.78% 

Proteid 1.76 

Histon 8.67 

Lecithin 7.51 

Fat 4.02 

Cho'esterin 4.40 

Glycogen 0.80 

Total  nitrogen 150.3 

Total  phosphorus 30.1 

Among  the  proteids  are  alkali-albumin,  a  myosin-like  albumin,  para- 
globulin,  and  peptone.     There  is,  moreover,  probably  "thrombin"  in 
small  amount. 
17 


258  THE  BLOOD  AND  THE  LYMPH 

The  chemical  components  of  the  thrombocytes,  or  platelets, 
because  of  the  smallness  and  fewness  of  these  floating  particles,  is  not 
definitely  known.  They  consist  perhaps  chiefly  of  nucleo-proteid,  or  of 
globulin.  Biirker  has  recently  shown  l)y  quantitative  and  gravimetric 
methods  that,  whatever  their  composition,  the  fibrin  of  coagulation 
probably  comes  from  them  (see  discussion  of  coagulation  on  page  2(30). 

Whole  blood,  or,  more  simply,  blood,  is  a  "tissue"  of  the  body  in 
which  the  morphological  "matrix"  is  a  liquid  with  important  functions, 
the  contained  cells  being  the  three  sorts  already  noted.  It  constitutes 
about  7  per  cent,  by  weight  of  the  human  body.  Its  specific  gravity 
is  from  1050  to  1062,  that  of  women  and  children  ranging  from  the  lower 
number  to  1055,  and  man's  from  1057  to  1062.  The  specific  gravity  of 
the  corpuscles  is  about  1105,  and  of  the  plasma  not  far  from  1030.  In 
chemical  reaction  blood  is  always  alkaline  because  of  its  plasma's  sodium 
phosphate  and  carbonate.  The  mean  alkalinity  of  the  blood  is  about 
equal  to  that  of  0.4  per  cent,  solution  of  sodium  hydrate.  It  is  lowest 
in  the  morning  and  highest  at  night.  Owing  to  the  passage  into  the 
circulation  of  lactic  acid  (from  the  decomposition  of  the  muscle's  proteid), 
bodily  exercise  decreases  the  blood's  alkalinity.  In  color  blood  varies 
from  the  dull  scarlet  of  the  pulmonary  vein,  leading  from  the  air  in  the 
lungs,  to  the  purplish  red  of  the  pulmonary  artery,  leading  from  the 
oxygen -reducing  tissues.  The  tinge  then  depends  on  the  proportion  of 
oxygen  in  the  erythrocytes.  The  color-difference  in  health  is  much  less 
than  is  generally  supposed  by  those  who  use  anatomical  text- books  with 
colored  plates.  It  is  in  mass  only  that  blood  is  red.  No  redness  is  per- 
ceptiljle  in  the  capillaries,  and  the  file  of  erythrocytes  there  is  of  a  light 
straw-yellow  color;  yet  it  is  from  masses  of  these  corpuscles  that  the 
redness  of  blood  comes.  In  taste  blood  is  saline,  this  being  due  largely 
to  the  sodium  chloride  of  the  plasma.  The  odor  of  })lood  is  character- 
istic, and  is  largely  caused  by  the  various  volatile  fatty  acids  and  the 
traces  of  excretory  products  present.  The  viscidity  of  blood  is  due  to  its 
composition  and,  soon  after  shedding,  to  commencing  coagulation. 
Blood  is  markedly  opaque,  as  is  inevitable  in  a  colored  liquid  containing 
so  many  opaque  bodies  in  suspension.  The  temperature  of  the  circulating 
blood  varies  more  than  a  degree  in  different  bodily  parts.  It  is  highest 
where  the  blood  is  coming  from  the  actively  metabolic  liver,  the  largest 
single  heat-producer  in  the  organism.  The  blood  constitutes  one-twelfth 
or  one-thirteenth  of  a  man's  body  weight,  a  man  of  average  size  having 
then  about  five  liters  of  blood  in  his  body.  The  loss  of  one  of  these 
liters  would  ordinarily  kill  him,  but  a  woman  might  lose  proportionally 
somewhat  more  and  survive.  The  blood's  distribution  in  general  is 
about  as  follows  (Ranke) :  One-fourth  of  it  is  in  the  circulation  including 
the  lungs,  another  fourth  in  the  skeletal  muscles,  another  in  the  liver, 
and  the  remaining  (|uarter  is  aj^portioued  among  the  other  parts  of  the 
body.  During  inanition  the  lilood  sometimes  becomes  more  concen- 
trated, the  proportion  of  erythrocytes   somewhat  greater,  the  number 


THE  BLOOD  AND  THE  LYMPH  259 

of  leukocytes  decreased  bv  90  per  cent.,  Init  the  alkalinity  is  not  lessened, 
and  the  sugar-content  remains  the  same. 

Few  aspects  of  the  chemical  composition  of  the  blood  are  more  im- 
portant than  that  of  its  electrolytic  conductivity  by  means  of  ions,  for 
on  the  relative  number  of  its  molecules  and  its  ions  depends  probably 
much  of  the  osmotic  force  everywhere  exerted  by  the  blood  and  lymph. 
On  everv  hand  we  have  seen  the  importance  of  osmosis  and  diffusion 
in  bodily  functions,  and  few  of  the  physiological  processes  are  inde- 
pendent of  these  physical  processes.  It  has  been  found  that  so  far  as 
determining  osmotic  pressure  is  concerned,  an  ion  acts  exactly  like  a 
complete  molecule.  Hence  the  relative  degree  of  dissociation  into  ions 
which  the  body-licjuids  exhibit  under  various  conditions  determines  very 
largely  most  of  the  functions  of  the  organism.  According  to  the  recently 
sufffifested  electrical  theorv  of  organic  functioning,  the  more  dilute  an 
electrolyte,  for  example  the  blood,  is,  the  more  ions  does  it  contain  and 
the  better  it  conducts  the  supposed  compUcated  electric  currents  of  the 
bodv's  action.  Because  of  their  membranous  nature,  the  blood-cor- 
puscles impede  the  passage  of  the  ions  which  bear  the  electricity,  while 
the  plasma  is  an  excellent  electrical  conductor.  The  fewer  the  corpuscles 
in  blood  proportional  to  the  plasma,  then,  the  better  the  blood's  conduc- 
tivity. Again,  the  more  ions  or  molecules  a  solution  contains  the  greater 
IS  its  osmotic  pressure  through  the  animal-membranes  (the  capillary 
walls,  cell-walls,  Bowman's  capsule,  etc.)  of  the  organism.  The  cor- 
puscles of  the  blood  are  in  this  category,  so  that  interchanges  are  con- 
tinually taking  place  between  them  and  the  plasma  as  the  degree  of  dis- 
sociation of  their  ions  and  the  concentration  of  the  electrolytes  determine. 
It  is  not  only  the  "inorganic"  salts  of  the  blood  that  furnish  the  ions,  but 
the  colloidal  proteids  and  "extractives"  as  well.  Because,  however, 
of  the  large  molecules  of  the  proteids  and  of  some  of  the  extractives,  the 
osmotic  pressure  exerted  by  these  substances  is  small  compared  with 
that  of  the  "inorganic"  salts.  On  the  other  hand,  the  saline  solutions 
osmose  very  readily  and  quickly  and  by  this  action  largely  control  the 
passage  of  the  blood's  nutrients  and  of  the  tissue-waste  in  and  out  of  the 
circulation  and  the  tissues.  It  is  on  these  principles  (here  only  rudely 
outlined)  that  the  composition  of  the  blood  in  these  ionic  respects  is  of 
the  largest  importance.  This  composition  has  control  not  only  over 
metabolism  by  chemical  means,  but  also  in  other  ways  which  chemo- 
physics  will  doubtless  soon  make  more  clear. 

Whole  Blood's  Compositiox  (Schmidt). 

Water 788.71 

Proteids  and  extractives 191.78 

Fibrin  (from  fibrinogen) 3 .  93 

Hematin  (and  iron) ■.      .  7.70 

Salts 7.88 


1000.00 


260  THE  BLOOD  AND  THE  LYMPH 

The  above  analysis  of  the  blood  of  a  man  shows  the  relative  general 
amounts  of  the  blood's  components.  In  woman  the  salts  and  the  water 
are  in  somewhat  larger  proportion.  Under  the  head  of  proteids  were 
included  serum-albumin,  paraglobuHn,  nucleo-proteid,  jeeorin,  and 
thrombin,  while  the  "extractives"  were  such  various  substances  as 
dextrose,  glycogen,  fats,  lecithin,  lutein,  lactic  acid,  kreatin,  kreatinin, 
urea,  uric  acid,  xanthin,  and  cholest&rin.  The  salts  may  be  noted  from 
the  preliminary  complete  list  of  the  blood's  constituents  on  page  255. 
They  are  chiefly  chlorides,  phosphates,  carbonates,  and  sulphates  of 
the  common  tissue-metals. 

Coagulation  of  the  blood  is  a  function  essential  to  the  continuance 
of  life,  for  without  it  any  wound,  however  small,  in  the  tissues  would 
cause  death  by  hemorrhage.  This  fact  is  all  too  often  illustrated  in 
the  victims  of  hemophilia,  commonly  called  "bleeders."  Something- 
is  lacking  congenitally  in  their  blood  so  that  it  does  not  coagulate.  In 
consecjuence  of  this  defect  they  almost  always  die  before  maturity  by 
hemorrhage  from  an  open  tooth-socket,  the  nose,  or  from  some  minor 
wound  of  the  skin. 

Given  a  multitude  of  soft  corpuscles  floating  in  a  thin  liquid:  the 
evolutionary  problem  was  to  contrive  a  way  of  uniting  them  quickly 
into  a  solid  mass  dense  enough  to  obstruct  the  blood-stream  flowing 
swiftly  and  under  considerable  pressure  through  an  injured  vessel.  For 
this  purpose  nothing  could  be  better  than  a  mesh  of  fine  but  tough  and 
elastic  fibers  quickly  formed  in  the  blood  when  suddenly  needed  but  by 
no  means  until  then  nor  in  any  other  place  than  at  the  seat  of  injury. 
Such  indeed  is  the  fibrin  which  forms  in  extra  vasated  blood  or  in  the  blood- 
vessels whose  walls  have  been  badly  injured,  and  thus  made  dangerous 
to  the  organism.  How  is  this  fibrin  net-work  formed  and  from  which 
of  the  blood's  components  ?     It  is  not  quite  certain  as  yet. 

As  the  name  of  the  thrombocytes  (given  by  Dekhuysen  to  the  platelets) 
implies,  it  is  perhaps  this  third  sort  of  blood-particles  which  have  most 
to  do  with  coagulation.  In  1904  Biirker  studied  them  in  great  detail. 
He  found  that  when  a  drop  of  blood  was  placed  on  a  polished  bit  of  clean 
paraffin  in  a  moist-chamber,  in  half-an-hour  or  less  the  thrombocytes 
rose  to  the  top  of  the  drop,  being  lighter  than  the  plasma,  and  with  no 
dependence  on  the  leukocytes.  Under  these  excellent  microscopic 
conditions  the  coagulation  of  the  drop  of  blood  could  be  accurately 
studied.  It  was  seen  that  the  coagulation-time  depended  directly  on 
the  relative  number  of  thrombocytes  present  in  the  drop,  and  that  those 
substances  which  inhibit  coagulation  (for  example  leech-extract)  do 
so  by  preventing  the  decomposition  of  the  thrombocytes.  On  the 
other  hand,  those  agencies  which  hastened  coagulation  killed  the  platelets. 
Just  before  clotting  was  apparent  in  the  blood  (of  man,  cats,  dogs, 
hens,  frogs,  etc.,  at  least),  the  thrombocytes  were  observed  by  Ducceschi 
to  agglutinate  in  white  masses  a  quarter  or  a  half  of  a  millimeter  in 
diameter  on  the  sides  of  the  containing  vessel,  and  this  occurred  from 
forty  to  one-hundred-and-twenty  seconds  before  any  fibrin  had  formed. 


THE  BLOOD  AND  THE  LYMPH  261 

Soon  after,  threads  of  fibrin  shot  outward  from  all  these  little  masses 
and  soon  the  contained  erythrocytes  and  leukocytes  were  firmly  en- 
meshed in  this  net,  made  of  the  finest  of  fine  threads.  These  immediately 
began  to  contract  upon  the  corpuscles,  so  making  firmer  the  clot.  Of 
this  latter,  however,  not  more  than  0.2  per  cent,  is  fibrin.  Cray-fish 
blood  contains  particles  which  are  like  large  thrombocytes  and  on  the 
blood's  shedding  these  break  up  with  extreme  quickness,  with  the  result 
that  cray-fish  blood  coagulates  much  more  promptly  than  that  of  most 
animals. 

In  human  blood  coagulation  begins  as  an  increasing  viscosity  immedi- 
ately and  by  the  end  of  from  three  to  ten  minutes  (depending  on  external 
conditions  partly),  the  blood  has  formed  into  a  jelly  from  which  on  over- 
turning no  lic{uid  escapes.  This  mass,  the  dot,  is  gradually  concentrated 
by  the  contraction  of  the  fibrin,  and  lessening  in  size  for  a  day  or  two 
leaves  around  it  a  yellowish  limpid  liquid  called  serum.  Various  agents 
vary  the  rapidity  of  coagulation.  The  more  foreign  matter  there  is 
scattered  through  and  around  the  blood  and  the  more  the  latter  is  agitated 
the  quicker  it  clots.  A  few  degrees  of  heat  above  the  body-temperature, 
and  injury  to  the  endothelium  of  the  containing  blood-vessels  act  in 
a  similar  direction.  So  does  the  addition  of  calcium  salts  (for  example, 
the  lactate),  to  the  circulation  of  the  animal  previously,  or  of  the  xanthins, 
uric  acid,  etc.,  to  the  shed  blood.  Acids  and  alkalies,  glycerin,  oxalates, 
magnesium  sulphate,  peptone,  egg-albumin,  and  considerable  cold  are 
some  of  the  agents  which  inhibit  coagulation.  It  has  long  been  a  mystery 
why  the  blood  fails  to  coagulate  in  the  uninjured  blood-vessels,  even 
when  they  are  excised  and  hung  up,  but  it  is  now  likely  that  the  normal 
endothelium  secretes  some  enzyme  or  other  form  of  substance  which 
prevents  the  clotting.  ^Mien  blood  does  clot  in  the  vessels  the  process 
begins  in  the  center  and  not  about  the  walls  where  the  inhibiting  influence 
would  be  the  stronger.  Biirker  found  that  the  coagulation-time  was 
constant  for  each  individual.  He  also  learned  that  the  shortest  time  is 
late  in  the  afternoon,  and  that  independently  of  the  outside  temperature 
at  the  hour.  Although  cold  is  in  our  list  of  inhibiting  influences,  it  is 
often  used  in  medicine  to  check  hemorrhage  because  sometimes,  as  in 
the  vagina,  its  contracting-power  over  the  bleeding  blood-vessels  more 
than  counteracts  its  influence  over  the  coagulating  process.  In  hemo- 
philia thyroid  extract  is  said  to  be  effective,  but  in  what  way  is  unknown; 
adrenalin  acts  by  vaso-constriction. 

The  chemistry  of  blood-coagulation  has  not  been  as  yet  made  out  with 
certainty,  but  many  things  imply  that  the  general  reactions  are  somewhat 
as  follows:  Under  the  negative  influence  of  the  removal  of  the  inhibiting 
substance  secreted  by  the  endothelium,  or  under  the  stimulus  of  some 
sort  coming  from  contact  with  foreign  bodies,  or  both,  the  thrombocytes 
of  the  shed  blood  (or  leukocyte-  or  erythrocyte-nuclei)  exude  a  nucleo- 
proteid  which  unites  with  the  calcium  salts  of  the  plasma  to  form  a 
coagulating  ferment  called  thrombin.  This  enzyme  acts  on  the  fibrinogen 
(perhaps  a  globulin)  of  the  plasma  and  converts  it  into  two  substances. 


262  THE  BLOOD  AXD  THE  LYMPH 

One  of  these  is  the  insoluble  fibrin,  while  the  other  is  a  globulin  called 
fibrin-globulin.  This  latter  is  a  mere  by-product,  so  far  as  known, 
of  this  reaction,  whose  sole  purpose  is  to  construct  the  fibrin-mesh. 
This  is  substantially  the  doctrine  developed  especially  by  Schmidt,  Pekal- 
haring,  and  Hammarsten.  ]\Iore  lately  evidences  of  a  precursor  of  the 
thrombin  have  been  discovered  which  is  perhaps  also  an  enzyme.  Thus 
^lorawitz  supposes  that  a  substance  called  prothrombin  or  thrombogen 
(occurring  only  in  blood  and  lymph)  under  the  influence  of  thrombo- 
kinase  (an  enzyme  occurring  in  all  tissues),  unites  with  the  calcium  salts 
to  form  the  ferment  thrombin  (this  "thrombogen"  being  the  nucleo- 
proteid  spoken  of  above).  Besides  the  thrombocytes,  the  leukocytes 
may  take  part  in  the  reaction  by  furnishing  part  of  the  nucleo-proteid. 
It  is  very  doubtful,  however,  if  this  substance  exists  in  solution  in  the 
plasma,  because  some  of  the  body-fluids,  such  as  hydrocele  fluid,  con- 
taining no  platelets  or  leukocytes,  fail  to  coagulate,  although  rich  in 
fibrinogen.  The  precise  reaction  of  the  calcium  in  coagulation  has  not 
yet  been  demonstrated;  it  is  not  strictly  indispensable  to  coagulation,  for 
barium  or  strontium  may  be  made  artificially  to  replace  it.  These 
act  much  less  well  than  calcium,  however,  and  do  not  occur  in  appreciable 
amount  in  the  blood  or  the  tissues.  It  is  possible  tliat  it  may  be  the 
ionic  values  of  these  three  melats  which  are  the  determining  factors  in 
their  still  mysterious  function.  Whatever  be  the  mode  of  action,  in 
normal  coagulation  calcium  salts  of  some  kind  are  necessary.  They 
seem  to  be  antagonized  in  this  function  by  sodium  and  potasium,  a  fact 
of  possible  importance  in  explaining  the  inhibitory  influence  of  the 
endothelial  protoplasm.  The  relations  of  the  gross  elements  entering 
into  coagulation  are  almost  graphically  represented  thus : 

/Til  f  Serum 

^       ,  (Plasma  .    ^  tt-i    •    -» 
Blood-  \FibnnW,j 

'.Corpuscles     .     .      J 

The  plasma  with  the  corpuscles  constitutes  blood,  and  in  coagulation 
divides  into  serum  and  fibrin,  which  with  the  corpuscles  forms  the  clot. 

Besides  blood,  lymph,  muscle-plasma,  and  milk  normally  coagulate. 
The  lymph  clots  in  much  the  same  way  as  does  blood,  but  with  a  less 
solid  coagulum  because  of  its  lack  of  erythrocytes,  and  somewhat  more 
slowly.  Mu.scle-plasma  coagulates  in  a  similar  way,  the  clot  being 
called  myosin.  Milk  coagulates  in  the  stomach  and  duodenum  by  about 
the  same  sort  of  reaction  as  obtains  in  the  case  of  Ijlood;  rennin  is  the 
active  agent  instead  of  thrombin,  but  calcium  is  similarly  necessary. 
The  aqueous  humor  of  the  eye  and  the  pericardial  fluid  contain  no 
thrombin,  but  having  all  the  other  essentials  for  coagulation,  clot  on  the 
addifioii  of  fliis  ferment.     (See  Plale  Y.) 

The  Physical  Constitution  of  the  Blood  and  Lymph. — The  morphology 
of  the  blood  and  lymph  embraces  mainly  the  description  and  the  functions 
of  the  cor|)Uscles  contained  in  them  and  the  mechanical  relations  of  these 
coqjuscles  to  the  circulating  liquids.     We  have  already  seen  how  com- 


PLATE   V 


c 


'i^: 


w 


m 


'^m 


Typical  Blood-corpuscles,  Stained.  (R.  C.  Larrabee.) 
.4,  thrombocytes  or  platelets;  B,  erj^throcyte,  red  corpuscle;  C,  large  mononuclear 
leukocytes,  basophiles;  D,  small  mononuclear  leukocytes,  lymphocytes,  basophiles; 
E,  polymorphonuclear  leukocyte,  neutrophile;  F,  polymorphonuclear  leukocyte, 
mast-cell,  basophile;  G,  polymorphonuclear  leukocyte,  eosinophile;  H,  myelocyte; 
/,  eosinophilic  myelocyte. 


Ay/ 


FiffH. 


FigUJ 


Fc(/.vm. 


OnAWMDY  JNZ  CtlASi 


PLATE  VI 

BLOOD. 

(Ehrlicli  triple  stain.) 
(Prepared   by  Dr.  I.  P.  Lyon.) 

Fly.  I.     TYPES   OF    LEUCOCYTES, 

a.  Polymorphonuclear  Neutrophile.  6.  Polymorphonuclear  Eosinophile.  c.  Myelocyte 
(Neutrophilic),  d.  .Eosinophilic  Myelocyte,  e.  Large  Lymphocyte  (large  Mononuclear). 
/.  Small  Lymphocyte  (small  Mononuclear). 

Fig.  IL     NORMAL   BLOOD. 
Field  contains  one  neutrophile.     Reds  are  normal. 

Fig.  III.     AN^MI.A.,   POST-OPER.-VTIVE  (secondary). 

The  reds  are  fewer  than  normal,  and  are  deficient  in  haemoglobin  and  somewhat 
irregular  in  form.  One  normoblast  is  seen  in  the  field,  and  two  neutrophiles  and  oni3 
small  lymphocyte,  showing  a  marked  post-hsemorrhagic  anaemia,  with  leueoeytosis. 

Fig.  IV.     LEUCOCYTOSIS,  INFLAMMATORY. 

The  reds  are  normal.  A  marked  leueoeytosis  is  shown,  with  five  neutrophiles  and 
one  small  lymphocyte.  This  illustration  may  also  serve  the  purpose  of  showing  tha 
leueoeytosis  of  malignant  tumor 

Fig.  V.     TRICHINOSIS. 
A  marked  leueoeytosis  is  shown,  consisting  of  an  eosinophilia. 

Fig.  VI.     LYMPHATIC  LEUKyEMIA. 

Slight  anaemia.  A  large  relative  and  absolute  increase  of  the  lymphocytes  (chiefly 
the  small  lymphocytes)  is  shown. 

Fig.  VII.     SPLENO-MYELOGENOUS   LEUKEMIA. 

The  reds  show  a  secondary  anaemia.  Two  normoblasts  are  show^n.  The  leueoeytosis 
is  massive.  Twenty  leucocytes  are  shown,  consisting  of  nine  neutrophiles,  seven  myelo- 
cytes, two  small  lymphocytes,  one  eosinophile  (polymorphonuclear)  and  one  eosinophilic 
myelocyte.  Note  the  polymorphous  condition  of  the  leucocytes,  i.e.,  their  variations 
from  the  typical  in  size  and  form. 

Fig.  VIII.     VARIETIES   OF    RED    CORPUSCLES. 

a.  Normal  Red  Corpuscle  (normocyte).  h,c.  Anaemic  Red  Corpuscles,  d-g.  Poikilocytes. 
h.  Microcyte.  i.  Megaloeyte.  j-n.  Nucleated  Red  Corpuscles,  j.k.  Normoblasts  I.  Micro- 
blast,    m,  n.  Megaloblasts. 


THE  BLOOD  AND  THE  LYMPH 


263 


plicated  cliemically  these  whole  fluids  are;  we  shall  now  see  that  their 
physical  structure  is  not  less  complex  and  admirable. 

Of  whole  blood  about  45  per  cent,  by  weight  are  corpuscles  and 
55  per  cent,  plasma.  There  are  probably  three  sorts  of  corpuscles 
at  least  in  the  blood  and  lymph,  one  of  which  three  kinds  may  possibly 
consist  really  of  several  varieties.  The  life-histories  of  the  corpuscles  is 
not  yet  fully  known  with  certainty.  The  functions  of  the  various  cor- 
puscles are  somewhat  more  definitely  understood,  but  probably  tlie  leuko- 
cytes and  the  thrombocytes  at  least  have  other  uses  in  the  economy  than 
those  we  can  describe  at  present.  These  two  are  more  or  less  ameboid, 
and  exhibit  the  versatility  usual  to  little-differentiated  (?)  protoplasm. 
All  the  corpuscles  have  been  the  subject  of  a  very  large  amount  of 
research,  but  the  two  colorless  sorts,  owing  partly  perhaps  to  their 
easy  destructibility  and  to  their  relative  fewness,  have  largely  escaped 
hitherto  that  direct  observation  which  alone  could  give  adequate  knowl- 
edge of  their  functions. 


Fig.  136 


Microscopic  view  of  some  erythrocytes:    A,  on  flat;   B,  on  edge.      (Dalton.) 

The  erythrocytes,  the  colored  plastids  or  corpuscles,  are  frequently 
called  red  corpuscles  because  they  give  the  blood  its  color.  When  seen 
singly,  or  in  single  rouleaux,  however,  no  redness  is  apparent,  but,  if  any- 
thing, besides  a  pale,  straw-yellowness,  a  tinge  of  green.  To  the  histolo- 
gists  the  term  erythrocyte  indicates  still  the  embryonic  nucleated  form 
of  these  corpuscles.  The  erythrocytes  constitute  about  40  per  cent,  of 
the  weight  of  the  whole  blood.     (See  Plate  VI.) 

In  their  structure  only  three  elements  have  been  made  out:  a  very 
delicate  frame-work  of  transparent  nucleo-proteid  (globulin?)  called 
the  stroma;  90  per  cent,  of  hemoglobin,  already  described;  and  a  clear, 
glassy  envelope  of  some  gelatinous  material,  very  thin  and  flexible 
(Deetjen).  The  erythrocytes  originate  most  likely  by  the  division  of 
erythroblasts  in  the  bones'  red  marrow  and  at  first  have  nuclei.     As 


264 


THE  BLOOD  AXD  THE  LYMPH 


Fig.  137 


Cross  -  Sechon 


no  nucleus  can  be  made  out  in  the  completed  corpuscle  it  is  usually 
supposed  that  none  exists.  Fehrsen  always  found  nucleated  red  cor- 
puscles up  to  the  third  hour  after  birth.  It  is  barely  possible,  however, 
that  the  erythrocyte  has  a  nucleus  in  a  finely  divided,  scattered,  granular 
condition,  such  as  Gruber  has  called  attention  to  in  the  unicellular 
rhizopod  Pelomyxa.  The  abundance  of  nuclein  present  in  the  corpuscle 
and  the  closeness  of  its  union  with  the  hemoglobin  (see  page  256), 
tend  to  make  this  supposition  at  least  possible  and  it  has  at  present 
some  support  from  observers.      On  general  biological  principles  it  is 

more  or  less  probable,  but  inasmuch  as 
reproduction  of  the  erythrocytes  them- 
selves or  any  suggestion  of  it  has  seldom 
or  never  been  observed,  if  perfect  cells 
structurally  they  have  become  highly 
enough  differentiated  to  lose  one  of  the 
most  basal  of  cellular  functions.  The 
so-called  Poggis'  corpuscles  may  prove 
to  have  some  explanatory  value  in  this 
respect. 

In  shape  the  erythrocytes  are  biconcave 
disks  with  a  diameter  four  times  the  great- 
est thickness.  This  is  their  shape  when 
lying  flat  or  free  from  restraint,  but  they 
are  very  flexible  and  elastic  and  are  readily 
bent  nearly  double  and  distorted  in  various 
w^ays  by  the  pressure  of  the  circulation  in 
the  capillaries,  etc.  This  biconcave-disk 
shape  is  perfectly  adapted  to  best  serve 
their  function,  for  it  makes  them  at  once 
very  flexible  and  very  resilient,  and  these 
are  important  properties,  as  may  be  seen 
in  a  moment's  observation  of  the  circu- 
lation in  a  frog's  foot  or  mesentery.  It 
also  places  at  its  maximum  the  surface- 
area  which  they  expose  to  the  tissue-cells 
and  to  the  alveoli  of  the  lungs,  thus  making 
moi%  rapid  the  diffusion  and  absorption  of  oxygen  and  perhaps  of  carbon 
dioxide,  which  are  their  sole  known  functions.  Their  combined  surface- 
area  in  an  adult  of  average  size  is  not  far  from  thirty-two  hundred  square 
meters,  an  almost  astounding  figure  explained,  despite  the  extreme 
smallness  of  each  corpuscle,  by  the  fact  that  the  five  liters  of  a  man's 
blood  contains  about  twenty-five  million  million  (25,000,000,000,000)  of 
these  tiny  masses  of  oxygen-bearing  hemoglobin.  Their  shape,  more- 
over, is  that  which  exposes  a  maximum  of  surface  in  using  a  minimum 
of  hemoglobin.  Various  physical  agents,  for  example,  heat  and  elec- 
tricity, cause  the  erythrocytes  to  become  distorted  into  many  curious 
shapes,  the  most  common  of  which  is  the  crenated  form,  seen  also  as  the 


An    erythrocyte 


cross-section. 


The  triangle  a,  b,  c,  suggests  how  the 
surface-area  of  the  corpuscle  is  in- 
creased by  the  concavity  with  a  less 
amount  of  material. 


THE  BLOOD  AXD  THE  LYMPH  265 

dry  under  the  microscope.  Weidenreich  (following  Leeuwenhoek  of 
two  hundred  years  ago)  has  recently  claimed  that  the  erythrocytes  are 
normally  cup-shaped  or  even  spherical,  collapsing  quickly  when  shed. 
This  shape  may  be  readily  seen  when  the  corpuscles  are  drawn  from 
the  animal  into  an  excess  of  Senkler's  fluid.  It  is  more  likely  that  this 
shape  is  a  distortion  caused  by  the  powerful  reagents  in  a  manner  not 
unlike  the  action  of  heat  already  noted.  One  of  the  unexplained  peculiar- 
ities of  the  red  corpuscles  is  their  strong  tendency  when  shed  to  collect 
in  rouleaux  like  rolls  of  coin,  as  if  the  rims  of  these  minute  biconcave 
disks  had  some  sort  of  attraction  for  each  other. 

The  size  of  the  human  erythrocyte  is  of  considerable  medico-legal 
importance.  On  the  average  a  red  corpuscle  is  about  seven  and  seven- 
tenths  micromillimeters  (7.7  microns)  in  diameter  (a  micromillimeter 
or  micron  being  the  thousandth  part  of  a  millimeter),  and  one-quarter 

Fig.  138 


Erythrocytes  as  seen  under  certain  conditions.      This  appearance  is  the  basis  of  the  recent 
claims  that  the  normal  functioning  corpuscles  are  spherical. 

as  thick.  The  normal  variation  in  diameter  ranges  between  about  6.5 
and  9.5  microns.  AMien  the  blood  is  more  watery  than  usual  the 
corpuscles  swell,  while  fever  and  inanition  are  said  to  occasion  their 
shrinkage.  (Further  important  details  of  much  diagnostic  importance, 
concerning  the  number,  size,  and  shapes  of  the  red  corpuscles,  are  to  be 
had  from  text-books  on  hematology.) 

The  number  of  the  erythrocytes  varies  in  many  different  conditions  of 
health  as  well  as  of  disease,  but  there  is  for  each  sex  an  important  normal 
average  from  which  as  a  standard  clinical  blood-counts  are  made. 
Males  have  about  five  million  erythrocytes  to  every  cubic  millimeter 
of  their  blood  and  adult  females  about  four-and-a-ha^  millions  of  them. 
Thus  every  cubic  centimeter  of  a  man's  blood  contains  five  thousand 
million  erythrocytes. 

The  places  of  origin  of  the  red  corpuscles  in  the  fetus  seem  to  be  in  the 


266 


THE  BLOOD  AND  THE  LYMPH 


spleen,  the  liver,  the  bone-marrow,  by  division  of  the  nucleated  corpuscles 
which  are  then  present  in  the  blood,  and  perhaps  also  in  the  lymphatic 
tissue.  After  birth  it  is  probable  that  most,  if  not  all  of  the  erythrocytes 
are  formed  in  the  red  marrow  of  the  bones,  especially  in  that  of  the  skull, 
the  trunk,  and  the  ends  of  the  long  bones.  After  a  severe  hemorrhage, 
it  is  likely  that  the  yellow  marrow  also  gives  rise  to  this  sort  of  blood- 
corpuscles.  The  life-period  of  the  erythrocytes  has  not  been  definitely 
determined ,  but  it  may  be  perhaps  some  weeks  or  months. 

It  is  unlikely  that  there  is  any  place  of  destruction  of  these  corpuscles 
for  they  probably  wear  out  and  gradually  disintegrate  into  the  circula- 
tion. Nevertheless,  the  liver  undoubtedly  takes  from  the  worn-out 
corpuscles  the  portions  containing  iron  and  uses  parts  of  the  hemoglobin 
in  the  formation  of  its  bile-pigment,  bilirubin.  The  spleen  also  probably 
takes  some  of  the  iron  out  of  these  decomposing  corpuscles,  and  this 
process  may  rapidly  disintegrate  them. 


Fig.  139 


Centrosome, 


Protoplasmic 
radiation 


XucleuS' 


Lanlnnin 


Chroiiiaiiit, 


A  leukocyte  from  the  spleen  of  Proteus.      Note  the  elaborate  nucleus  and  the  centrosome. 
(Siedlocki  via  Szj'monowicz  and  McCallum.) 


The  lfx'KOCYTes  or  white  corpuscles  of  the  blood  and  lymph,  unlike 
the  red  plastids,  are  perfect  cells,  for  they  have  nuclei  as  well  as  cyto- 
plasm. 

The  leukocyte,  in  general,  is  a  minute  more  or  less  globular  mass  of 
uncolored  granular  protoplasm.  There  is  to  be  found  in  them  all  the 
elements  of  a  cell  noted  in  the  first  chapter.  They  have,  but  in  a  very 
restricted  degree,  the  same  movements  even  which  we  described  as 
characteristic  of  the  ameba.  In  size  leukocytes  vary  from  three  to 
fourteen  one-thousandths  of  a  millimeter  in  diameter.  A  fair  average 
is  ten  or  twelve  microns;  they  are  larger,  then,  than  the  red  corpuscles. 

It  is  convenient  at  the  present  time  to  riescribe  four  varieties  of  the 
leukocytes;  small  mononuclears  (lymphocytes),  large  mononuclears, 
polymorphonuclears    (myelocytes),    and   mast-cells.      The   lymphocytes 


THE  BLOOD  AND  THE  LYMPH 


267 


or  small  mononuclear  leukocytes,  as  their  name  implies,  are  the  variety 
found  largely  in  the  lymphatic  vessels  and  lymph-nodes.  They  are 
spherical,  small  cells  each  with  only  a  thin  layer  of  cytoplasm  about  the 
large  nucleus.  They  ordinarily  show  little  spontaneous  movement, 
but  Wlasson  and  Sepp  found  that  by  heating  them  to  44°  or  by  treating 
them  with  placental  tissue,  peptone,  or  farina,  they  began  to  creep 
with  ameboid  movements  as  do  the  other  sorts  of  leukocytes.  About  one- 
quarter  of  all  the  leukocytes  to  be  found  in  the  normal  blood  are  (Ehrlich) 
of  this  simple  variety.  These  originate  in  adenoid  tissue — lymph-nodes, 
spleen,  etc.  The  large  mononuclear  leukocyte  is  similar  to  the  preceding 
sort,  except  that  the  cytoplasm  is  abundant  instead  of  scanty,  while  the 
nucleus  shows  more  irregularity  in  form  and  structure.     These  may 

Fig.  140 


Section  of  a  lymph-node:  a,  fibrous  coat  which  penetrates  tlie  organ  in  the  form  of  trabecula;; 
b,  lymph-corpuscle;  c,  trabeculae  containing  blood-vessels;  d,  is  placed  in  the  medulla  of  the 
organ  in  which  will  be  seen  numerous  lymph-cords.      (Bates.) 


come  from  the  bone-marrow  or  if  not  probably  they  are  endothelial 
cells  loosened  and  floating  in  the  blood.  The  'polymorphonuclear 
leukocytes  are  well  described  by  their  name,  for  they  have  nuclei  of  very 
various  shapes,  that  of  a  sausage  or  horseshoe  being  perhaps  the 
most  common.  In  these  the  different  parts  of  the  nucleus  may  be  con- 
nected only  by  slender  bands  or  even  threads  of  nucleoplasm.  The 
cytoplasm  is  large  and  contains  fine  granules.  These  are  largely  neutro- 
philic in  their  stain-affinity,  but  some  of  them  are  the  "eosinophiles." 
These  are  the  bone-marrow's  specific  cells.  The  basophilic  leukocytes 
are  the  mast-cells.  These  are  much  like  the  preceding,  but  some  of  them 
have  several  small  nuclei  instead  of  one  large  and  segmented  nucleus. 
They  also  probably  originate  in  the  bone-marrow.' 


268  THE  BLOOD  AND  THE  LYMPH 

The  last  two  sorts  of  leukocytes  together  constitute  rather  more  than 
two-thirds  of  all  the  leukocytes,  abut  70  per  cent.,  the  mast-cells  being 
onlv  relatively  few.  They  are  the  most  active  in  their  spontaneous 
ameboid  movement.  From  1  to  4  per  cent,  of  the  polymorphonuclear 
leukocytes  contain  very  coarse  granules  of  some  material  which  has  a 
strong  aifinity  for  acid  stains.  Because  eosin  is  the  most  used  acid  dye, 
these  leukocytes  are  called  eosinophiles  or  "lovers  of  eosin."  About 
68  per  cent,  of  all  leukocytes  have  finer  granules  wdiich  greedily  absorb 
mixtures  of  acid  and  alkaline  stains,  and  they  are  accordingly  some- 
times, especially  by  pathologists,  termed  neutrophiles.  Of  all  the  white 
corpuscles,  from  0.5  to  1  per  cent,  absorb  alkaline  or  basic  stains 
into  their  coarse,  irregular  granules;  these  are  the  basophiles  or  mast- 
cells.  Wolff  maintains  that  the  lymphocytes  and  the  large  mononu- 
clears generally  contain  ephemeral  basophilic  granules,  normally  of 
much  smaller  size  than  the  others.  As  regards  nuclear  shape  and 
size  there  are  many  sorts  of  leukocytes  intermediate  between  these 
named  kinds.  This  fact  suggests  a  development  from  the  small,  round- 
nuclear  lymphocyte  (fresh  from  the  lymph  node  ?)  to  the  polynuclear  sort, 
the  nucleus  elongating,  bending,  and  gradually  breaking  apart  into 
several  separate  nuclei.  There  is  excellent  evidence,  however,  for  the 
truth  of  their  different  origins  as  stated  above.  The  "salivary  corpuscles" 
and  "colostrum  corpuscles"  are  probably  only  the  remains  of  emigrated 
leukocytes  which  have  become  vacuolated  and  divided. 

The  number  of  the  leukocytes,  like  most  facts  concerning  them, 
varies  very  widely  under  different  conditions  and  at  various  times.  It 
is  commonly  said  that  there  is  one  leukocyte  to  every  five  hundred 
erythrocytes  on  the  average  under  ordinary  conditions,  which  would 
make  about  ten  thousand  (10,000)  in  every  cubic  millimeter  of  a  man's 
blood.  During  fasting  the  ratio  lowers  to  about  one  in  seven  hundred; 
after  a  meal  it  becomes  about  one  to  three-hundred-and-fifty,  and  during 
pregnancy,  according  to  one  set  of  accounts,  it  is  one  to  two-hundred- 
and-eighty.  In  the  blood  of  the  splenic  vein  there  are  many  times  more 
leukocytes  than  in  that  of  the  splenic  artery,  and  generally  more  in 
veins  than  in  arteries.  In  various  conditions  of  disease  the  number  of 
the  leukocytes  varies  very  widely;  for  example,  in  leukemia  there  is  such 
an  increase  of  leukocytes  accompanied  by  a  decrease  of  erythrocytes 
that  the  ratio  of  the  two  may  be  as  high  as  one  to  five.  The  same 
tendency  is  seen  in  most  acute  fevers  and  in  some  inflammatory  condi- 
tions, a  fact  which  is  taken  advantage  of  for  the  early  diagnosis  of  many 
abnormal  conditions. 

The  functions  of  the  leukocytes  are  not  yet  well  known.  We  may 
mention  several,  however,  which  appear  to  be  fairly  certain.  The  most 
important  of  tliesc  perhaps  is  that  of  scavenger.  In  tliis  work  they  serve 
as  protectors  of  the  organism's  tissues  from  numerous  poisons,  organized 
and  unorganized,  and  are  then  termed  phagocytes  ("devouring  cells"). 
Scattered  about  the  tissues  and  the  circulation  in  such  enormous  numbers, 
and  with  spontaneous  movements,  they  arc  achnirably  adapted  to  serve 


THE  BLOOD  AXD  THE  LYMPH  209 

as  agents  for  the  destruction  of  any  foreign  bodies,  dead  or  alive,  to  which 
they  have  access.  Some  of  these  they  devour  as  if  taking  them  as  food, 
while  others  are  chemically  destroyed.  It  is  possible  at  least  that  they 
have  much  to  do  with  determining  the  opsonic  index  of  the  blood,  this 
being  in  a  word  the  power  of  the  latter's  resistance  to  invading  Inicteria 
and  poisons  through  the  presence  in  the  plasma  of  substances  of  unknown 
nature  termed  opsonins. 

A  second  function  of  the  leukocytes  is  undoubtetlly  to  aid  in  the 
absorption  of  fat  and  of  proteid  substances  from  the  intestine.  They 
help  also  to  carry  nutrition  from  the  tissue-capillary  to  the  tissue-cell. 
They  may  aid  in  the  coagulation  of  the  blood.  Perhaps  their  proteid s 
take  part  in  maintaining  the  normal  composition  of  the  blood,  and  it  is 
possible  that  they  contribute  carbohydrate  and  fat  as  well.  In  local 
inflammation,  when  tissue-cells  are  in  clanger  of  destruction,  they  crowd  to 
the  region  in  enormous  numbers  and  do 
their  best  to  destroy  the  invading  bacteria,  Fig.  i4i 

to  restore  to  the  endangered  cells  their 
normal    constituents,   and  in  general  to 

help  in  the  repair  of  the  injured  proto-  ^ ;, 

plasm.  Another  possible  fimction  which 
we  may  note  is  that  of  carrying  katabolic 
products  from  the  tissue-cells  into  the 
circulation  on  their  way  out  of  the  body. 

The  life-history  of  the  leukocytes  can- 
not be  written  with  any  degree  of  com- 
pleteness, but  we  know  more  about  their 
places  of  origin  than  as  to  the  way  in  '..'..i,  ^. 

which    they    disappear.  ^  phagocyte  in  the  intestinal  epithe- 

The  Thrombocytes  or  Platelets. —         lium  of  a  frog.    (Heidenhain.) 
The  physiological  status  of  these  minute 

particles  of  the  blood  is  at  present  somewhat  uncertain.  They  were 
discovered  by  Bizozero.  They  are  colorless,  jagged,  or  irregular 
masses  of  protoplasm,  very  variable  in  size,  but  averaging  not 
far  from  three  microns  in  diameter.  Early  in  the  summer  of  1906 
Wright  published  a  report  of  observations  which  seem  to  prove  beyond 
much  doubt  that  the  platelets  are  not  complete  cells,  but  that  they  may 
have  amel)oid  movements.  According  to  this  observer,  they  come  from 
the  giant-cells  (called  by  Howell  megakaryocytes)  common  in  the  bone- 
marrow  and  in  the  spleen.  These  giant-cells  are  of  spherical  form  mostly, 
but  some  of  them  "are  of  varied  and  irregular  shape  by  reason  of  the 
distortion  of  their  cytoplasm  into  processes  and  pseudopod-like  pro- 
longations of  varying  length,  form,  and  width,  so  that  they  present  all 
the  varieties  of  form  and  outline  shown  by  a  motile  ameba."  (See 
Chapter  I.)  In  some  giant-cells  nearly  all  the  cytoplasm  is  extended 
thus  as  pseudopods,  and  the  thrombocytes  are  these  pseudopodia  de- 
tached in  the  circulation.  It  is  known  that  the  giant-cells  do  lose  their 
cytoplasm  and  the  actual  movements  of  their  cytoplasm  as  well  as  that  of 


270 


THE  BLOOD  AND  THE  LYMPH 


the  platelets  may  he  seen.  In  other  respects  the  supposition  is  strongly 
corroborated,  and  altogether  it  appears  that  the  origin  of  the  thrombo- 
cytes is  now  fairly  well  established. 

Fine  granules  are  to  be  seen  in  these  corpuscles  and  indeed  these  form 
a  conspicuous  part  of  the  platelet.  The  problem  as  to  the  meaning  of 
these  granules  is  an  interesting  one.  ^^^^at  have  they  to  do  with  coagu- 
lation?   Is  it  possible  that  they  represent  a  granular  nucleus? 

Because  of  their  very  rapid  disintegration  when  blood  is  shed  and  of 
their  abundant  a<lherence  to  threads,  etc.,  suspended  in  blood,  it  has  long 
been  suspected  that  the  platelets  were  concerned  in  coagulation.  Burker 
has  now  shown  indeed  that  this  process  is  dependent  on  their  destruction 
or  solution,  as  was  described  on  page  260,  and  Ducceschi  has  corroborated 
part  of  this  result.  What  other  use  they  may  have,  if  any,  is  unsuspected 
as  vet. 


Fig.  142 


j-Jc  < 


Highly  magnified  view  in  the  spleen  of  a  salamander:    g,  capillary;   z,  pulp; 
Ic,  Ic' ,  leukocytes;  rk,  erythrocytes.      (B.  Haller.) 

Besides  the.se  three  sorts  of  relatively  substantial  structures  floating  in 
the  blood,  H.  F.  Muller  discovered  that  there  is  another  sort  which  he  calls 
hemoconia  or  blood-atoms.  They  are  much  smaller  than  the  platelets 
even.  His  claims  have  now  been  generally  substantiated  and  it  is  an 
almost  natural  probability  that  thed('l)ris  of  the  various  corpuscles  should 
persist  a  time  in  the  blood.  In  particular  the  granules  of  the  eosino- 
philic leukocytes  have  been  thought  of.  What,  if  any,  their  function  is 
no  one  as  yet  knows. 

Lymph. — For  the  causes  of  the  movement  of  the  lymph  see  the  next 
chapter;  its  chemical  composition  has  already  been  given  (page  256). 
Internal  nutrition,  the  mutual  interchanges  between  the  tissues  and  the 
circulating  bloorl,  flenotes  in  a  single  expression  the  function  of  the 
l^mph.  Lympli  is  in  nearly  all  respects  and  all  over  the  body  the  inter- 
mefJiary  between  the  blood  (the  agent,  in  a  sense,  of  external  nutrition) 
and  the  cells.     It  thus  bridges  over,  on  one  hand,  the  gap  in  the  passage 


THE  BLOOD  AND   THE  LYMPH 


271 


of  the  oxygen  and  nutrients  inward  from  the  hlood-capillaries,  and  on  the 
other  hand  that  in  the  path  of  the  carboji  dioxide,  water,  sarcolactic 
acid,  and  other  excreta  outward  from  the  varied  tissue-protoplasm  into 
the  blood-capillaries. 

The  Formation  of  Lymph. — It  is  as  important  as  it  is  difficult  to 
fully  realize  how  intimately  related  are  the  lymph  and  the  blood.  Indeed, 
as  we  have  seen,  the  former  is  almost  a  diluted  filtrate  of  the  latter,  a 
trifle  richer  in  products  of  the  tissues'  waste,  containing  more  water,  only 
by  accident  any  erythrocytes,  and  a  much  smaller  proportion  of  proteids. 


Fig.  143 


=^>  Production  of  protrypshiogeii 

(emyme). 
■^-  New  eri/tln-ocijteK. 

Destruction  of  eri/throcytes. 
^^  Prodnction  of  ttric  acid. 
■  Lymphocytes. 


Some  theories  as  to  the  functions  of  the  spleen.  The  arrows  suggest  five  of  the  uses  that 
have  been  proposed  for  this  however  still  mysterious  organ.  Smooth  muscle  is  present  in  the 
spleen,  but  what  its  motor  purpose  in  the  circulation  is  it  would  be  at  present  hard  to  define. 


It  is,  however,  very  variable  (according  to  the  metabolism)  in  all  its 
components.  Over  and  over  again  it  has  been  shown  experimentally 
that  when  crystalloids  (freely  osmosible,  soluble  substances)  are  in- 
jected into  the  circulation,  the  elapsed  time  before  they  appear  in  the 
lymph  is  inappreciable.  In  other  words  (and  this  cannot  be  too  well 
understood),  the  whole  body  is  largely  liquid,  and  especially  so  is  the 
endothelium  of  the  blood-capillaries  and  lymphatics.  The  blood  at  a 
rapid  rate  circulates  through  almost  every  minute  portion  of  the  organism 
and  makes  a  circuit  so  cjuickly  and  so  often  that,  with  the  blood-capillaries 


272  THE  BLOOD  AND   THE  LYMPH 

SO  extremely  permeable,  the  two-thirds-liquid  tissues  are  made  practically 
one,  save  as  the  selective  powers  of  the  endothelium  and  other  proto- 
plasm concerned  alter  the  intake  and  the  output  to  suit  their  own  local 
demands.  The  blood  rushing  everywhere  through  the  body,  the  ever- 
intervening  lymph,  and  the  living  tissues  form  together  a  unity  of 
semi-liquid  protoplasm  too  perfect  and  too  complicated  in  its  interactions 
for  us  at  present  to  understand  it  completely.  In  this  unity  and  in  these 
interactions  of  internal  nutrition  the  lymph  plays  the  very  important  part 
now  sufficiently  indicated.     (See  also  below,  p.  3S5.) 

The  forces  which  cause  the  passage  back  and  forth  out  of  and  into  the 
blood-capillaries,  the  lymph-spaces,  and  lymph-capillaries  need  not  be 
gone  over,  for  we  have  already  seen  practically  the  same  process  occurring 
in  the  lungs,  in  the  gut-wall,  in  the  kidneys,  etc.  It  is  apparently  a 
complex  event,  partly  filtration,  diffusion,  and  osmosis,  and  partly  a  se- 
lective, physical  sort  of  secretion.  As  we  have  said  before,  it  is  a  sort  of 
osmosis  doubtless,  but  it  is  osmosis  through  an  animal  membrane  which 
is  alive  and  which  selects  what  shall  pass  through  it.  This  selection  is 
probably  determined  more  by  the  chemical  composition  of  the  liquids 
which  pass  back  and  forth  than  merely  by  hydraulic  principles.  Perhaps 
the  ionic  dissociation  of  the  salines  and  of  the  organic  crystalloids  is 
especially  important.  We  do  not  know  to  how  great  an  extent  by  means 
of  enzymes  or  ferments  (oxidases,  digestants,  blood-pressure  raisers,  etc.), 
or  other  means  the  tissue-cells  may  determine  what  shall  pass  by  way 
of  the  lymph  into  and  out  of  them.  It  is  surely  not  wholly  a  matter  of 
selection  by  the  endothelium,  for  the  blood  on  one  side  of  the  "mem- 
brane" and  the  tissues  on  the  other  doubtless  in  a  large  measure  direct 
the  flow  of  lymph  outward  and  inward.  It  is  easy,  however,  to  carry  this 
"vitalistic"  principle  of  lymph-formation  too  far  and  to  leave  out  too 
completely  the  hydraulics  of  these  lymph-movements.  Some  in  this 
way  have  tried  to  convince  their  readers  that  lymph  is  not  "transuded 
plasma"  from  the  blood-capillaries  slightly  altered  by  the  katabolism 
and  needs  of  the  tissue  it  goes  to  and  comes  from,  but,  rather  that  it  is 
practically  sewage  from  the  tissues,  bound  outward  into  the  excreting 
blood ;  from  this  aspect  the  blood-flow  supplies  the  tissues  with  their  food. 
In  reality,  it  is  only  as  a  rude  simile  and  then  wholly  in  a  mechanical  sense 
and  for  one  functional  phase  only  that  the  lymph  may  be  said  to  be  like 
the  sewerage-plant  of  a  town.  Rather  is  it  like  a  combination,  impossible 
outside  an  organism,  of  the  Avater-supply  and  sewerage-system  of  a 
place,  and  then  only  in  a  mechanical,  not  at  all  in  a  chemical,  sense. 

Into  the  formation  of  lymph  at  least  three  processes  enter,  one  being 
physical  in  nature,  one  chemical,  and  one  probably  having  elements 
of  both  these  others.  The  physical  conditions  of  lymph-production  are 
the  pressure  and  the  flow  in  the  l)lood-capillaries;  the  cliemical  condition 
is  the  osmotic  pressure  of  the  lymph  itself,  dependent  on  molecular  and 
ionic  concentration;  the  mixed  condition  is  the  permeability  of  the  blood- 
and  lymph-capillary  walls.  The  last  is  a  matter  of  the  constitution  of 
protoplasm  not  at  present  definable,  but  without  doubt  chemophysical 


THE  BLOOD  AND  THE  LYMPH  273 

in  nature.  Heidenhain's  experiments  of  olj.striicting  the  vena  cava 
antl  tlie  abdominal  aorta  respectively  prove  that  capillary  blood-pressure 
greatly  influences  the  quantity  of  lymph  produced.  In  the  former  case 
the  lymph  from  the  trunk  was  increased  many  times;  in  the  latter  case 
is  was  decreased  in  proportion  to  the  obstruction  in  the  capillary  blo(xl- 
flow.  It  is  blood-pressure  and  blood-flow  then  that  influence  the 
filtrative  and  diffusive  elements  in  the  production  of  lymph. 

How  osmosis  is  determined  by  the  molecular  and  ionic  concentration 
of  the  plasma  and  the  lymph  has  been  discussed  elsewhere  (page  221). 
The  conditions  are,  however,  not  those  of  dead  animal  membranes  and 
of  glass  vessels,  but  of  living  endothelium  and  epithelium  under  intricate 
control.  How  far  these  diflferences  alter  the  osmosis  we  do  not  know, 
but  perhaps  not  much.  The  "membranes"  in  the  organism  are  so 
minute  and  the  forces  in  detail  so  slight  that  there  is  little  probability 
of  learning  with  present  methods  much  more  than  is  now  known  as  to  the 
details  of  the  osmotic  relations  of  these  two  similar  liquids.  Perhaps  the 
unicellular  or  other  simple  animals  may  be  made  to  tell  us  more  than  has 
yet  been  told  in  this  direction,  and  here  research  is  much  demanded. 

The  blood-capillary  wall's  permeability  is  partly  the  same  as  the  last 
condition,  for  the  wall  constitutes  one  of  the  membranes  through  which 
osmosis  must  take  place,  and  its  permeability  in  small  part  determines 
the  osmosis.  The  main  element,  however,  in  the  permeability  is  like 
secretive  function  in  that  the  protoplasm  of  the  membranes  concerned 
may  be  altered,  and  so  apparently  that  it  can  hasten  or  retard,  or  choose 
this  or  that,  according  to  local  or  to  organic  needs.  Thus,  research 
by  Galeotti  shows  that  whereas  the  permeability  of  serous  membranes 
is  not  influenced  by  their  death,  that  of  epithelium  and  endothelium  is 
greatly  altered  when  the  protoplasm  dies.  Whether  the  nervous  system 
brings  about  the  normal  condition  is  as  yet  undecided,  but  it  may  do  so 
by  the  fibrils  which  some  observers  {e.g.,  Sihler)  have  claimed  surround 
the  capillaries.  The  influence  exerted  by  the  tissue-metabolism  and  tissue- 
needs  on  lymph-production  is  direct  and  controlling,  for  it  is  to  serve  the 
tissues  that  the  lymph  exists. 

The  physical  constitution  of  lymph  is  simple,  there  being  present 
a  very  variable  plasma,  analyses  of  which  have  been  already  given 
(on  page  255),  the  lymphocytes  (small  mononuclear  leukocytes)  de- 
scribed on  page  2(36,  and  the  thrombocytes.  The  specific  gravity  of 
lymph  varies  widely,  between  1020  and  1050  perhaps.  In  color  it  is 
watery,  opalescent,  or  milky  even  after  a  fat-containing  meal,  the 
partial  opacity  being  given  by  a  varying  proportion  of  emulsion  composed 
of  particles  of  fat  much  finer  than  those  of  milk  even.  In  taste  it  is 
like  blood-plasma,  and  in  odor  nearly  so.  Owing  to  the  small  amount 
of  fibrin  which  forms  in  clotting  lymph  (0.05  per  cent.)  and  to  the  prac- 
tical absence  of  erythrocytes,  its  coagulum  is  much  less  firm  than  that 
of  blood.  Red  corpuscles  are  usually  found  in  lymph,  sometimes  enough 
to  give  it  a  pinkish  tinge,  but  these  must  be  considered  as  present  by  a 
physiological  sort  of  accident  only.  The  leukocytes  in  the  lymph  are 
is' 


274  THE  BLOOD  AND  THE  LYMPH 

present  in  very  variable  quantities  but  usually  in  numbers  not  very 
different  from  those  of  blood — namely  eight  to  twelve  thousand  per  cubic 
millimeter.     The  number  of  the  thrombocytes  has  not  been  determined. 

The  quantity  of  the  lymph  produced  and  poured  out  of  the  two 
ducts  into  the  subclavian  veins  is  commonly  stated  to  be  every  day  one- 
thirteenth  the  body's  weight.  This  is  the  same  amount  as  that  of  the 
blood  present  on  the  average  in  the  body,  or  nearly  five  liters.  Like 
everything  else  lymphatic,  this  too  is  very  variable,  for  it  depends  on 
the  general  blood-pressure,  on  the  composition  of  the  blood,  on  the 
capillarv  permeability,  on  the  nature  and  degree  of  the  metabolic  activity 
in  the  tissues.  Especially,  as  Hough  has  emphasized,  does  it  depend 
on  the  activity  of  the  skeletal  muscles,  on  the  amount  of  physical  exercise. 
Lymph  moves  in  a  sort  of  circulation  of  its  own.  It  is  passed  out  of  the 
direct  blood-circulation,  soaks  through  the  tissues,  and  afterward  enters 
again  its  system  of  "closed"  lymph-vessels  on  its  way  again  into  the  set 
of  "closed"  blood-tubes.  Because  of  this  soaking  through  the  tissue- 
protoplasm  and  of  the  inexhaustible  supply  afforded  by  the  circulating 
blood,  anything  which  increases  the  metabolism  of  much  tissue  on  the 
one  hand,  or  which  forces  mechanically  the  onward  lymph-flow  on  the 
other,  will  increase  the  quantity  of  lymph  passed  out  of  the  thoracic 
ducts.  The  muscles  constitute  half  the  mass  of  the  body  and  by  their 
activity  increase  in  both  of  the  ways  last  mentioned  the  flow  of  lymph. 
Their  heightened  metabolism  enlarges  the  demand  for  the  food-  and 
oxygen-supplying  lymph  and  their  contractions  compress  the  lymphatic 
vessels  and  so  crowd  the  lymph  onward  while  the  valves  prevent  its 
movement  in  the  backward  direction.  Measurements  have  proved 
that  an  active  muscle  exudes  five  or  six  times  as  much  lymph  as  the  same 
muscle  in  a  passive  state.  Active  muscles  then  suck  in  as  well  as  vigor- 
ouslv  press  out  a  large  amount  of  lymph,  and  the  draft  thus  produced 
cannot  fail  to  increase  the  lymph-flow  all  over  the  body.  This  means 
in  turn  not  only  a  better  cleansing  of  the  tissues  of  their  excreta,  but  a 
largely  increased  food-supply  for  them,  more  oxygen,  growth,  vigor. 
This  in  part  is  doubtless  the  reason  that  physical  exercise  plays  so  large 
a  part  in  sustaining  or  increasing  the  good  health  of  all  animals  and  of 
none  no  more  than  man,  especially  since  his  organism  hr.s  been  evolved 
on  much  more  l)0(lily  exercise  than  the  average  man  and  woman  of 
today  provides  it. 

The  functions  of  the  lymph  scarcely  need  extended  systematic 
^lescription,  for  some  of  them  have  come  out  in  the  foregoing  pages, 
namely  the  conveyance  of  food  and  of  oxygen  inward  from  the  capillaries 
to  the  cells  and  the  excretion  into  the  capillary-blood  of  the  tissues'  waste. 
It  suppHes,  then,  the  material  from  which  the  body-cells  may  feed  them- 
.selves.  There  are,  however,  at  least  four  other  lymphatic  finictions 
which  require  mention:  absor})tion  of  fat  from  the  gut;  the  lubrication  of 
the  great  serous  .surfaces;  the  maintenance  in  part  of  the  blood's  composi- 
tif)n;  anrl  the  filling  of  the  cerebral  ventricles. 

In  the  movements  of  the  viscera  on  each  other,  the  heart  between  the 


THE  BLOOD  AND  THE  LYMPH 


275 


lungs,  the  lungs  within  the  chest-walls,  the  diaphragm  over  the  abdominal 
contents,  the  abdominal  viscera  on  each  other,  the  bones  in  the  joints, 
etc.,  much  friction  would  be  caused  were  the  intervening  surfaces  not 
well  lubricated.  Luleed,  we  cannot  see  how  these  organic  movements 
could  go  on  without  this  liquid  supplied  in  just  the  right  amounts  between 
these  opposed  surfaces.  In  pleurisy,  for  example,  a  slight  roughness  is 
sometimes  produced  by  the  inflammatory  exudation  of  fibrin  on  the 
pleura,  and  the  accompanying  pain  and  disturbance  of  function  are  severe. 
The  lubricant  of  all  these  surfaces  is  lymph,  and  it  is  sometimes  said 
that  lymph  "takes  its  origin"  in  part  from  the  serous  sacs.  It  does  so 
in  a  certain  sense,  but  it  is  better  to  consider  that  it  lubricates  these 


Fin.  144 


Fig.  145 


The  structure    of    the    peritoneum:    a,    flat  The  root  of  the  aorta  from  in  front,  the  valve 

endothelial    cells;   h,    stoma.      A    lining    with        being  shut:    1,   right;  2,  left;   and  3,  posterior 
such  a  structure  is  obviously  ideally  adapted        semilunar   valve-flaps;     4,   ascending   aorta;    5 
to  be  a  lubricating  surface  between  the  ever-       and  6,  left  and  right  coronaries,  respectively, 
moving   abdominal    viscera.       Another   func-        (Rauber.) 
tion  of  the    peritoneum  is  to    shut    off    local 
inflammations,    e.  g.,    appendicitis,    from  the 
fatal  involvement    of      the    whole    abdominal 
cavity.      (Bates.) 

surfaces  and  then  osmoses  and  drains  away  in  the  lymphatic  vessels,  the 
membranes  constantly  "secreting"  their  necessary  supply  from  their 
blood-capillaries. 

Wlien  almost  any  reasonable  amount  of  harmless  liquid  (for  example 
0.06  per  cent,  aqueous  solution  of  sodium  chloride)  is  injected  into  the 
blood-vessels,  it  is  very  soon  transuded  into  the  lymph-spaces  and  into 
the  gut  and  the  blood  has  thereupon  resumed  its  normal  specific  gravity. 
Thus,  in  surgical  shock,  where  there  is  a  dangerously  low  blood-pressure 
preventing  metabolic  exchange  between  circulation  and  tissues,  the 
injection  of  Ringer's  solution  or  of  "normal  saline"  into  the  blood  raises 
its  pressure  for  only  a  few  minutes,  owing  to  this  rapid  transudation; 
the  infusion  soon  has  to  be  repeated.      In  respects  other  than  that  of 


276  THE  BLOOD  AXD  THE  LYMPH 

the  proportion  of  water  the  lymph  may  have  much  to  do  with  maintaining' 
the  blood's  composition,  but  how  much  cannot  be  stated.  There  is 
certainly  a  strong  tendency  for  the  blood  to  remain  constant,  often  ap- 
parently at  the  expense  of  the  lymph's  inconstancy.  Its  percolation 
through  the  tissues  and  its  mixture  continually  with  the  rapid  circulation 
tend  also  to  make  it  a  means  for  maintaining  the  blood's  constancy  of 
composition.  This  is  a  matter  of  no  little  importance;  the  actuation  of 
the  coordinating  nervous  system  is  dependent  on  it,  for  example,  as 
well  as  many  other  essential  processes. 

The  ventricles  of  the  cerebro-spinal  axis  are  filled  with  lymph,  but 
what  exactly,  except  to  regulate  brain-pressure,  is  the  function  of  these 
ventricles  is  uncertain.  It  is  generally  supposed  that,  in  this  process,  the 
lymph  preserves  the  requisite  pressure  perhaps  partly  by  means  of  varia- 
tion in  its  rate  of  transudation  into  and  out  of  these  cavities.  The 
exact  relation  of  the  numerous  lymphatics  of  the  brain  and  cord  to  these 
reservoirs  of  lymph  greatly  needs  working-out.  (See  also  under  the  blood- 
supply  in  the  chapter  above  on  the  nervous  system,  page  62;  and  the 
next  chapter  for  further  facts  as  to  the  relations  of  the  lymph.) 


CHAPTER    VIII. 

THE  CIRCULATION. 

We  have  now  seen  where  the  general  combined  Ijody-liquid,  the  blood 
and  lymph,  comes  from,  and  in  general  terms  its  composition.  We  must 
now  try  to  get  an  idea  of  how  and  for  what  purpose  it  goes  about  the  body. 
Few  if  any  mechanisms  with  which  we  are  familiar  are  more  complicated 
than  this,  or  do  their  work  better.  The  precise  mechanism  of  the  human 
circulation  is  described  by  visceral  and  microscopic  anatomy.  The 
chief  matters  to  be  fully  understood  from  these  other  text-books  are  the 
heart,  the  arteries,  the  capillaries,  the  lymphatics,  and  the  veins,  and  the 
relations  of  the  two  sorts  of  capillaries  to  the  tissue-cells.  The  heart  in 
man  is  a  double  force-  and  suction-pump  of  four  chambers  and  a  complex 
system  of  valves  which  are  marvels  of  hydraulic  perfection.  These  valves 
are  so  constructed  as  to  compel  the  circulation  continually  in  one  direction. 
There  are  distinct  tubes  for  the  blood  and  others  for  the  lymph,  and  both 
of  these  sorts  of  conducting  vessels  ramify  almost  endlessly  in  every 
minute  active  portion  of  the  body.  It  is  now  thought  that  the  lymph- 
system  is  a  set  of  tubes  closed  in  the  same  sense  that  the  blood  capillaries 
are  closed.  It  is  only  in  a  technical,  anatomical  sense,  however,  that 
either  the  blood-capillaries  or  the  lymph-capillaries  are  said  to  be  closed 
tubes.  Their  walls  are  so  thin  and  so  permeable  to  solutions  or  crystal- 
loids (saline  solutions)  that  the  circulating  fluid  in  them  is  in  functional 
continuity  with  the  liquid  in  the  tissue-spaces.  This  almost  complete 
unification  of  the  circulating  fluid  with  the  more  or  less  similar  fluid 
everywhere  between  the  tissue-cells  is  an  important  matter  which  must 
be  well  comprehended.  For  descriptive  purposes  these  liquids  are 
defined  as  different,  but  practically  the  blood  soaks  with  the  utmost 
freedom  into  the  tissues  and  the  lymph  collects  just  as  freely  into  the 
lymphatics.  The  exceedingly  thin  layer  of  protoplasm  which  forms 
the  blood-capillaries  and  the  lymph-capillaries  is  so  permeable  (through 
the  processes  called  filtration  and  osmosis)  that  functionally  under 
normal  conditions  it  is  almost  as  if  it  were  not  there. 

Besides  the  blood-  and  lymph-vessels  it  is  necessary  to  become  thoroughly 
familiar  with  the  elaborate  system  of  nerves  which  control  the  heart  and 
the  caliber  of  the  arteries  (and  possibly  the  permeability  of  the  capil- 
laries); but  these  cannot  be  described  here.  There  are  many  things 
also  in  the  histology  of  the  arteries,  veins,  lymphatics,  and  capillaries 
which  it  is  essential  to  have  in  mind  as  one  studies  their  functions.  Again, 
there  are  many  principles  and  facts  of  physics  connected  with  this  elabo- 
rate hydraulic   system  which  should  be  in  mind  before  studying  the 


278 


THE  CIRCULATION 


physiology  of  the  circulation.  We  are  obliged,  however,  to  confine 
ourselves  here  strictly  to  the  human  physiolog}',  and  therefore  must  omit 
more  than  this  mere  reference  to  the  structural  facts,  however  important, 
described  by  the  correlated  sciences. 

The  Causes  of  the  Circulation  are  at  least  five  in  number,  namely:  the 
contractile  energy  of  the  heart  in  systole  (contraction),  the  elastic  recoil 
of  the  arterial  walls,  the  thoracic  suction,  the  pressure  of  the  body's 
muscles  on  the  valve-supplied  veins,  and  the  suction  of  the  auricles  during 
diastole  (relaxation).  Of  these,  the  first,  chiefly  ventricular  contraction, 
unaided,  is  adequate  to  continue  the  circulation. 

The  contraction  of  the  heart  (considered  as  a  mere  pump  for 
the  present),  occurs  on  the  average  seventy-five  times  every  minute. 
The  comparatively  long  time  of  three-tenths  of  a  second  is  required  for 
he  ventricles  to  contract.     This  is  preceded  by  the  auricular  contraction 


Fig.  146 


Kl  If 


Fig.  147 
Kl         P 


***.."::,  ^.  ^"^M^IkM^^ 


^^.:^ 


^. 


^^ 


Heart-cells  of  an  adult  in  cross-section. 
(MinerviniJ 

which  lasts  one-tenth  of  a  second. 
As  already  noted,  the  auricular 
beat  merely  fills  the  ventricles  and 
for  our  present  purpose  need  not  be 
discussed.  The  ventricular  systole 
(contraction)  is  essentially  a  con- 
striction of  the  middle  layer  of  mus- 
cle-fibers. This  narrows  the  caliber 
of  the  chamber  considered  as  a  tube 
closed  at  the  lower  end  by  the  other 
layers.  The  middle  fibers  furnish  the  chief  motive  power.  The  others, 
oblique,  help  to  bring  about  the  shortening  of  the  ventricle,  the  forward 
up-rise  of  its  apex  against  the  chest-wall,  and  the  partial  descent  of  the 
heart's  base  as  the  whole  heart  twists,  shortens,  and  becomes  flatter 
antero-posteriorly.  The  exact  meaning  of  all  parts  of  the  muscular 
structure  is  not  yet  well  understood,  for  the  whole  process  is  one  of  great 
complexity,  having  in  it  the  natures  of  both  cross-striated  and  of  smooth 
mu.scle.  The  former  kind  of  muscle  causes  tlie  l)eat  and  the  latter  the 
tonus  of  the  heart.     This  tonus  is  as  yet  little  known,  but  apparently  is 


Fresh  human  heart-muscle:  K,  nucleusr 
Kl,  cement-substance;  P,  pigment-masses. 
''^Yj.        (Schiefferdecker  and  Kossel.) 


THE  CIRCULATION  279 

of  no  small  use  in  adaptinf^  blood-pressure,  etc.,  to  the  ever- varying 
organic  needs.     (See  p.  300  et  seq.) 

The  ventricles  force  into  their  respective  outlet-tubes  (against  a  pressure 
of  about  150  millimeters  of  mercury  in  the  aorta  and  of  about  50  milli- 
meters in  the  pulmonary  artery)  not  far  from  120  grams  of  blood  at  every 
contraction  (Cowl),  although  some  have  claimed  that  the  amount  of 
blood  is  less.  150  millimeters  of  mercury  exert  about  the  same  pressure 
as  would  1.92  meters  of  blood,  (taking  the  specific  gravity  of  blood  as 
1055  and  that  of  mercury  as  13.5),  so  that  the  work  done  by  the  left 
ventricle  at  each  systole  equals  that  required  to  raise  60  grams  of  Ijloofl 
1.92  meters  against  gravity,  or  0.1152  kilogram-meters  of  work.  With 
a  pulse-rate  of  75,  there  are  108,000  beats  in  twenty-four  hours,  and  the 
left  ventricle  would  do  12,441.6  kilogram-meters  of  work  daily.  If  we 
estimate  that  done  by  the  right  ventricle  as  one-third  that  by  the  left  and 
add  it  in,  we  have  16,588.8  kilogram-meters  of  work  as  that  done  by 
the  ventricles  daily.  On  the  amount  of  energy  then,  used  up  by  his 
heart's  ventricles  alone  in  one  day,  a  man  of  average  weight,  say  70  kilos, 
could  climb  237  meters  up  a  mountain;  it  is  equivalent  to  36.7  kilocalories 
of  energy.  During  severe  muscular  exertion  this  output  by  the  heart 
may  be  as  much  as  doubled  (Zuntz).  This  increase  is  accomplished 
not  only  by  a  marked  increase  in  the  pulse-rate  but  through  a  large  ex- 
pansion of  the  heart's  chambers  by  the  mechanism  which  governs  the 
tonus  of  the  heart.  Most  of  this  large  expenditure  of  energy  by  the  heart 
is  used  in  overcoming  the  friction  of  the  blood-stream  against  the  arterial 
walls. 

The  ventricular  systole  which  forces  120  cubic  centimeters  or  less  of 
blood  into  the  aorta  already  under  an  internal  tension  of  about  150 
millimeters  of  mercury,  occurs  rather  suddenly  (in  0.3  second)  and  the 
aortic  blood  is  of  necessity  quickly  displaced.  This  displacement 
occurs  not  only  in  the  aorta  but  also  in  the  pulmonary  vein  75  times  per 
minute,  and  with  such  a  frequency  even  in  rigid  tubes  there  would  be 
something  approaching  a  continuous  flow  owing  to  the  considerable 
friction.  But  the  arteries  are  quite  the  opposite  of  rigid,  for  elasticity 
combined  with  strength  is  their  most  marked  mechanical  characteristic. 
(See  the  experiments  with  the  circulation-schema  described  in  the 
Appendix.) 

The  recoil  of  the  arterial  walls,  mentioned  as  the  second  most 
important  cause  of  the  circulation,  depends  immediately  on  this  high 
elasticity,  and  must  not  be  confused  with  the  muscular  vaso-motor  con- 
traction of  the  medial  coat.  The  muscle-fibers  present  in  the  arterial 
wall  increase  somewhat  the  latter's  elasticity,  but  this  elasticity  is  mostly 
passive  and  the  recoil  is  probably  only  the  back-action  of  force  put  into 
the  arterial  wall  by  the  systolic  energy  of  the  ventricles.  The  arteries 
being  already  full,  the  accession  of  blood  at  each  beat  in  part  pushes 
forward  the  blood  already  present  and  in  part  distends  the  arteries 
(this  distention  being  the  "pulse").  Compared  with  that  of  the  aorta, 
the  diameter  of  the  single  capillaries  is  insignificant,  although  the  com- 


280  ■  THE  CIRCULATIOX 

bined  area  of  their  cross-sections  owing  to  their  multitude  is  perhaps 
several  himdred  times  that  of  the  aorta.  In  small  tubes,  however, 
friction  is  enormous  and  the  heart  has  this  friction  to  overcome  as  a 
resistance.  This  raises  the  aortic  blood-pressure  to  the  150  millimeters 
or  more  of  mercury  already  noted.  Thus,  while  the  blood  forced  into 
the  aorta  at  each  beat  pushes  some  of  the  contained  blood  onward  into 
the  smaller  arteries,  distending  them  in  turn,  some  of  the  newly  arrived 
blood  distends  the  aorta  directly.  With  a  pulse-rate  of  75  there  is  an 
interval  of  half-a-second  between  ventricular  systoles.  During  this 
half-second  the  flow  in  the  aorta  would  tend  to  slacken  and  that  in 
the  arterioles  and  capillaries  to  stop  were  it  not  for  the  energy  put 
into  the  elastic  arterial  walls  by  their  forcible  distention,  this  distention 
in  turn  being  dependent  on  the  high  resistance  of  the  minute  capillaries. 
But  immediately  the  systole  stops  this  energy  of  passive  elastic  recoil 
becomes  kinetic  and  presses  hard  upon  the  sides  of  the  cylinder  of  blood 
in  the  aorta,  etc.  Toward  the  heart  the  aortic  valves  (closed  promptly 
after  the  ventricular  systole  ended  by  the  back-pressure  beyond  them) 
shuts  off  absolutely  the  blood's  escape,  and  the  only  way  for  the  blood- 
mass  to  flow  is  toward  the  capillaries.  Thus,  while  ventricular  systole 
lasts  0.3  second,  this  strong  recoil  of  the  arterial  wall  pushes  on  the 
blood  during  the  0.5  second  which  elapses  before  another  systole  bursts 
open  the  aortic  valves  again  and  pushes  out  another  ventricleful  of 
blood  to  cause  another  pulse  throughout  the  whole  arterial  system.  (See 
the  circulation-schema  experiments  in  the  Appendix.)  It  is  to  the  high 
resistance  in  the  capillaries  and  to  the  elasticity  of  the  arteries  that  the 
constancy  of  the  flow  in  the  capillaries  is  due.  When  an  artery  is  cut, 
intermittent  spurting  of  blood  is  seen,  for  the  taking  up  of  the  inter- 
mittence  is  not  complete  until  the  capillaries  are  reached.  From  veins, 
on  the  other  hand,  except  in  abnormal  cases  of  overdilated  capillaries, 
allowing  the  pulse  to  pass  through  them,  the  flow  is  uniform  and  gentle. 

The  muscle  of  the  arterial  wall  is  used  to  maintain  the  tonus  of  the 
circulation  locally  and  to  adapt  the  latter  to  the  general  systemic  condi- 
tions. By  its  automatic  or  reflex  contraction  and  relaxation  the  caliber 
of  the  artery  is  varied  to  suit  the  manifold  conditions.  It  is  not  evident 
that  its  contraction  ever  occurs  suddenlv  enough  to  make  it  an  aid  to  the 
movement  of  the  blood  through  its  vessels.  There  is,  however,  no  actual 
evidence  that  this  sudden  vaso-constriction  does  not  occur,  especially 
under  al^normal  conditions  in  the  heart  or  the  arteries.     (See  p.  29S.) 

TnoKACic  sucTiox,  or  the  "aspiration  of  the  thorax,"  is  the  most 
powerful  of  the  three  forces  which  act  upon  and  assist  the  venous  side  of 
the  circulation.  The  physical  principles  underlying  this  suction  on  the 
veins  entering  the  boundaries  of  the  chest  have  been  gone  over  in  our 
discussion  of  respiration   ('page  110). 

The  thorax  is  an  adjustable  box  closed  save  for  the  trachea  passing 
upward  toward  the  nostrils  and  for  the  blood- and  lymph-vessels  extending 
from  it  both  upward  and  downward.  This  box  enlarges  in  every  direc- 
tion at  each  inspiration.     Much  of  the  increased  space  so  made  within  the 


THE  CIRCULATION 


281 


chest  is  filled  by  the  tidal  air.  The  same  "suction"  which  causes  the  air  to 
rush  in  throuf^h  the  trachea  inevitably  draws  also  upon  the  partly  filled 
veins,  which  extend  upward  from  the  abdomen  and  downward  from  the 
neck,  and,  by  tending  to  pull  apart  their  flaccid  walls,  sucks  inward  their 
liquid  contents  toward  the  interior  of  the  chest  and  the  heart.  The 
thoracic  space  being  increased,  fluids  under  pressure  rush  in  to  fill  it  up. 
This  same  influence  is  exerted  on  the  heart  itself,  thereby  assisting  diastole 
of  all  its  chambers,  and  also  on  the  arteries  which  enter  the  thorax. 
Because,  however,  of  their  rigid,  distended  walls  it  would  be  nearly 
ineftective  on  the  arteries,  the  balance  of  the  suction  thus  favoring  the 
circulation.  The  blood-pressure  curve  shows  plainly  that  soon  after 
the  beginning  of  inspiration  the  general  blood-pressure  begins  to  rise,  and 
that  it  reaches  its  maximum  a  short  time  after  expiration  begins.  During 
inspiration  the  pulse-rate  also  tends  to  increase,  this  being  effected  by 
some  nervous  excitation,  perhaps  by  an  overcoming  of  the  inhibitory 
influence  exerted  by  the  vagus  as  its  augmentor  fibers  are  stimulated  in 
the  expanding  alveoli,  but  perhaps,  too,  in  some  other  way. 


%, 


'W\e*^' 


I  TonuS2}ytive_q2 


Fig.  148 

SusioUc  JCafe  III. 


% 


j-i 


Dicrotic  ICat'C  IV. 


Av. 


\ 


Exp.  I     Insp.     I     Exp.     I     Insp.     \     Exp.    \     Insp.     \     Exp.     \     Insp.      \    Exp.    \Zero- 

Pressiire 

A  typical  blood-pressure  tracing  made  from  an  artery.      (Hall.) 


Co:\iPRESSiON  BY  THE  BODY-MUSCLES  of  the  valve-supplicd  veins 
is  another  factor  in  causing  the  circulation.  The  veins  are  soft  and 
easily  compressed,  being  never  normally  distended  with  blood.  The 
muscles  when  they  contract  thicken  and  harden,  and  not  only  thereby 
immediately  compress  the  veins  lying  beneath,  between,  or  within  them, 
but  they  thus  increase  the  pressure  in  the  limb  or  in  the  vicinity  and 
tend  to  cause  a  general  compression  of  the  veins  of  the  region.  Owing 
to  the  presence  of  valves  within  the  veins,  the  displacement  of  the  blood 
contained  in  these  veins  can  occur  only  in  one  direction,  and  that  always 
toward  the  heart.  As  we  have  seen  already,  this  action  is  still  more 
effective  on  the  lymphatic  system,  and  partly  because  the  valves  are  there 
much  more  numerous.  Of  course,  the  contracting  muscles  tend  to 
compress  the  arteries  nearly  as  much  as  the  veins,  and  so  to  impede 
the  circulation;  but  here  (as  in  the  last-described  cause  of  the  circulation) 
the  forcible  distention  and  incompressibility  of  the  arteries  prevent  any 
action  and  the  balance  of  efi'ect  favors  the  circulation.  In  the  hollow 
viscera  having  muscular  movements  of  their  own  this  influence  on  the 


282  THE  CIRCULATION 

veins  must  be  marked — ^for  example,  because  of  the  segmentation  and 
the  peristalsis  of  the  intestine,  and  in  the  spleen  and  uterus. 

The  suction  of  the  relaxing  auricles. — The  last  of  our  five 
causes  of  the  circulation  is  the  suction  of  the  relaxing  auricles.  This  is 
certainly  the  least  important  of  the  forces  in  action,  for  the  diastole  of 
the  auricles  is  not  a  powerful  movement,  even  the  systole  being  rela- 
tively weak.  But  the  diastole  recurs  very  frequently  and  in  itself  is 
one  of  the  constant  causes  of  the  circulation.  Moreover,  the  auricular 
expansion  is  greatly  aided  by  the  respiratory  enlargement  of  the  thorax 
as  described  above.  These  agencies  together  are  sufficient  to  produce 
in  the  vena  cava  and  auricles  of  the  dog  a  negative  pressure  equal 
to  that  of  a  few  millimeters  of  mercury,  as  has  often  been  shown  by 
manometers  connected  with  cannulse  in  the  vessels  and  auricles.  Such  a 
suction  must  have  material  influence  in  returning  the  blood  to  the 
heart  from  the  flaccid  veins  (Fig.  65) . 

Agencies  which  tend  to  retard  the  circulation  of  the  blood  are  easily 
appreciated  from  the  foregoing  facts  as  to  the  forces  which  promote  it. 
Aside  from  function,  these  naturally  are  mostly  pathological  rather  than 
normal.  Growths  on  the  heart's  valves  are  probably  the  most  frequent 
cause  of  disorder.  The  valves  on  this  account  being  hindered  from 
closing  tightly,  allow  of  regurgitation  of  the  blood  in  the  direction  opposite 
to  the  proper  circulation.  In  other  cases  the  openings  are  narrowed  by 
disease  causing  by  this  stenosis,  as  it  is  called,  an  incompleteness  in  the 
filling  of  the  ventricles  or  in  the  distention  of  the  great  arteries.  (See 
the  experiments  in  the  Appendix.)  Sometimes  the  heart-muscle  be- 
comes weakened  by  a  deposit  of  fat,  or  from  too  long-continued  overwork, 
or  from  lack  of  normal  metabolism  due  to  worry  perhaps.  Often  the 
arteries  become  hardened  (sclerosed),  so  that  they  lose  much  of  their 
essential  elasticity.  The  capillaries  may  be  far  too  permeable,  allowing 
too  much  lymph  to  soak  outward  into  the  tissues,  so  forming  edema 
(dropsy)  when  drainage  back  to  the  heart  is  poor.  Sometimes  by  local 
pressure  (as  from  a  tumor)  on  a  large  vein,  a  condition  of  venous  stasis 
is  produced,  and  occasionally  too  much  standing  gives  rise  to  a  similar 
condition  of  chronic  venous  engorgement  in  the  legs  (varicose  veins), 
man's  organism  not  yet  having  become  completely  adapted,  as  it  seems, 
to  his  recently  assumed  erect  posture. 

The  Speed  of  the  Blood-current  has  been  studied  mostly  in  the  brutes, 
and  yet  we  probably  have  a  fair  notion  of  it  as  it  is  in  man.  It  varies 
widely  in  different  places  and  at  different  times.  The  matter  is  more 
complex  than  appears  at  first  glance,  as  the  principles  of  hydraulics 
would  suggest.  All  the  considerations  concerning  speed  arc  complicated 
by  the  ever-varying  caliber  of  all  the  blood  and  lymph  vessels  except  pos- 
sil)ly  the  capillaries. 

Perhaps  a  fair  statement  of  the  average  arterial  velocity  in  man  is 
150  mm.  per  second.  It  is  much  greater  than  this  near  the  heart,  and 
very  much  less  near  the  capillaries,  for  the  friction  in  a  tube  increases 
very  greatly  with  decreasing  diameter.      In  the  aorta  the  speed  may 


THE  CIRCULATION 


283 


well  enough  be  three  times  the  average,  while  in  the  opposite  direction 
the  speed  rapidly  lessens  perhaps  to  one  three-hundredth  of  the  average. 
In  the  capillaries  then  it  has  been  estimated  that  the  blood's  velocity 
is  not  over  0.5  mm.  per  second,  which  is  about  one  mile  in  thirty-seven 
days.  The  capillaries  average  in  length  about  0.5  mm.,  so  that  the  blood- 
flow  through  the  capillaries  requires  about  one  second.  In  this  0.5  mm. 
alone  and  in  this  one  second  alone,  the  blood  is  in  practical  contact 
functionally  with  the  tissues  and  performs  promptly  all  its  varied  func- 
tions. If  one  compares  this  mile  in  thirty-seven  days  with  the  mile  in 
three  hours  which  the  blood  moves  on  the  average  in  the  arteries,  one 
has  somewhat  of  a  rough  measurement  of  the  effects  of  the  great  friction 
in  the  capillaries,  despite  the  exceedingly  smooth  surface  of  the  endodie- 
lium  in  the  tubes. 

Fig.  149 


The  blood's  pressure  as  it  varies  in  different  regions  of  the  circulation,  indicated  by  the  graphic 
method.  Abscissa  0,0,  indicates  the  regions  and  zero  pressure,  while  the  ordinate  o,h,  suggests 
the  blood-pressures  in  millimeters  of  mercury.  The  pressure  then  at  the  heart,  h,  is  about  160 
mm.  Hg.,  falling  at  first  slowly  then  rapidly  in  the  arteries  to  about  35  mm.;  ranging  thither 
to  about  15  mm.  in  the  capillaries;  while  in  the  course  of  the  veins  the  pressure  falls  to  about 
9  mm.  Hg.  less  than  zero,  the  suction  of  the  heart  in  diastole.      (Yeo.) 


In  the  veins  the  velocity  increases  rapidly  from  the  capillaries  to  the 
heart.  Probably  the  average  blood-speed  here  is  less  than  that  in  the 
arteries. 

The  Circulation-time  is  the  period  in  which  a  given  erythrocyte,  for 
example,  if  unimpeded,  can  go  from  the  heart  to  the  feet  and  back  to 
the  heart  and  thence  around  the  pulmonary  circulation.  Hering's 
experiments  showed  that  in  a  horse  the  time  required  for  the  pulmonary 
circulation  plus  the  circulation  through  the  head  was  twenty  or  thirty 
seconds,  and  Vierordt  found  the  period  in  the  dog  to  be  about  seventeen 
seconds.  Stewart  estimates  that  the  total  circulation-time  in  man  is 
about  one  minute  or  a  little  more.  These  figures  suggest  vividly  how 
active  is  the  circulation  and  how  completely  unified  by  its  means  are  the 
semi-fluid  tissue-protoplasm  and  the  circulating-liquid. 


284 


THE  CIRCULATION 


Fig 


The  Pulse-wave  is  a  rapid  impulse  sent  through  the  arteries  by  the 
ventricailar  contraction.     It  must  be  carefully  distinguished  from  the 

current  of  blood  whose  velocity  has  just 
been  mentioned.  They  have  little  in 
common,  and  yet  they  are  sometimes  at 
first  confused.  The  wave  is  accompanied 
by  a  progressive  distention  of  the  arterial 
wall,  and  travels  at  a  rate  of  from  7  to  9  m. 
per  second.  It  is  greater  in  the  upper 
extremities  than  in  the  lower  because  the 
arteries  there  are  more  elastic  than  in  the 
legs  (Zermak).  The  pulse-wave  is  at 
least  fifty  times  more  rapid  than  the 
blood-current  through  the  same  blood- 
vessel. It  is  not  to  be  found  under  ordi- 
nary conditions  in  the  capillaries  or  in 
the  veins  because  the  extreme  smallness 
of  the  former  tubes  prevents  its  passage 
through  into  the  latter.  The  length  of 
the  pulse-wave  is  about  5  m.  or  would  be 
were  the  arteries  long  enough  to  allow 
both  crests  of  the  wave  to  be  distinguished 
at  one  time.  (See  the  sphygmograms  in 
the  Appendix.) 

Blood-pressure  has  of  late  received  much 
study  from  surgeons  as  well  as  from  phy- 
siologists because  of  its  practical  impor- 
tance, especially  in  relation  to  surgical 
shock.  Blood-pressure  is  the  very  varying 
amount  of  force  exerted  laterally  by  the 
blood  against  the  M'alls  of  the  heart, 
arteries,  capillaries,  and  veins  enclosing 
it.  Highest  within  the  left  ventricle  at 
systole,  the  blood-pressure  falls  at  first 
slowly  through  the  arteries  until  the  arte- 
rioles are  reached,  when  it  falls  rapidly. 
Before  entering  the  capillaries,  80  per 
cent,  of  the  pressure  has  been  taken  up 
in  friction  and  four-fifths  of  the  total 
fall  between  the  ventricle  and  the  auricle 
again  has  occurred.  Within  the  0.5  mm. 
or  so  of  the  capillaries  10  per  cent,  more 
is  lost  and  the  blood  enters  the  veins  under 
a  pressure  of  not  more  than  10  or  20  mm. 
of  mercury.  Imoiii  here  to  the  auricle  the  fall  is  more  nearly  uniform 
than  elsewhere  in  the  circulation.  At  some  place  within  the  veins  (per- 
haps in  the  beginning  ejf  the  vena  cava)  the  blood  loses  all  its  positive 


Ludwig's  kymograph-manometer: 
a,  o',  artery  whose  pulse  and  blood- 
pressure  are  being  recorded  on  the 
smoked  drum;  the  U-tube  is  filled 
with  mercury,  the  tuh»e  between  it 
and  the  artery  with,  say  magne.sium 
sulphate  solution;  /  is  a  float,  and  .S', 
the  writing  arm;  /-"  is  a  liglit  pendu- 
lum resting  against  tlir-  arm  to  keep 
it  in  contact  with  the  drum. 


THE  CIRCULATION 


285 


pressure  when  compared  with  the  atmospheric  standard,  and  before  it 
reaches  the  auricles,  now  expanding  to  receive  it  back,  the  pressure  is  a 
negative  quantity,  that  is,  a  small  degree  of  suction. 

The  instrument  used  to  measure  blood-pressure  is  called  the  sphyg- 
mometer, and  of   this  apparatus  there  are  many  forms,  some  of  which 


Fig.  151 


Erlanger's  apparatus  for  determination  of  the  Ijlood-prtssure  in  man.  The  apparatus  is 
provided  with  a  pneumatic  cuff  (C),  which  consists  of  an  inside  rubber  bag  and  an  outside  leather 
band.  The  whole  cuff  can  be  buciiled  around  the  arm  above  the  elbow.  The  air  cavity  within 
the  rubber  bag  of  the  cuff   communicates   through  a  thick-walled  rubber  tube  and   a  four-way 

connection,  ^==ii=  with  the  three  other  essential  parts  of  the  apparatus,  namely:   (1)  downward, 

with  the  valved  bulb  {V B),  by  means  of  which  air  can  be  forced  into  the  cuff  and  can  thus  be 
made  to  compress  the  arm;  (2)  to  the  left,  with  the  mercury  manometer  {M),  from  which  the 
amount  of  pressure  applied  to  the  arm  can  be  read  directly  in  mm.  of  Hg.;  and  (3)  upward,  with 
the  distensible  bag  (B)  inside  the  glass  chamber  (G).  This  bag,  last  mentioned,  responds  to 
fluctuations  of  pressure  inside  the  rubber  bag  of  the  arm,  which  are  due  to  vibrations  of  the 
arterial  wall,  and  the  tambour  at  the  top  records  such  vibrations  on  the  drum  (D). 

are  practicable  instruments  of  no  little  use  in  surgery.  Their  practical 
use  to  the  surgeon  is  greatly  lessened  by  the  important  fact  that  the  blood- 
pressure  in  any  one  available  artery  is  little  indication  of  its  degree  in 
the  more  vital  parts  of  the  body.  It  is  indeed  a  more  variable  and  a 
more  complicated  matter  than  was  suspected  a  few  years  ago.     It  is 


286 


THE  CIRCULATION 


one  of  the  functions  of  the  elaborate  vasomotor  apparatus  always  to 
adapt  the  pressure  in  a  given  part  to  the  needs  of  that  region  at  that  time. 
The  blood-pressure  therefore  is  continually  changing  m  all  parts  of  the 
body  as  the  needs  of  different  areas  require.  Blood-pressure  in  general 
is  one  mdex  of  the  quantity  and  activity  of  the  blood-supply.  Under 
certain  conditions,  however,  the  arteries  and  arterioles  may  be  relaxed 
and  ample  blood  be  commg  to  the  part,  although  under  a  low  pressure. 
The  average  arterial  pressure  in  young  men  appears  to  lie  between 
90  and  150  mm.  of  mercury.  ]\Iental  excitement  or  fever,  for  example, 
promptly  raises  the  blood-pressure,  while  pain  lowers  it.  The  actual 
blood-pressure  in  a  vessel  at  any  time  is  the  result  of  an  hydraulic  balance 


Fig.  152 


Fig.  153 


P.Car 


111 

/I 

/ 

((\(V 

11 

m 

\ 

£. 


7^2  sec. 


Tracing  to  show  the  rise  of  pressure  in  the 
carotid  from  excitation  of  an  afferent  nerve  other 
than  the  depressor.  The  stimulus  was  applied 
at  E  and  continued  fourteen  seconds.     (Meyer.; 


Frog-cardiograms  to  .show  the  relations  of 
pulse-rate  to  the  heart-muscle's  temperature 
The  top  curve  records  the  beat  of  the  heart 
at  35°  C  the  middle  line  at  20°,  and  the 
bottom  line  at  5°.  By  the  suspension- 
method.  To  be  read  from  left  to  right.  The 
time-line  i.s  in  seconds.      Reduced. 


between  the  caliber  of  the  arteries  and  the  work  done  by  the  heart.  If 
the  arteries  are  dilated  and  the  heart  is  beating  fast  and  vigorously  the 
pressure  in  a  given  artery  may  be  the  same  as  it  would  be  if  the  artery 
were  constricted  and  the  heart  beating  slowly  and  with  less  vigor.  In 
the  capillaries  the  blood-pressure  is  from  20  to  perhaps  70  mm.  of  mercury. 
In  the  veins  it  is  from  1.5  mm.  or  so  to  a  negative  quantity  of  from  3 
to  7  mm.     (See  Fig.  149.) 

The  Pulse-rate  of  the  Heart  is  the  number  of  times  per  minute  that  it 
beats;  .sometimes  the  term  heart-rate  is  used.  In  the  average  man,  the 
pulse-rate  is  about  72  per  minute,  and  in  the  average  woman  not  far 
from  78  or  80.  As  an  average  rate  (l''^*'  niany  other  averages,  seldom 
met  with  in  fact),  we  may  use  75,  especially  because  then  by  chance  the 


THE  CIRCULATION  .  287 

various  movements  of  the  heart  occupy  periorls  of  time  which  may  be 
stated  exactly  in  whole  tenths  of  a  second.  Personal  variations  of  con- 
siderable degree  from  the  average  are  common.  Some  individuals  in 
perfect  health  exhibit  a  normal  rate  of  60,  or  even  less,  while  the  hearts 
of  others  contract  year  after  year  90  times  per  minute.  A  rate  of 
20  has  once  or  twice  been  recorded,  and  several  times  rates  of  much  over 
100.  Napoleon  exliibited  his  variation  from  the  average  of  liumanity 
by  a  pulse-rate  of  40  not  less  than  by  so  many  other  deviations. 

jNIany  sorts  of  influences  effect  the  pulse-rate,  most  of  which,  at  least, 
are  dependent  on  the  activity  of  tissue-metabolism  or  on  the  degree  of 
excitement  in  the  nervous  system,  or  on  both  of  these  at  once,  although, 
in  a  sense,  nervous  excitement  is  reducible  to  the  terms  of  tissue-metabo- 
lism. It  is,  then,  not  far  wrong  to  say  that  any  influence  or  condition 
which  increases  metabolism  to  a  considerable  degree  increases  the  heart- 
rate.  There  are  sixteen  or  seventeen  of  these  conditions  in  man  which 
may  be  noted.  ^lost  conspicuous,  perhaps,  of  these  is  age,  for  in  the 
embryo  the  heart  beats  150  times  or  so  per  minute.  The  rate  falls 
progressively  to  the  normal  adult  figures  given  above  and  rises  again 
slightly  in  old  age.  Sex  is  practically  the  next  most  important  variant 
of  the  heart-rate.  Females  have  higher  rates  than  males  of  like  age  and 
temperament.  One  sees  this  difference  not  only  as  regards  the  number 
but  as  regards  the  variability  of  the  female  rate.  Young  girls  especially 
are  subject  to  very  wide  changes  in  the  pulse-rate  in  a  purely  physio- 
logical way.  Size  influences  pulse-rate,  for  it  is  higher  in  small  than  in 
large  persons.  Temperament  is  very  effective,  slow  phlegmatic  persons 
having  a  lower  heart-rate  than  those  w^ith  short  reaction-times.  Persons 
who  are  normally  nervous  have  a  wide  range  in  their  heart-rates.  Bodily 
or  atmospheric  temperature  causes  a  variation,  a  rise  of  temperature 
within  or  without  the  body  producing  an  increase  in  the  rapidity  of  the 
heart.  Eating  increases  the  rate  for  two  hours  or  so,  until  the  activity 
of  metabolism  has  dropped  back  to  its  average.  Being  above  the  sea- 
level  increases  the  pulse-rate  because  the  necessary  increase  in  respira- 
tion demands  greater  activity  in  the  circulation.  Increase  of  respira- 
tions from  whatever  cause  tends  to  increase  the  activity  of  the  heart, 
there  being  a  tendency  to  keep  a  ratio  of  one  to  four.  Sleep  lessens  the 
heart-rate.  Muscular  exercise  increases  the  pulse-rate  markedly,  even 
up  to  200  or  more.  Posture  has  considerable  influence,  the  rate  being 
higher  when  a  person  stands  than  when  he  sits  and  lowest  when  he  is 
reclining.  Mental  excitement  increases  the  frequency  of  the  heart-rate, 
especially  in  females.  Pain  increases  the  pulse-rate  in  man,  although 
in  the  rabbit,  for  example,  it  decreases  it.  Extreme  bodily  weakness 
is  liable  to  show  increase  in  the  heart-rate.  An  increase  in  arterial  blood- 
pressure  raises  it,  the  more  rapid  rate  being  necessary  to  compensate 
for  the  increased  friction.  x\nd  many  drugs  change  the  frequency  of  the 
heart-beat  in  one  or  the  other  direction. 

These  variants  of  the  pulse-rate  are  of  much  practical  importance. 
The  more  of  them  the  phvsician  takes  into  consideration  in  estimating 


2S8 


THE  CIRCULATION 


any  given  patient's  pulse,  the  more  valuable  will  be  his  estimate  as  an 
index  of  the  latter's  condition.  The  trained  physician  and  surgeon 
take  practically  all  of  these  variants  into  consideration  without  realizing 
it  perhaps,  but  they  none  the  less  on  that  account  affect  the  estimate. 

The  Cardiac  Sequence  comprises  the  various  contractile  events  in  one 
complete  beat  of  the  heart  and  their  time-relations.  This  "cycle" 
extends  from  the  beginning  of  one  auricular  systole  to  that  of  the  next. 
We  will  take  the  average  rate  of  75  beats  per  minute  and  see  how  the 
various  parts  of  the  heart  are  differently  using  these  beat-periods.  At 
this  rate  each  beat  occupies  one  seventy-fifth  of  sixty  seconds  or  0.8 
second,  and  tenths  of  a  second  are  also  eighths  of  a  beat-period,  as  it 
very  conveniently  happens.     The  systole  of  the  auricle  (or  auricles,  for 


Fig.  154 


-^ 


YWWW^^^^- 


STLE. 


STLE. 

0.1" 


VENTRICLES. 


SYSTOLE. 
0.3' 


WHOLE   HEART.- 


liiimiii 


REPOSE  OF 

WHOLE  HEART 

0.4' 


,'^'^S■! 


PULSE  75  PER  MINUTE. 


The  cardiac  sequence.      One  beat  out  of  the  continuous  series.      The  lighter  areas, 
contraction  (systole);  the  darker  areas,  rest  or  relaxation  (diastole). 


the  two  contract  almost  exactly  together,  as  do  the  two  ventricles)  occu- 
pies, at  this  pulse-rate,  0.1  second.  Immediately  begins  the  systole  of  the 
ventricles,  and  this  requires  0.3  second,  which,  added  to  the  0.1  second, 
makes  0.4  second,  or  half  of  the  0.8  second  which  the  beat  requires. 
The  other  half  of  the  0.8  second,  0.4  second,  is  part  of  the  whole  heart's 
rest-time.  During  this  period,  as  w-ell  as  during  the  0.1  second  of  the 
succeeding  auricular  systole,  the  ventricles  arc  in  restful  diastole  while 
being  slowly  filled  with  blood  from  the  auricles  and  great  veins.  Thus, 
the  ventricles  work  in  each  beat-period  0.3  second  and  rest  the  remainder 
of  the  beat-period,  0.5  second.  The  auricles  work  only  0.1  second 
(if  we  disregard  the  possibility  of  an  active  diastole),  and  rest  during 
the  remaining  0.7  .second,  while  the  ventricles  are  both  contracting  and 
resting.     Thus  the  auricles  work  one-eighth  of  the  time  and  rest  seven- 


THE  CIRCULATION  2S9 

eighths  of  the  time;  the  ventricles  work  three-eighths  of  the  time  and  rest 
five-eightlis.  Averaging  the  rest-periods  of  the  auricles  and  of  the 
ventricles,  we  see  that  the  heart,  as  a  whole,  may  be  said  to  rest  six- 
eighths  or  three-quarters  of  every  beat-period.  We  can  no  longer  think, 
therefore,  of  the  heart  as  "an  organ  which  never  rests" — it  works, 
indeed,  only  six  hours  out  of  the  twenty-four!  A\Tien  the  rate  increases, 
the  rest-periods  are  shortened,  and  the  time  of  the  systoles  is  very  little 
decreased. 

It  is  not  known  exactly  what  proportions  of  the  0.7  second  in  the 
auricles  and  of  0.5  second  in  the  ventricles  (intervals  between  their 
respective  systoles)  are  actually  occupied  in  relaxation  or  diastole,  but 
probably  a  large  part  of  these  periods  is  so  occupied.  In  any  event, 
practically  all  of  it  is  a  period  of  rest  or  anabolism  for  the  muscle- 
protoplasm,  unless  (b,  possibility  only)  some  of  the  muscle-cells  of  the 
auricles  are  meanwhile  working  to  actively  expand  them. 

The  relations  of  the  valves'  actions  to  the  movements  of  the  chambers 
will  be  understood  if  we  go  over  somew^hat  more  in  detail  the  'phenomena 
of  the  beat.  AMiile  the  auricles  are  contracting  the  ventricles  are  having 
the  last  fifth  of  their  rest;  while  the  ventricles  are  contracting  the  auricles 
are  expanding;  after  the  contraction  of  the  ventricles  the  whole  heart  at 
once  rests  until  the  auricles  contract  again.  This  latter  contraction 
begins  in  the  great  veins,  and  extends  with  great  rapidity  over  both 
auricles  at  once  toward  the  auriculo-ventricular  groove.  This  svstole 
very  suddenly  (0.1  second)  empties  the  auricles  in  the  direction  of  the 
least  resistance — namely,  into  the  now  expanded  ventricles  through  the 
wide-open  mitral  and  tricuspid  valves.  Upward  there  is  more  resistance 
than  below,  not  so  much  because  of  the  few  valves  between  the  auricles 
and  the  veins,  as  because  the  veins  have  previously  contracted  and  so 
exert  the  resistance  of  a  column  of  blood  extending  backward,  against 
much  pressure,  even  to  the  capillaries.  It  is  likely  that  the  passive 
relaxation  of  the  very  thick  ventricular  walls  exerts  a  suction  on  the 
auricles  of  rather  more  than  23  mm.  of  mercury.  The  semilunar 
valves  are  meanwhile  shut.  The  very  sudden  and  c|uick  systole  of  the 
auricles  completely  fills  the  ventricles,  and  the  eddies  formed  by  this 
sudden  torrent  pouring  in  among  the  thickly  set  papillary  muscles, 
promptly  float  together  the  flaps  of  the  auriculo-ventricular  valves. 
The  close  apposition  of  the  edges  of  the  flaps  is  secured  by  contraction 
of  the  papillary  muscles  which  begins  (according  to  Chaveau)  in  the  very 
brief  interval  between  the  two  systoles.  As  the  ventricles  contract,  the 
auriculo-ventricular  openings  lessen,  also,  thus  tightening  still  more 
these  valves  for  the  pressure  they  are  to  withstand.  Without  appre- 
ciable pause,  the  ventricles  begin  to  contract,  but  they  occupy  thrice  as 
much  time  in  their  systole  as  do  the  auricles.  ^leanwhile,  this  strains  the 
auriculo-ventricular  valves  and  stretches  tight  the  tendinous  cords  which 
prevents  their  flaps  from  being  pushed  upward  into  the  auricles. 

As  the  ventricles  contract,  the  pressure  within  them  rapidly  rises  and 
soon  reaches  such  a  degree  that,  despite  the  pressure  in  the  great  arteries 


290 


THE  emeu  L  AT  ION 


holding  the  semihinar  valves  shut,  these  valves  are  forcibly  burst  open 
ami  the  torrent  of  blood  pours  outward  into  the  aorta  and  the  pulmonary 
arteries.  The  opening  of  these  valves  could  occur  only  when  the  pressure 
below  them  had  come  to  exceed  that  in  the  arteries  above  them — namely, 
about  200  mm.  of  mercury.  As  the  great  arteries  are  distended  with 
blood,  the  little  pouches  (sinuses  of  Valsalva)  behind  the  cups  of  the 
semilunar  valves  become  filled.  At  the  instant  when  ventricular  systole 
is  complete  and  the  pressure  in  the  ventricles  therefore  stops  rising,  more 
blood  is  forced  into  these  sinuses  by  the  instantaneous  passive  recoil 
of  the  distended  arterial  walls,  and  thus  the  cups  of  these  semilunar 
valves  are  pushed  together.  With  the  aid  of  the  corpora  Arantii  they 
quite  close  their  openings.  The  semilunar  valves  then  are  open  only 
during  the  latter  part  of  ventricular  systole,  say  for  0.2  second,  just  long 

Fig.  155 


A 

B 

c 

1 

r 

K 

i 

i 

'\ 

/ 

°y 

i\ 

1 

J 

y 

■^ 

J 

1 

U 

2 

>? 

■K 

_^ 

^ 

J^ 

v_ 

^ 

~^ 

/^ 

■^ 

— 

1 

1 

r 

1 

1 

A 

1} 

i 

1 

\^ 

^ 

f\ 

/\ 

.^\ 

1 

V 

\ 

] 

1 

\ 

1 

\ 

1 

\ 

' 

1 

\ 

1 

1 

1 

1 

_,; 

.^ 

J 

~\ 

-^ 

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s^ 

■N 

J 

K 

^ 

^ 

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^-1 

"^ 

1 

1 

1 

A 

1 

2 

?> 

1 

r 

/\ 

'\ 

/ 

"s 

s^ 

; 

/ 

J 

A 

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1 

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\ 

^ 

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p 

j- 

/ 

S 

s 

1 

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,^ 

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s 

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N, 

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^ 

Traces  showing  O,  the  auricular  pressure;    V,  the  ventricular  pressure;   and  P,  the  beat  of 
the  lieart,  together  with  their  time-relations,  in  the  horse.      (Chauveau  and  Marey.) 


enough  for  the  blood  to  be  crowded  through  them  into  the  already  dis- 
tended arteries.  The  auriculo- ventricular  (mitral  and  tricuspid)  valves 
are  closed  for  a  somewhat  longer  period — namely,  during  practically 
the  whole  of  ventricular  systole  and  for  a  brief  interval  afterward,  for 
0.4  second  perhaps  altogether.  These  two  sets  of  valves  are  open  alter- 
nately, but  never  at  the  same  time  save  for  a  specious  instant  at  the 
beginning  of  ventricular  systole  when  the  semilunars  are  already  open, 
but  the  auriculo-vrntriculars  are  not  yet  closed.  This  is  a  condition  that 
in  practice  may  or  may  not  be  present,  depending  on  the  pressure  in  the 
great  arteries  which  determines  the  time  of  opening  of  the  semilunars. 

At  once  after  ventricular  systole,  ventricular  diastole  begins  and  lasts 
about  0.5  .second,  until  the  conclusion  of  the  auricular  svstole  of  the  next 


THE  CIRCULATJOX  291 

sequence  or  beat.  During  nearly  all  this  time  the  seniilunar  valves  are 
shut  and  the  mitral  and  tricuspid  open.  This  allows  the  l)lood  constantly 
returning  to  the  heart  by  the  veins  to  pour  through  the  auricles  directly, 
it  is  likely,  into  the  ventricles.  This  flow  is  urged  by  the  suction  of  the 
expanding  auricles  during  ventricular  systole,  and  then  by  the  suction  of 
the  expanding  ventricles  themselves.  In  those  beats  which  occur  during 
inspiration,  the  enlargement  of  the  thorax  helps  the  expansion  of  all 
the  heart's  chambers,  but  the  influence  exerted  on  the  thin-walled 
auricles  is  much  greater  than  that  on  the  ventricles  whose  walls  are  many 
times  as  thick.  During  expiration,  on  the  contrary,  when  the  highly 
elastic  lungs,  etc.,  are  compressing  the  contents  of  the  chest,  the  great 
veins  and  the  auricles  share  in  the  compression,  auricular  systole  being 
aided  more  than  ventricular. 

The  various  valves  of  the  heart  are  marvels  of  mechanical  perfection. 
We  do  not  need  to  go  into  the  functional  details  of  these  organs,  however, 
for  there  is  little  about  them,  unless  it  be  the  exact  mode  of  action  of  the 
tendinous  cords,  and  papillary  muscles,  which  their  detailed  anatomy 
does  not  at  once  suggest.  When  one  remembers  that  these  complicated 
valves  act  perfectly  for  the  average  individual  more  than  a  hundred 
thousand  times  every  day,  the  wonder  is  that  valvular  heart-disease  is 
not  more  common  than  it  is,  and  sudden  death  not  much  more  frequent 
from  their  laceration  or  obstruction. 

The  Sounds  of  the  Heart  may  be  heard  plainly  by  the  ear  placed  on  any 
part  of  the  thorax,  but  most  clearly  in  front  on  either  side  of  the  sternum. 
In  number  these  souufls  are  two,  separated  by  a  short  pause,  while  a 
longer  pause  separates  those  of  one  beat  from  the  first  sound  of  the  next. 
If  we  try  to  represent  these  sounds  by  letters,  we  may  use  fiiib  and  dap 
better  than  any  others  perhaps  (the  vowel  in  the  first  being  long  and  that 
in  the  second  very  short),  while  the  interval  between  them  is  shorter  even 
than  the  second  sound. 

The  first  sound  has  given  rise  to  considerable  discussion,  especially 
as  to  its  mechanical  cause  in  the  heart.  With  a  pulse-rate  of  75,  this 
sound  lasts  about  the  same  time  as  does  the  ventricular  systole,  0.3 
second,  and  coincides  with  it  in  time.  Its  cause,  then,  is  doubtless,  in 
part  at  least,  the  powerful  contraction  of  the  three  layers  of  muscle 
composing  the  ventricles  as  they  sharply  slide  over  and  compress  one 
another  and  the  mass  of  blood  within  them. 

Within  the  ventricles  are  numerous  muscular  and  tendinous  struc- 
tures extending  nearlv  all  through  the  cavitv  of  the  ventricles,  and  these 
are  crowded  together  and  by  their  vibrations  produce  sound  as  they 
squeeze  the  blood  out  from  between  them.  Careful  analysis  of  the  sound 
w4th  resonators  has  made  obvious  two  elements:  a  sort  of  flapping  and 
string-like  tone  of  higher  pitch,  and  beneath  and  subduing  it  a  longer 
noise  more  like  a  rum])le.  The  former  part  probaljly  comes  from  the 
closure  of  the  auriculo- ventricular  valves,  and  especially  from  the  vibra- 
tion of  the  tendinous  cords  attached  to  them  and  stretched  in  both  direc- 
tions by  the  forced  closure  of  the  valve-flaps  and  the  contraction  of  the 


292  THE  CIRCULATION 

papillary  muscles  and  fleshy  columns  during  the  first  portion  of  the  systole. 
It  cannot  be  doubted  that  the  friction  of  the  heart's  apex  against  the 
chest- wall  plays  a  part  in  producing  this  sound,  and  probably  also  the 
vibration  of  the  columns  of  blood  both  within  the  ventricles  and  in  the 
first  part  of  the  great  arteries.  When  one  considers  the  extreme  and 
sudden  vigor  with  which  the  ventricles  contract,  becoming  very  tense 
and  hard,  it  is  not  difficult  to  understand  how  a  sound  is  produced. 
The  valves'  closure  has  comparatively  little  to  do  with  it,  for  when  the 
valves  are  mechanically  kept  from  closing,  the  gross  sound  is  altered 
but  little,  and  the  main  tone  persists  in  its  entirety.  That  many  elements 
enter  into  the  production  of  the  first  sound  is  certain,  and  of  these  proba- 
bly the  more  important  have  now  been  described. 

Fig.  156 


Nutrition  of  the  heart-muscle  in  the  pig;  Golgi's  method:  I,  intermuscular  spaces  from  which 
numerous  nutrition-canals  (a)  pass  into  the  muscle-fibers;  k,  blood-capillaries;  m,  sectioned 
muscle-fibers.      (Nystrom.) 

The  second  sound  follows  the  first  after  a  very  brief  interval,  perhaps 
0.1  second,  the  gradual  dying-away  of  the  first  sound  including  most 
of  this  period.  There  has  been  less  discussion  as  to  the  cause  of  the 
second  sound,  for  it  is  obviously  the  kind  of  noise  made  by  the  sudden 
closure  of  a  valve  at  the  end  of  a  tube  in  which  the  pressure  of  a  liquid  is 
high.  Furthermore,  it  occurs  just  at  the  time  when  the  two  semilunar 
valves  are  closing — namely,  just  after  the  end  of  ventricular  systole. 
It  is  then  undou})tedly  made  by  the  sudden  closure  of  these  valves.  Did 
the  pulmonary  and  the  aortic  valves  close  exactly  at  the  same  time,  this 
sound  would  be  still  shorter  and  sharper  than  it  is.  Owing,  however, 
probably  to  local  variations  in  the  pressures  within  the  aorta  and  the  pul- 


THE  CIRCULATION 

monarv  arteries  sometimes,  one  valve  may  close  a  minute 
fraction  of  a  second  before  the  others.  The  sound  is  inten- 
sified and  perhaps  altered  materially  in  tone  by  the  vibra- 
tion of  the  tense  column  of  blood  set  in  motion  by  the 
ventricular  systole  and  by  the  slapping  shut  of  the  valves 
as  the  arterial  walls  passively  (and  hence  almost  instantly) 
recoil. 

The  Heaxt-beat  as  Muscular  Action. — ^The  physiology  of 
the  heart  as  a  muscle  is  studied  in  the  laboratory  (see 
Expt.  69,  etc.,  therefore,  in  the  Appendix).  Out  of  the 
large  mass  of  facts  learned  about  the  complexities  of 
the  cardiac  muscle,  one  of  the  most  important  perhaps  is 
the  rhythmicity  apparently  inherent  in  the  heart.  Whether 
the  rhythmic  heart-beat  is  produced  by  the  action  of  the 
circulating  salines  (perhaps  through  the  ions)  on  the  heart 
muscle  directly  or  is  brought  about  by  the  rhythmic  stimu- 
lation of  nerve  cells,  as  Dogiel  has  recently  claimed  so 
vigorously,  it  is  the  most  striking  fact  in  relation  to  the 
heart.  Another  fact  about  the  heart  muscle  recently  come 
into  prominence  is  its  duality  of  action;  it  has  apparently 
the  characteristics  of  both  smooth  muscle  and  of  cross- 
striated  muscle.  The  former  kind  of  contractile  tissue  is 
represented  in  the  heart's  action  by  its  tonic  variations  in 
size.  These  occur  probably  under  the  influence  of  the  vaso- 
motor apparatus  and  correlate  its  action  with  the  caliber  of 
the  arteries.  The  cross-striated  aspect  of  the  heart-muscle 
is  represented  in  its  sharp,  quick,  and  powerful  beat.  It  is 
hoped  that  the  years  soon  to  come  will  clear  up  these 
matters  concerning  the  heart,  for  they  are  of  the  utmost 
practical  importance  to  diseased  humanity  and  in  a  theo- 
retical way  to  physiology,  striving  to  arrive  at  the  principles 
of  organic  things. 

The  Influence  of  Nerves  on  the  Heart. — AVe  do  not  yet 
know  the  exact  relations  between  the  nerves  of  the  heart 
and  its  muscle-cells.  One  h\'pothesis,  the  neurogenic  theory, 
maintains  that  the  heart's  rhythmic  boat  depends  on 
rhythmic  stimulation  from  the  central  nervous  system  or  at 
least  from  nerve  cells  in  the  heart.  The  other  supposition, 
the  myogenic  theory,  maintains  that,  provided  the  heart- 
muscle  be  supplied  with  its  nutritive  fluid  (the  blood  and  the 
lymph)  of  the  right  temperature,  etc.,  the  heart  tends  to  keep 
up  its  rhythmicity  without  continual  influence  from  the 
nervous  system.     To  the  "myogenists,"  then,  it  seems  that 


Fig.  157. — This  tracing  shows  in  an  unusual  degree  the  tonus  in  the  frog's 
heart.  Suspension-method.  To  be  read  from  left  to  right.  The  dots  are  at 
about  ten-second  intervals.      ^/^. 


294  THE  CIRCULATION 

the  nervous  system  only  controls  its  beat,  coordinating  it  with  the  needs 
of  the  organism.  The  recent  researches  of  Dogiel  and  his  colleagues 
indicate  very  strongly  that  neurones  centering  in  the  various  ganglia 
of  the  heart  itself  direct  and  perhaps  initiate  the  actual  contractions  of 
the  organ.  These  knots  of  short  neurones  are  in  the  closest  relation  with 
the  central  nervous  system,  and  it  is  with  the  latter  and  the  nerves  be- 
tween it  and  the  heart  that  we  are  chiefly  concerned.  (See  the  experi- 
ments in  the  Appendix,  page  515.)  On  the  other  hand,  the  auriculo- 
ventricular  muscle-bundle,  which  connects  intimately  and  directly  the 
inter-auricular  septum  with  the  musculature  of  the  ventricles  tends 
to  complicate  still  further  the  question  of  heart-actuation.  The  large 
number  of  facts  and  suppositions  which  have  been  accumulated  on  each 
side  of  this  far-reaching  question  of  the  relation  of  muscle  and  nerve 
remain  to  be  unified  into  the  certain  truth. 

In  general  terms  the  nervous  impulses  connected  with  the  heart  appear 
to  be  at  least  of  three  sorts.  In  the  first  place,  there  is  probably  a  set  of 
afferent  nerve-paths  (in  the  rabbit  and  dog  called  the  depressor)  which 
keep  the  central  nervous  system  informed  as  to  the  nutritive  and  hydraulic 
conditions  in  the  heart-muscle.  There  are  influences  always  coming 
to  the  heart  which  tend  to  check  its  action — namely,  the  inhibitory  influ- 
ences. And  there  are  impulses  continually  passing  to  the  heart  which 
cause  it  to  augment  its  activity. 

The  sympathetic  influence  (to  consider  the  last  first)  comes 
probablv  to  the  muscle-cells  of  the  heart  from  a  center  in  the  medulla  by 
a  route  now  fairly  well  known  in  the  dog,  rabbit,  and  cat;  it  is  doubtless 
similar  in  man.  The  fibers  bearing  these  augmentor  impulses  leave  the 
spinal  cord  by  the  anterior  roots  of  the  second  and  third,  and  perhaps 
fourth  and  fifth,  thoracic  nerves,  pass,  by  means  of  the  rami  communi- 
cantes,  to  the  ganglion  stellatum  (the  first  thoracic  ganglion  of  the  sym- 
pathetic), thence  upward  through  the  annulus  of  Vieussens  (surrounding 
the  subclavian  artery)  to  the  inferior  cervical  ganglion.  Thence,  and 
from  the  annulus  as  well,  non-medullated  fibers  pass  to  the  heart-muscle 
by  way  of  nerve-cells.  These  fibers  are  post-ganglionic  branches 
faxones)  of  cells  in  the  stellate  ganglion,  which  in  turn  are  in  close  rela- 
tion with  the  fine,  medullated,  preganglionic  fibers  coming  from  the  cord. 
In  man  these  post-ganglionic  fibers  pass  from  the  inferior  cervical 
caiiglion  and  the  annulus  in  three  groups  and  enter  the  cardiac  plexus, 
whence  they  pass  to  the  muscle-cells. 

Stimulation  with  electricity  of  these  branches  of  the  cervical  ganglion 
causes  in  the  dog  an  increase  in  the  frequency  of  the  pulse  of  even 
75  y)er  cent,  of  its  normal  rate,  while  the  force  of  the  contraction  is  also 
much  increased.  The  conductivity  of  the  heart-muscle  is  raised  also, 
and  a  negative  electric  variation  set  up  opposite  in  direction  from  that 
of  inhibition.  The  sympathetic  is  therefore  a  truly  augmentory  nerve, 
its  influence  from  the  medulla  oblongata  probably  not  only  hastening 
but  increasing  the  force  of  the  beat.  It  has  no  power,  however,  of  starting 
a  heart  which  has  stopped  all  contraction  as  seen  through  a  microscoj)e. 


THE  CIRCULATIOX  295 

The  sympathetic  exerts  its  angmentor  effect  very  slowly,  but  it  affects 
both  ventricle  and  auricle  (Gaskell). 

The  influence  of  the  vagus  on  the  heart  is  in  general  opposite 
to  that  of  the  sympathetic.  The  fine  medullated  efferent  fibers  of  the 
vagus-trunk  arise  in  the  floor  of  the  fourth  ventricle  of  the  brain  in  a 
cluster  of  nerve-cells  near  the  tip  of  the  calamus  scriptorius — not  far  then 
from  the  respiratory  centers  with  which  they  are  obviously  closely  con- 
nected functionally.  The  course  of  the  fibers  between  this  center  and 
the  heart  is  still  in  doubt.  It  is,  for  example,  not  certainly  known  as 
yet  what  relations,  if  any,  they  have  with  the  spinal  accessory.  It  is 
apparent  that  the  (preganglionic)  fibers  passing  to  the  heart-muscle  end 
in  ganglion-cells  situated  mostly  in  the  auricles,  and  that  (postganghonic) 
fibers  of  the  unmedullated  sort  pass  from  these  cells,  one  perhaps  from 
each  to  the  muscle-tissue  Here  again  there  is  difference  in  the  experi- 
mental product  of  various  researches,  and  the  anatomy  of  the  vagus 
from  brain  to  heart-cells  is  obviously  very  incomplete. 

The  action  of  the  vagus  nerve  on  the  heart  is  in  the  direction  of  a 
lessening  of  that  organ's  activity.  In  other  words,  it  is  inhibitory. 
Stimulation  of  the  vagus  produces  inhibition  in  several  respects  (Gaskell). 
It  lengthens  the  diastole  of  the  heart  and  thus  decreases  the  number 
of  beats  in  a  given  time.  It  lessens  the  force  of  systole,  making  the 
auricles  and  ventricles  contract  less  vigorously.  It  diminishes  the  tonus 
(size,  etc.)  of  the  organ.  It  decreases  the  conductivity  of  the  contractile 
impulse  to  the  muscle.  It  changes  the  electrical  state  of  the  heart- 
muscle,  making  it  more  positive. 

The  whole  subject  of  inhibition  is  a  mysterious  one,  but  its  great 
importance  as  a  mode  of  animal  functioning  becomes  continually  clearer. 
In  the  heart  one  sees  an  excellent  example  of  it,  but  how  is  it  brought 
about?  Gaskell's  trophic  theory  is  at  present  receiving  more  notice 
than  any  other  hypothesis,  and  many  things  of  different  kinds  point  to 
its  probable  truth.  This  supposition  is,  in  a  word,  that  inhibition  in  the 
heart  means  a  balance  of  the  anabolic  and  the  katabolic  processes  in  the 
nutrition  of  its  protoplasm.  Action  implies  katabolism  in  the  active 
cells,  but  an  increase  in  constructive,  anabolic  process  would  tend  to 
check  these  destructive  katabolic  changes,  to  rest  the  heart,  and  to 
increase  its  store  of  energy.  In  the  frog's  heart  one  sees  in  the  secondary 
augmentation  noted  below  evidence  that  the  organ's  energy  rises  during 
the  period  of  inhibition,  and  in  mammals  the  same  tendency  obtains. 
The  anabolic  (vagal)  influence  seems  to  interfere  more  with  the  kata- 
bolism than  does  the  katabolic  (sympathetic)  influence  with  the  anabolism 
of  the  muscle.  Until  more  than  is  now  known  is  learned  about  the 
metabolic  processes  of  muscle  in  general  little  can  be  done  to  prove  or 
to  disprove  this  interesting  theory.  It  appears  at  any  rate  to  be  a  step 
toward  the  solution  of  the  problem  of  trophic  influence  which  the  nervous 
system  is  supposed  to  exert,  and  it  may  be  useful  later  on  in  helping  out 
our  knowledge  of  secretion.  Just  now  it  is  the  easiest  way  to  explain(?) 
the  inhibition  of  the  heart  and,  by  analogy,  of  the  other  viscera. 


296  '  THE  CIRCULATION 

If  the  vagus  be  cut  within  the  skuh  of  an  animal  (amphibian  or  mam- 
mal), and  the  peripheral  stump  be  stimulated  with  an  induced  electrical 
current,  the  result  is  inhibition,  more  or  less,  of  the  heart.  The  details  of 
this  ert'ect  depend  not  only  on  the  strength  of  the  stimulus,  but  on  the 
condition,  as  well  as  the  genus,  of  the  animal.  A  latent  period  is  first 
obvious,  then  there  occurs  a  slowing  of  the  beat  (perhaps  a  stopping) 
and  a  decrease  in  the  force  of  the  contractions.  If  the  stimulation  last 
onlv  a  few  seconds,  the  inhibition  is  continued  meanwhile  and  for  a 
longer  or  a  shorter  time  after  the  former  is  stopped.  Immediately 
afterward  the  heart  gradually  increases  the  force  (extent)  of  its  contrac- 
tions until  they  may  far  exceed  their  amplitude  and  rate  before  the 
stimulation.  If  the  excitation  be  long-continued,  it  is  soon  obvious  that 
the  vagus  has  lost  control  of  the  heart,  for  despite  its  influence  the  diastoles 
shorten,  the  contractions  increase  in  force,  and  the  heart  is  soon  beating 
almost  as  if  the  vagus  were  not  conducting  inhibitory  impulses  to  it. 
This  last  phenomenon  is  due  perhaps  to  the  rhythmicity  which  is  almost 
part  of  the  muscle-cells  of  the  heart,  and  perhaps  due  to  resident 
ganglia.  It  shows  that  nothing  short  of  destruction  of  tissue  can  long 
impede  the  beating.  The  secondary  augmentation  of  the  beat  (occur- 
ring after  the  inhibition)  is  much  more  conspicuous  in  the  frog,  etc., 
than  in  the  mammal,  and  so  far  is  the  influence  of  the  vagus  over  the 
ventricles.  Indeed,  in  the  mammal  this  latter  efl:'ect  is  often  c|uite  inap- 
preciable. 

There  is  plenty  of  evidence  that  both  of  these  sets  of  nerves  are  con- 
ducting regulating  impulses  to  the  heart  continually  and  that  the  way 
the  viscus  works  is  in  a  measure  the  result  of  the  balance  between  the 
two  influences,  augmentor  and  inhibitory.  Removal  of  the  inhibitory 
factor  by  the  cutting  of  both  vagi  alone  allows  the  augmentor  to  increase 
the  rate  of  the  heart-beat.  On  the  contrary,  cutting  of  both  vagi  and 
removal  of  the  two  ganglia  in  the  course  of  the  augmentor  fibers  from 
the  cord  to  the  heart  (the  stellate  and  the  inferior  cervical  ganglia)  make 
the  organ  work  harder.  Changes  in  the  action  of  the  heart  occasioned 
reflexly  by  aft'erent  (sensory)  impulses  from  ditt'erent  parts  of  the  body 
are  sometimes  in  one  direction  and  sometimes  in  the  other,  depending 
largely  apparently  on  which  of  the  two  so-called  centers  receives  the 
stronger  impression.  This  may  be  partly  due,  however,  to  the  fact  that 
the  inhibitor  is  much  more  dependent  apparently  than  is  the  augmentor 
on  the  length  and  the  strength  of  its  stimulus.  The  latter  is  sometimes 
influenced  by  a  stimulation  so  brief  that  it  would  aflect  the  inliibitor 
little  or  not  at  all. 

The  nerves  of  the  heart  are  in  some  sort  of  connection  with  the  brain- 
cortex  as  a  whole.  In  consequence,  the  heart  may  be  readily  influenced 
by  impulses  coming  down  the  central  nervous  system  from  above  as 
well  as  bv  ail'erent  im])ulses  passing  upward.  Thus,  occasionally  one 
meets  a  person  who  can  voluntarily  slow  or  even  stop  his  heart-beat. 
It  is  possible,  indeed,  that  the  fakirs  of  India  who  put  themselves  into 
a  state  of  artificial  hibernation  for  long  periods  possess  this  dangerous 


THE  CIRCULATION  297 

faculty.  This  influence  probably  comes  primarily  from  the  cortex  of 
the  frontal  lobes.  On  the  other  hand,  many  emotions  and  mental 
excitement  in  general  hasten  the  heart,  these  impulses  coming  perhaps 
from  the  optic  thalami,  the  possible  centers  of  emotional  expression. 
Depressive  or  asthenic  emotions  (for  example,  terror)  may  inhibit  the 
heart  at  first  even  to  complete  and  sometimes  permanent  stand-still, 
as  one  sees  too  often  in  practical  jokes  with  "ghosts,"  etc.,  played  on 
"nervous"  people.     (See  Expts.  S5,  86,  and  S7,  in  the  Appendix.) 

The  afferent  nerve  of  the  heart  in  man  runs  its  fibers  in  the 
vagus  trunk,  but  in  the  rabbit  it  is  a  separate  nerve.  It  is  distributed 
over  the  ventricles,  and  centrally  seems  to  be  in  close  relation  with  the 
vasomotor  centers  located  probably  in  the  medulla.  Stimulation  of  the 
peripheral  stump  after  the  nerve  has  been  cut  gives  no  effect  appreciable, 
but  stimulation  of  the  central  stump  causes  often  a  halving  of  the  blood- 
pressure  (due  probably  to  general  vaso-dilatation)  and  a  diminution  of 
the  pulse-rate.  Both  of  these  eft'ects  are  in  the  direction  of  reducing 
the  labor  of  the  heart,  and  this  is  apparently  one  of  the  most  important 
functions  of  this  nerve.  The  depressor  seems  to  be  in  relation  with  the 
sensory  centers  of  the  brain,  for  when  the  central  stump  is  stimulated 
in  an  animal  not  unconscious  there  are  sometimes  signs  of  pain.  These 
afferent  fibers  of  the  vagus  received  their  name  "depressor"  from  the 
lowering  of  blood-pressure  which  its  stimidation  produces,  but,  as  we 
shall  soon  see,  the  same  effect  may  come  in  other  ways  which  affect  the 
vaso-motor  (vaso-dilator  ?)  centers. 

Cardiac  Centers. — As  has  been  hinted  already,  it  is  probable  that 
the  medulla  oblongata  is  the  site  of  knots  of  fibers  and  of  nerve-cells 
which  jointly  or  severally  control  the  impulses  passing  to  the  heart. 
They  also  connect  these  impulses  and  those  coming  from  the  heart  with 
other  "centers,"  especially  with  those  which  regulate  the  tonus  of  the 
blood-vessels.  The  former  conception  of  a  nerve-center  has  about  gone 
by,  leaving  us  in  ignorance  of  how  the  fibrils  of  these  various  nerves  are 
connected  in  the  medulla.  We  may  be  confident,  how^ever,  that  each 
nerve  does  not  have  a  localized  and  independent  area  of  nerve-tissue 
from  which  messages  are  sent  out  as  from  one  desk  in  a  large  telegraph 
office,  quite  independently  of  all  the  others.  The  obvious  organic 
complexity  makes  unlikely  any  such  simplicity  in  the  control  of  the  heart. 
One  must  think,  then,  of  a  center  as  an  ordered  system  of  fibers  or  of 
fibrils  dominated  in  some  way  or  ways  by  nerve-cells,  trophically,  and 
possibly  but  not  probably  as  centers  of  force. 

The  Functions  of  the  Blood-  and  Lymph-vessels. — ^These  may  well 
be  described  under  the  headings  of  the  four  sorts  of  vessels :  arteries,  capil- 
laries, lymphatics,  and  veins.  Each  takes  a  somewhat  different  part  in 
the  circulation,  although  all  of  course  are  primarily  the  distributing  tubes 
of  the  one  circulation.  Their  differences  depend  on  the  respective 
uses  of  the  vessels:  the  arteries  distribute  the  blood  in  a  complicated  way; 
the  capillaries  are  its  somewhat  loosely  defined  channels  through  the 
tissues;  the  lymphatics  return  the  osmosed  plasma  to  the  blood-vessels 


298 


THE  CIRCULATION 


^ 


k 


—^ 


proper;  and  the  veins  are  passive  completers  of  the  circulation  round  to 
the  heart  after  the  blood's  work  is  done. 

The  Physiology  of  the  Arteries. — The  structure  of  the  blood-vessels 
will  be  found  described  in  the  text-books  of  anatomy  and  of  histology. 
The  structure  of  each  sort  of  vessel  is  immediately  dependent  on  its 
functions  and  vice  versa.  The  arterial  walls  are  very  elastic  and  strong, 
and  contractile  by  means  of  the  thick  layers  of  unstriated  muscle-cells 
contained  in  them. 

In  discussing  the  causes  of  the  circulation  we  have  already  seen  in 
what  way  the  passive  elasticity  of  the  arteries  serves  the  distribution  of 
blood.  It  acts  as  a  propelling  force  during  the  five-eighths  of  the  time 
when  the  ventricles  are  not  contracting.     The  pressure  is  purely  a  passive 

recoil  of   elastic  tissues    and  not 

^iG-  158  an    active    muscular    movement. 

-^^^2^^^^=,,,^^  The  elasticity  is  of  use  furthermore 

/^^-^^^^^^J-^^^^^  ^^  allowing  of  the  distention  of  the 

arteries  to  accommodate  the  sud- 
den influx  of  blood  at  each  heart- 
beat. It  is  the  uprise  of  the 
arterial  wall  during  this  influx 
which  gives  the  pulse,  long  an 
important  practical  matter  in 
medical  art  and  science. 

The  pulse  may  be  felt  with  the 
finger  over  any  artery  not  too 
small  or  too  deeply  hidden  in  the 
body.  The  vessel  most  often  em- 
ployed for  observation  of  the  qual- 
ities of  the  pulse  is  the  radial 
artery  in  the  wrist,  although  the 
temporal  is  often  used  just  anterior 
to  the  tragus  of  the  ear,  especially 
in  case  of  children.  The  caro- 
tids at  either  side  of  and  just 
Vjelow  the  larynx  are  sometimes  convenient,  but  they  indicate  less  than 
the  others  becau.se  of  the  .soft  ti.ssues,  rather  than  bone,  behind  them. 
Wherever  it  be  felt,  the  essential  element  of  the  pulse  is  an  uprise  of  the 
arterial  wall  toward  the  finger  as  the  tube  distends  with  the  blood  pu.shed 
onward  from  the  ventricle.  The  trained  finger  readily  distinguishes 
the  gra(h)al  though  cpiifk  hardening  of  the  arterial  cylinder  and  its  more 
gra<Jual  .softening  again,  at  each  heart-beat.  The  conditions  are  such 
that  the  pulse  gives  information  not  only  concerning  the  vigor  of  the 
heart,  the  quickness  of  its  .systole,  the  pulse-rate,  and  whether  the 
valves  are  working  properly  or  not,  but  also  to  the  trained  observer  the 
.scarcely  less  important  information  as  to  the  relative  elasticity  or  rigidity 
of  the  arterial  wall,  the  tonal  size  of  the  artery,  and  the  resistance  periph- 
eral to  it.     These  .seven  relations,  and  others  of  less  practical  impor- 


Cross-section  of  medium  sized  art  .ry:  a,  endo- 
thelium cells  lining  the  lumen;  b,  internal  elastic 
membrane;  c,  subendothelial  connective  tissue; 
d,  muscle-cells  of  media;  e,  connective  tissue  of 
adventitia;   /,  vasa  vasorum.      (Bates.) 


THE  CIRCULATION 


290 


tance,  are  all  purely  mechanical  conditions  dependent  solely  on  the 
structure  and  workings  of  the  cardiac  pump  and  the  tubes  of  the  circula- 
tion.    So  much  in  the  animal  economy  depends  on  the  functions  of  the 


Fig.  159 


Section  through  the  wall  of  an  artery:  a,  endothelial  c-lls  of  intima;  b,  subendothelial  con- 
nective-tissue; c,  internal  elastic  membrane;  d,  elastic  connective-tissue;  e,  elastic  fibers  in  the 
substance  of  the  media;  f,  nuclei  of  involuntary  muscle  fibers;  g,  external  elastic  membrane; 
A,  adventitia;  i,  connective-tissue;  j,  vasa  vasorum.      (Bates.) 

heart  and  on  the  relations  of  the  blood-pressure  that  the  pulse  is  of  great 
practical  and  theoretical  importance.  The  knowledge  to  be  gained  from 
it  is  somewhat  lessened  by  the  fact  that  what  is  felt  is  the  resultant 

Fig.  160 


wmm 


mm 


iiiiiiiiiiiiiiiiiiiiiiiiiwimiiiiiiniiiiiiiimiiimii 


Tortoise  cardiograms  by  the  isolated  suspension-method  to  show  the  tonus.  The  larger  waves 
are  the  (vaso-motor?)  variations  in  tone.  To  be  read  from  left  to  right.  The  time-line  is  in 
seconds.      (See  also  Fig.  157.) 

effect,  the  balance,  of  several  combined  influences,  and  it  may  be  hard  to 
accord  this  effect  to  its  several  true  causes.  Thus,  for  example,  a  low 
peripheral  resistance  from  relaxed  capillaries  may  give  the  same  sort  of 


300  THE  CIRCULATION 

pulse  that  would  come  from  a  low  central  resistance  due,  say,  to  an  aortic- 
valve  insufficiency.  A  hard  "pulse"  (artery)  might  come  from  a  very 
^^g•orous  systole  with  low  capillary  resistance  or  from  a  much  weaker 
systole  with  narrowed  capillaries;  in  either  case,  however,  it  represents  a 
high  arterial  pressure,  whatever  the  conditions  giving  rise  to  it.  Again, 
a  very  quick  sudden  systole  would  be  partly  masked  were  the  arteries 
somewhat  inelastic  from  disease.  The  important  elements  of  blood- 
pressure  lie  largely  in  the  capillaries,  for  there  its  effects  are  exercised,  but 
the  conditions  in  the  arteries  must  be  well  understood,  because  they  supply 
the  capillaries  with  blood. 

"Whether  felt  directly  with  the  trained  finger  or  observed  indirectly  in 
the  tracing  made  by  a  mechanical  appliance  (sphygmograph),  these 
several  factors  of  the  pulse  produce  effects  which  may  be  studied,  meas- 
ured, and  compared,  and  especially  in  the  permanent  written  trace,  the 
sphygmogram. 

Fig.  161 


P.  Car. 

O.kesp.art.  O-fhs-rrwi  O.V.M 


Sphygmogram  from  a  curarized  dog  kept  alive  by  artificial  respiration  to  show  especially  the 
vaso-motor  pressure-changes:  Resp.  art.,  an  artificial  respiration  making  the  pressure  rise  and 
fall;  Vaa-mot.  and  V.  M.,  rises  and  falls  of  pressure  from  vaso-motor  changes.  (The  smallest 
waves  are  those  of  the  pulse.      Each  division  of  the  time-line  is  2  seconds.)      (Meyer.) 

Vaso-motion  is  the  narrowing  and  expanding  of  the  arterial  tubes  by 
the  contraction  and  relaxation  respectively  of  the  smooth  muscle-fibers 
in  their  walls.  It  is  then,  so  far  at  least  as  the  constriction  is  concerned, 
purely  an  active  process.  The  expansion  of  the  arteries  is  also  an  active 
process  in  its  nervous  influences  and  probably  also  in  the  action  of  the 
muscle  fibers  themselves.  Vaso-motion  then  has  to  do  with  the  tonus  of 
the  arteries.  It  must  be  carefully  distinguished  from  the  purely  passive 
enlargement  caused  by  the  heart-beat  and  from  the  perhaps  equally 
pa.ssive  narrowing  of  the  arterial  calil)er  by  the  elastic  recoil  of  the  walls 
distended  at  each  pulse.  These  distinctions,  though  basal,  are  easily 
neglected,  the  result  being  mental  confusion  as  regards  the  various 
important  forces  of  the  circulation  and  the  blood-pressure.  Va.so-motion 
is  probably  not  in  normal  cases  concerned  with  the  circulation  of  the 
bl(jod,  but  it  directly  determines  in  large  })art  the  blood-pressure.  On 
the  other  hand,  the  arterial  elasticity  is  an  important  cause  of  the  circula- 
tion, as  we  have  .seen,  and  is  also  a  factor  in  blood-pressure. 

The  exceedingly  important  functions  of  vaso-motion  are  those  on 


THE  CIRCULATION  301 

which  blood-supply  and  blood-pressure  depend.  When  a  part  becomes 
active  it  requires  more  blood  than  while  resting:  the  increase  is  supplied 
largely  by  vaso-dilatation.  Heat-regulation,  as  we  have  seen,  is  chiefly 
accomplished  by  varying  the  amount  of  blood  in  the  viscera  and  on  the 
body's  periphery  as  the  case  demands;  this  is  one  of  the  chief  uses  of  vaso- 
motion.  The  nutrition  of  the  tissues  by  the  lymph  depends  largely  on 
osmosis  from  the  capillaries,  and  this  in  turn  is  dependent  on  the  supply 
of  blood  at  the  spot  and  on  its  pressure  in  the  vessels.  The  case  is 
similar  with  glandular  action.  We  see,  therefore,  that  some  of  the  most 
fundamental  of  organic  functions  depend  sooner  or  later  on  the  relative 
caliber  of  the  arteries. 

The  mechanism  of  vaso-motion  (discovered  by  Claude  Bernard  in  1851) 
is  none  too  well  known,  but  it  is  certain  that  there  are  (autonomic) 
nerves  connected  with  the  arterial  muscle-cells  which  influence  the  latter 
to  contract  (the  vaso-constrictors),  and  that  there  are  others  which  some- 
how occasion  the  relaxation  of  the  arteries  (the  vaso-dilators).  Each  of 
these  sets  of  sympathetic  nerves  has  moreover  a  center  or  centers  in  the 

Fig    162 


An  artery  and  a  vein  from  the  stomach  of  a  frog  to  show  the  sphincters  about  them. 

^Vi.      (Mayer.) 

central  nervous  system,  w^hile  a  general  directing  vaso-motor  center  is 
probably  one  of  the  numerous  centers  of  the  medulla  oblongata.  The 
muscle-fibers  of  the  arterial  walls  are  chiefly  circular,  and  their  contrac- 
tion narrows  the  arterial  caliber.  It  has  not  been  demonstrated  as  yet 
how,  if  at  all,  nervous  influence  causes  active  relaxation  of  a  muscle 
cell.  The  process  appears  to  occur  not  only  here  but  in  the  heart-muscle, 
the  inhibitory  influence  of  the  vagus  being  perhaps  essentially  of  this 
nature  (see  above,  page  295).  Starting,  then,  wdth  an  average  tone  (or 
degree  of  contraction)  of  the  circular  fibers,  vaso-constrictor  influence 
from  the  nerves  on  Gaskell's  theory  would  increase  their  katabolism 
and  their  activity  which  is  contraction.  If,  however,  the  influence  be 
vaso-dilator,  katabolism  would  be  partly  checked  (whether  replaced  by 
anabolism  or  not)  and  the  pressure  of  the  blood  from  the  heart  would 
force  open  somewhat  the  now  relaxed  arterial  walls.  It  is  possible,  too, 
that  the  arrangement  of  the  muscular  fibers  in  the  arterial  w^all  is  such, 
(some  being  longitudinal  and  some  of  all  degrees  of  obliquity),  that  a 
positive  enlargement  of  the  tube  may  be  actively  produced  by  their  con- 


302  THE  CIRCULATION 

traction.  ^Miatever  be  the  vaso-motor  mechanism  in  the  artery,  the  two 
sorts  of  movement  and  the  normal  usual  tonus  which  is  the  balance 
between  them  are  facts  easily  observed.  See  Fig.  162  for  a  variant  of 
ordinary  vaso-motor  apparatus  found  in  an  amphibian. 

The  vaso-consiridor  centers  and  nerves  have  been  known  longer  than 
the  nervous  apparatus  of  vaso-dilatation,  but  their  exact  courses  are  still 
not  completely  understood.  There  seems  to  be  in  the  floor  of  the  fourth 
ventricle  of  the  brain  and  just  above  the  point  of  the  calamus  scriptorius 
a  nerve  "center"  whose  severance  from  the  cord  by  transverse  incision 
of  the  medulla  below  it  occasions  vaso-dilatation.  This  is  brought  about 
evidently  by  removing  from  the  arteries  concerned  the  tonic  and  continued 
vaso-constrictor  stimulus.  This  cluster  of  nerve-cells,  double  probably, 
part  on  each  side,  dominates  vaso-motion.  Its  stimulation  causes  con- 
striction. Influences  from  it  pass  downward  to  the  grey  horn  and  thence 
by  spinal  neurones  to  centers  of  more  local  influence  situated  mostly 
in  the  dorsal  sympathetic  ganglia;  thence  the  influence  passes  outward 
in  the  post-ganglionic  fibers  of  the  s}rmpathetic.  As  there  is  no  good 
evidence  of  a  general  vaso-dilator  center,  this  clump  of  cells  and  fibers  in 
an  area  of  the  medulla  a  few  millimeters  square  may  be  considered  both 
the  vaso-motor  and  the  vaso-constrictor  center,  the  latter  term  being 
preferable  as  somewhat  more  specific.  Stimulation  with  electricity  of 
this  little  region  in  the  medulla  or  of  the  ends  of  fibers  exposed  by  trans- 
verse section  just  below  it  causes  a  marked  rise  of  blood-pressure  which 
is  due  to  general  vaso-constricton.  The  nature  of  the  normal  stimidus 
is  not  understood,  but  it  is  probably  in  part  chemical  and  resident  in  the 
blood  flowing  through  it.  Besides  being  influenced  like  the  respiratory 
center  by  changes  in  the  oxygen  and  carbon  dioxide  content  of  the  blood, 
the  vaso-constrictor  center  is  promptly  stimulated  to  action  by  a  decrease 
in  the  amount  of  blood  flowing  through  it.  Its  chief  work  is  to  keep 
the  blood-supply  up  to  the  normal  standard  by  increasing  the  blood- 
pressure  when  necessary.  This  is  readily  accomplished  by  vaso-con- 
striction.  On  the  other  hand,  when  more  blood  than  is  normal  is  passing 
through  this  center  its  action  of  constriction  lessens  and  the  blood-pres- 
sure consequently  falls.  Besides  these  efferent  neural  means  there  is 
probably  a  more  or  less  elaborate  system  of  afferent  fibers  for  regulating 
the  blood-supply  of  the  various  parts  of  the  body — depressors — acting 
reflexly  on  the  constrictor  center  or  on  the  sympathetic  ganglia.  By 
being  thus  afl'ectcd  by  the  amount  and  perhaps  by  the  pressure  of  the 
blood  flowing  through  them  and  through  the  arteries,  the  double  center 
in  the  medulla  and  subsidiary  centers  in  the  cord  below  it  are  able  to 
control  the  general  Ijlood-supply. 

These  assistant  centers  probably  have  specialized  duties  for  main- 
taining the  pressure  in  various  areas,  large  or  small,  of  the  organism. 
The  impulses  connecting  them  with  the  main  center  seem  to  pass  down 
the  anterior  lateral  columns,  some  crossing  over  meanwhile.  The 
precise  locations  of  these  subsidiary  centers  have  not  been  determined, 
but  they  are  probably  in  the  anterior  horns  and  perhaps  in  part  in  the 


THE  CIRCULATION 


303 


Fig.  163 


cells  of  the  lateral  tracts.  From  them  small  meduUated  fibers  pass 
outward  as  parts  of  the  anterior  roots  and  enter  ganglia  in  the  so-called 
thoracic  sympathetic  chain  and  perhaps  elsewhere  in  the  body.  From 
these  ganglia,  probably  of  the  nature  of  locally  distributing  centers, 
unmedullated  preganglionic  fibers  convey  the  impulses  to  the  smooth 
muscle-cells  in  the  arteries,  complex  motor  end-organs  intervening 
between  the  fibers  and  the  muscle-units.  - 

The  "vaso-dilator  centers"  and  nerves  have  been  less  well  located  than 
the  preceding,  their  functional  antagonists.  Impulses  causing  vaso- 
dilatation through  a  sort  of  inhibitory  action  seem  to  arise  from  various 
regions  of  the  cord  all  the  way  from  the  medulla  to  the  sacrum.  As  is 
the  case  with  the  vaso-constrictors,  most  of  the  dilator  nerves  come  from 
the  thoracic  segments  of  the  cord  and  from  the  first  and  second  lumbar 
segments.  No  general  vaso-dilator  center  is  known.  Coming  from 
these  regions  the  fibers  pass  outward  to 
very  many  ganglia  scattered  in  different 
parts  of  the  body,  especially  of  the  trunk. 
Some  of  these  ganglia  are  large  and  some 
are  small;  some  control  single  organs  and 
others  considerable  regions  of  the  tissues 
generally.  These  fibers  bearing  vaso- 
motor impulses  between  the  cord  and 
their  destination  are  not  usually  separate 
nerves.  On  the  other  hand,  they  generally 
form  parts  of  the  complex  bundles  of 
fibers  making  up  "the  nerves"  of  the  body, 
for  these  are  mostly  bearers  of  very  many 
different  sorts  of  influences  and  messages. 
The  sciatic  nerve,  for  example,  contains 
both  kinds  of  vaso-motor  fibers,  and  the 
vaso-motor  effects  of  the  artificial  stimula- 
tion of  the  cut  sciatic  depends  on  the  ex- 
perimental conditions.  The  constrictor 
influence  usually  at  first  overpowers  the  dilator,  but  soon  becomes 
fatigued  in  some  way,  leaving  the  dilator  effect  in  control  of  the  parts 
supplied.  The  dilators,  however,  as  Bowditch  and  Warren  showed, 
are  more  susceptible  to  weak  and  relatively  infrequent  stimuli  than  are 
the  constrictor  centers.  "\Miether  the  constrictor  and  the  dilator  influ- 
ences act  continually,  making  the  tonus  of  the  arteries  thus  a  balance 
of  opposed  forces,  or  whether  (as  is  more  likely)  the  constrictor  centers 
by  themselves  control  the  tone,  the  dilatation  being  passive,  is  as  yet  un- 
certain. The  dilator-influence  on  the  latter  supposition  would  be  exerted 
only  occasionally,  when,  for  example,  rapid  or  marked  dilatation  was 
necessary  or  when  perhaps  the  blood-pressure  was  locally  too  low  to 
promptly  open  the  arteries.  Local  actions  are  probably  elaborately 
provided  for  as  regards  both  blood-pressure  and  vaso-motion.  Indeed, 
so  distinct  is  this  local  control  that  it  might  almost  be  said  that  normally 


T=2>sec 

Tracing  to  .•^liow  the  fall  of  preS" 
lire  in  the  carotid  caused  by  vaso- 
dilatation.     (Meyer.) 


304 


THE  CIRCULATION 


there  is  no  such  thing  either  as  "general  blood-pressure"  or  universal 
vaso-motion,  so  readily,  so  much,  and  so  often  do  the  local  conditions 
vary.  Each  organ  and  each  functional  group  of  cells  even,  probably 
controls  its  own  supply  of  blood  either  through  enzymes  or  by  the  action 
of  local  nerve-ganglion.     (See  also  Expt.  82  in  the  Appendix). 

Concerning  the  precise  relations  of  the  tonal  variation  in  the  size  of 
the  heart  (Figs.  157  and  160),  to  the  arterial  and  capillary  vaso-motion, 
nothing  definite  as  yet,  unfortunately,  is  known.  There  is  probably 
some  direct  reciprocal  relationship. 

The  Functions  of  the  Blood  Capillaries. — Inasmuch  as  practically  the 
whole  interchange  between  the  blood  and  the  tissues  takes  place  through 
the  capillary-walls,  it  is  obvious  that  the  functions  of  this  part  of  the 
circulation  should  be  thoroughly  known.    The  details  are  as  yet,  however. 


Fig.  164 


Capillary  vessels' 
Vasa  capillaria 


The  venous  and  arterial  networks  as  seen  in  the  corium  of  the  gastric  mucosa.      '  /].      (Toldt.) 


largely  unrevealed.  The  small  size  of  these  tubes  (less  than  a  milli- 
meter long  and  from  yinnr  to  ylir  of  a  millimeter  in  diameter)  together  with 
the  fact  that  their  functions  are  largely  based  on  molecular  movements, 
are  the  recondite  conditions  which  have  kept  the  workings  of  the  capil- 
laries doubtful  to  us.  Even  their  structure  is  not  definitely  known  in 
all  its  details,  especially  whether  a  plexus  of  nerve-fibrils  surrounds  them, 
and  what  the  nature  is  of  the  cement-substance  joining  together  the 
edges  of  the  cells.  The  protoplasm  composing  them  is  nearly  trans- 
parent and  of  extreme  thinness  anrl  apparent  simplicity,  yet  either  with 
or  without  the  influence  of  the  nervous  system  it  probably  determines 
more  than  almost  any  other  one  sort  of  tissue  the  metabolism  of  the  body, 
for  through  it  passes  the  means  by  whicli  the  body  liv(>s.  For  the  sake 
of  what  goes  on  in  the  millimeter  or  haif-uiiiliinctc  r  of  these  billions  of 
capillaries  all  the  remainder  of  the  mechani.sm  of  the  circulation  exists. 


> 

< 

-4 


THE  CIRCULATIOX 


305 


It  is  only  here  that  the  blood  performs  its  indispensable  functions.  The 
capillaries  are  the  essential  portion  of  the  circulatory  system — the  arteries 
and  veins  are  only  subsidiary  to  them. 

At  least  five  sorts  of  processes  take  place  in  the  capillaries  and  through 
its  walls.  These  are :  the  out-flow  through  the  walls  of  the  nutrient  blood 
plasma  on  the  physical  principle  of  osmosis,  determined  by  its  saline 
molecular  density ;  the  out-flow  of  oxygen  by  difl'usion ;  the  inflow  of  carbon 
dioxide  also  by  diffusion;  diapedesis  or  the  passing  through  of  the  leuko- 
cytes; and  a  probable,  but  little  known,  vaso-motion.  The  first  three  of 
these  have  already  been  explained  after  a  fashion  in  the  chapters  on 
nutrition  and  on  respiration. 


Fig.  165 


Fig.  166 


Blood-capillary:  a.  one  of  the 
endothelial  cells  which  entirely 
compose  the  tube  (unless  a  plexus 
of  nerve-fibrils  is  also  present). 
<Bates.) 


-^sP-^ 


Lymphatics  of  the  small  intestine.      (Poirier  and  Charpy.) 


The  Lymphatic  Portion  of  the  Circulation. — As  the  blood  circulates 
through  the  capillaries  only  part  of  it  at  each  passage  performs  some 
specific  function,  the  remainder  flowing  on  to  make  itself  useful  to  the 
tissues  perhaps  the  next  time  it  passes  through  capillaries.  ^Meanwhile  it 
is  carrvincr  back  to  the  heart  and  lungs  its  share  of  carbon  dioxide  and 
bearing  otf  for  excretion  into  the  kidneys  its  burden  of  dissolved  tissue- 
waste.  Of  the  capillary-blood  a  part  osmoses  through  the  thin  endothe- 
lial plates  forming  the  capillaries  to  serve  the  tissue-cells  immediately 
20 


306 


THE  CIRCULATION 


outside  in  ways  discussed  in  die  latter  part  of  the  preceding  chapter. 
It  is  this  abstracted  part  of  the  plasma,  splitting  off  from  the  circulation 
proper,  which  continually  keeps  up  the  lymph-flow.  This  is  part,  how- 
ever, properly,  of  the  hemolymph  round  from  the  ventricle  to  auricle 
again.  Let  us  examine  into  the  forces  which  cause  the  plasma  to  split 
away  from  the  circulation  proper  and  to  pass  as  lymph  so  promptly 
and  in  such  large  amounts  (five  liters  daily  at  least)  out  of  the  capillaries 
and  into  the  veins  by  this  indirect  route  of  the  tissue  cell-spaces  and  the 
lymphatics. 


Fig.  167 


acl'-\--- 


/ 

Diagram  of  a  lymph-gland  or  -node  as  seen  in  section:  vef,  efferent  lymphatics;  vaf,  afferent 
lymphatics;  bg,  blood-vessel;  k,  connective-tissue  capsule;  t,  trabeculum;  ad,  adenoid  tissue;  v, 
lymph-sr>aces;  /,  follicle  (the  essential  tissue  of  the  lymijli-gland);   n,  reticulum.      (B.  Haller.) 

Causes  of  tup:  Lymph-flow. — Four  general  causes  of  the  lymph-flow 
are  apparent,  and  we  may  speak  of  them  by  these  names:  the  pressure 
from  behind;  the  compression  f)y  muscles;  the  aspiration  of  the  thorax; 
and  the  muscular  constriction  of  the  lymphatic  walls.  Which  of  these  is 
the  most  imj)ortant  we  do  not  know,  and  in  the  absence  of  this  infor- 
mation we  may  consider  them  in  the  order  named. 

The  cause  of  the  immeth'ate  passage  of  blood-plasma  out  through  the 
capillary-wall  into  the  lymph-spaces  is  doubtless  a  complex  of  several 
forces,  physical  and  physichemical.  These  we  may  denote  as  bloods 
pressure  and  osmosis. 


THE  CIRCULATION 


307 


The  pressure  of  the  blood  within  the  capillaries  is  sufficient  to  force 
some  of  the  same  through  their  walls.  The  capillary  blood-pressure  is 
said  to  average  about  15  mm.  of  mercury  (more  at  the  arterial  end  of 
the  capillary  and  smvly  less  at  the  venous  end),  and  if  no  other  forces 
aided  these  there  would  doul)tless  be  a  slow  and  continual  soakage 
outward  into  the  tissues  wherever  a  thoroughfare  could  be  established. 
Between  the  endothelial  plates,  through  them,  or  through  the  small  rents 
which  must  continually  occur  in  them  some  plasma  would  escape  under 
this  mechanical  influence  alone.  This  process  would  be  filtration,  at 
least  in  part.  The  nature  of  osmosis  has  been  described,  and  nowhere 
does  it  occur  more  actively  or  more  importantly  than  here.  It  is  one  of 
the  most  powerful  factors  of  the  lymph-flow,  but  whether  more  so  than 
filtration  cannot  be  determined.  Its  nature  makes  of  it  under  certain 
conditions  a  force  of  enormous  power,  and  it  may  exert  a  powerful  inflii- 


FiG.  168 


Fig.  169 


Network  of 
terminal  bars  ^"^ 


Top-plate 


Intercellular  ^j 
substance 


The  lymphatics  of  the  outer  skin,  in- 
jected;   black.      5°/i.      (Rauber.) 


Diagram  of  some  columnar  epithelial  cells  to  show 
how  the  intercellular  spaces  are  shut  off  from  the 
free   surface  of    the  gland    by    the    "temiinal    bars." 

(Stohr.) 


ence  on  the  plasma  and  lymph.  It  is  dependent  not  on  differences  of 
hydraulic  pressure,  but  on  molecular  conditions  of  solution  still  open  both 
to  study  and  to  doubt.  (See  our  brief  consideration  of  osmosis  on  page 
221  and  those  following.)  It  is  to  maintain  the  normal  osmotic  pressure 
in  the  capillaries,  perhaps,  as  well  as  in  the  cells  and  elsewhere,  that  the 
salines  of  our  food  have  a  chief  usefulness. 

Having  passed  through  the  capillary-wall,  the  plasma,  now  termed 
lymph,  finds  less  resistance  beyond  than  behind,  and  so  soaks  between  the 
cells  and  out  again.  It  then  osmoses  into  freer  channels  and  into  the 
lymphatics.  The  osmosis  and  the  filtration  are  continually  going  on, 
and  they  constitute  the  continual  "force  from  behind"  which  crowds 
the  lymph  onward  through  the  tissue-chinks.  Perhaps  this  alone  would 
be  sufficient  to  continue  the  flow  even  into  the  subclavian  veins,  but 
more  likely  not,  at  least  in  that  regularity,  certainty,  and  promptness  the 
metabolic  processes  require. 


308  THE  CIRCULATION 

A  second  cause  of  the  lymph-flow  is  the  compression  of  the  lymphatics 
by  muscles.  The  system  of  the  lymphatics  ramifies  everywhere  through- 
out the  body  and  is  subject  in  very  many  places  to  compression  by  this 
means.  This  influence  is  especially  strong  probably  wherever  the  vessels 
are  crowded  against  bones,  as,  for  example,  in  the  arms,  where  contraction 
of  the  biceps,  triceps,  etc.,  compresses  lymphatics  of  considerable  size 
against  the  resistant  humerus.  In  the  legs  and  in  the  thorax  the  same 
conditions  obtain.  The  powerful  and  rapid  movements  in  the  small 
intestine  must  compress  the  villi  and  serve  to  pump  the  lymph  contained 
onward  toward  the  lymphatic  trunks.  The  reason  for  the  almost 
constant  succession  of  strong  valves  in  the  lymph-vessels  becomes  plain 
when  one  considers  the  effect  which  compression  by  the  skeletal  muscles 
would  exert  were  they  not  present.  The  lymph  in  the  vessels  would  be 
forced   in  'that   case  as  strongly  backward  as  onward.     By  the  action 

Fig.  170 


The  Rubcapillary  lympliatics  of  the  human  conjunctiva.      ™/,.      (Toldt.) 

of  these  valves,  however,  all  the  influence  exerted  is  in  the  right  flirection, 
for  regurgitation  cannot  take  place  even  to  a  small  extent  so  close  together 
are  the  valves.  The  muscles  exerting  this  motive-power  over  the  lymph 
are  practically  all  those  of  the  body,  for  even  where  no  bones  are  near, 
contraction  of  muscular  tissue  increases  the  pressure  considerably  in 
the  part  where  it  occurs.  Muscular  activity  (like  muscle-tissue  itself) 
is  much  more  universal  than  is  often  appreciated,  for  all  the  muscles 
are  continually  in  a  state  of  varying  tone  when  not  more  vigorously 
contracting. 

A  third  cause  of  the  lymph's  movement  is  the  aspiration  of  the  thorax 
as  it  is  technically  called.  This  is  the  suction  exerted  by  the  bellows- 
action  of  the  chest  at  each  respiration  on  every  vessel  entering  it  from 
without,  especially  through  the  diaj)hragm  and  from  the  neck.  This 
matter  has  been  already  dwelt  upon  in  considering  the  causes  of  the 
bloofl's  circulation  proper  (see  page  280)  and  needs  no  further  descrip- 


THE  CIRCULATION 


309 


tion  here,  for  the  influence  on  the  lynipliatics  is  identical  with  that 
exerted  on  the  veins.  It  probably  is  even  more  complete,  however,  owing 
to  the  greater  abundance  of  valves  in  the  lymphatics  than  in  the  veins. 
The  last  force  concerned  in  the  production  of  the  lymph-flow  which 
we  need  consider  is  at  present  more  or  less  problematical.  It  may  be 
mentioned,  however,  as  the  slight  constriction  of  the  lymphatics  them- 
selves by  contraction  of  the  circular  muscular  fibers  in  their  walls.  The 
relative  importance  of  this  as  a  motive  force  it  is  not  easy  to  estimate, 
but  it  undoubtedly  exists,  \^^len,  owing  to  abnormal  conditions,  the 
pressure  in  the  lymphatics  tends  to  rise  too  high,  it  may  become  an 


Fig.  171 


The  vessels  and  lymphatics  of  the  anterior  face  of  the  mammary  glands.      (Sappey.) 

important  means  of  restoring  the  onward  flow.  In  many  animals  of 
simpler  structure  than  man,  frogs,  for  example,  there  are  distinct  pulsatile 
lymph-hearts  (see  iVppendix,  page  508),  while  in  others  (e.g.,  guinea-pigs) 
the  lymph-vessels  themselves  pulsate.  Whether  or  not  such  action  is  of 
much  account  normally  in  man  remains  to  be  investigated.  Perhaps  it 
is,  especially  in  the  larger  vessels. 

Under  the  combined  influence  of  these  forces,  blood -plasma  oozes 
out  of  the  capillaries,  soaks  in  between  the  cells  composing  the  body, 
collects  by  osmosis  gradually  in  a  myriad  minute  channels,  and  makes 
its  way  more  or  less  rapidly  into  the  subclavian  veins  at  the  ba.se  of  the 


310  THE  CIRCULATION 

neck,  wliere  it  becomes  again  part  and  parcel  of  the  blood.  The  quick- 
ness with  which  the  plasma  osmoses  and  filters  outward  and  inward 
again  as  lymph  is  surprising.  The  time  varies  with  the  nature  of  the 
liquid  (colloids  not  passing  out  at  all),  but  readily  diffusible  crystaloids 
injected  into  the  blood-vessels  appear  in  the  lymph  without  any  appreci- 
able interval,  as  Colenstein  showed  and  as  is  demonstrated  frequently 
in  the  surgical  procedure.  A  minute  or  two  is  perhaps  an  average  time 
for  the  passage  outward  of  salines  from  the  capillaries.  This  shows 
in  a  striking  manner  how  unified  in  composition  at  all  times  and  under 
most  circumstances  are  the  tissue-fluids  and  the  blood. 

Edema  is  a  pathological  condition,  but  one  which  well  illustrates 
certain  principles  in  the  physiology  of  the  lymph.  It  consists  essentially 
of  a  collection  of  lymph  in  the  soft  parts  or  in  the  great  serous  sacs  of  the 
body.  It  then  has  special  names,  such  as  ascites  when  the  fluid  is 
collected  in  the  peritoneal  cavity.  The  causes  of  edema  are  various  and, 
first  or  last,  mechanical.  Thus  anything  wiiich  obstructs  the  flow  of 
Ivmph  out  of  the  tissues  into  the  veins  occasions  its  collection  among 
the  cells,  swelHng  the  part  and  making  it  obviously  more  liquid  in  com- 
position than  normally.  In  valvular  heart-disease,  owing  to  defects  in 
th?  pump  which  cripple  a  prompt  circulation  and  so  cause  venous  stasis, 
edema  is  a  frequent  symptom;  thus  people  formerly  were  said  to  die  of 
"the  dropsy."  Bright's  disease  of  the  kidneys  shows  a  similar  effect, 
but  here,  owing  to  the  incomplete  excretion  of  waste  from  the  blood,  the 
capillary  Avails  probably  become  diseased,  thus  allowing  of  the  too  great 
escape  of  more  or  less  abnormal  plasma  into  the  tissues.  In  the  ankles 
and  under  the  eyes  the  mechanical  conditions  are  such  that  here  the 
distention  makes  its  first  appearance. 

Other  matters  concerning  the  lymph  are  discussed  in  the  previous 
chapter  where  the  composition  and  functions  of  the  circulating  liquids 
are  described.  The  most  important  part  of  the  truth  about  the  lymph, 
namely,  the  exact  chemical  reactions  which  take  place  between  it  and 
the  tissue-cells,  still  remains  a  blind  secret.  From  this  view-point  the 
};hvsiology  of  the  ]ym[)h  is  almost  the  whole  science  of  organic  metabolism. 

The  Functions  of  the  Veins,  compared  with  those  of  the  arteries  and  the 
capillaries,  are  simple  and  easily  described.  One  might  almost  say  that 
the  veins  have  only  one  function,  namely,  to  return  the  blood  to  the  heart 
that  it  may  be  sent  out  again  to  perform  its  duties  in  tlie  capillaries  under 
the  control  of  the  arteries.  The  veins  outside  of  tliis  requirement  Iiave 
nearly  negative  qualities.  The  walls  are  tough,  that  they  may  stand 
when  necessary  much  pressure.  They  are  lined  with  endothelium  to 
rerhice  the  friction  and  to  perform  functions  doubtless  of  a  chemical 
nature  on  the  bloofl.  They  are  thin-vallcd  partly  because  the  low 
pressure  within  them  does  not  require  them  to  have  the  strength  coming 
from  greater  thickness,  and  partly  that  they  may  collapse  promptly 
when  severed  and  thus  prevent  death  from  air  sucked  into  the  heart 
from  wounds,  'flicy  are  capacious  (two  or  Uirec  or  even  more  times  as 
spacious  as  the  arteries),  in  order  tliat  tiie  friction  of  the  blood  within 


THE  CIRCULATION  311 

them  may  be  lessened  ami  the  speed  therefore  as  great  as  possible.  They 
are  situated  oftentimes  superficially,  because,  from  the  teleological  point 
of  view  at  least,  injury  to  them  from  without  is  much  less  dangerous  than 
a  similar  wound  of  an  artery  would  be,  owing  to  the  relatively  small 
pressure  within  them.  The  veins  are  furnished  with  valves  lest  local 
conditions  of  muscular  compression  or  pressure  from  other  causes  would 
interfere  with  the  round  of  the  blood  in  a  prompt  and  complete  manner. 
Whatever  the  source  of  external  compression,  when  valves  are  present 
the  circulation  is  not  hindered  but  rather  helped.  Another  use  of  the 
valves  is  seen  especially  in  the  legs :  were  they  not  present  the  veins  of  the 
feet  would  have  to  support  a  column  of  blood  a  meter  or  more  high. 
This  would  not  only  fill  them  so  full  as  to  impede  the  movements  of  the 
blood  by  friction,  but  it  would  compel  an  unnecessary  resistance  for  the 
heart  and  the  other  forces  causing  the  circulation  to  overcome.  As  it  is, 
no  portion  of  the  great  leg-veins  supports  more  than  a  very  short  column 
of  blood  even  when  the  man  is  standing,  for  the  support  is  divided  among 
manv  valves. 


CHAPTER    IX. 


THE   SKIN. 


It  is  much  easier  to  imder-estimate  than  to  over-estimate  the  impor- 
tance of  the  functions  of  the  human  skin  as  an  organ  of  the  body.  It  is 
not  merely  a  chance  bounding  layer  of  the  organism,  but  truly  a  living 
organ  as  important  as  any  of  the  viscera.  Indeed,  few  organs  have  so 
many  functions  concerned  with  so  many  sorts  of  essential  animal  activity 

Again  we  must  refer  the  reader  to  the  text-books  of  gross  and  micro- 
scopic anatomy,  that  he  may  acquire  a  knowledge  of  the  structure  of  the 
skin  before  he  tries  to  understand  its  functions. 


Fig.  172 


The   functions  of  the  skin.      In  each  of  the  nine  portions  of  this  diaRram   tliere  is  represented 
tliose  dermal   structures  chiefly  concerned  in  tliat  function. 

The  Functions  of  the  Skin. — Among  the  many  uses  which  the  human 
skin  might  })c  said  by  an  ingenious  person  to  have,  nine  especially  may 
be  noted.  I'hese  are  of  various  degrees  of  importance  to  the  organism, 
and  only  the  first  four  or  five  are  es.sential  to  its  health.  These  nine 
uses  of  the  .skin,  if  we  are  to  denote  each  of  tiiem  l)y  some  one  common 
expression,  are  protection,  .sen.sation,  thermotaxis,  excretion  of  sweat, 
secretion  of  .sebum,  respiration,  ab.sorption,  coloration,  and  support  of 


THE  SKIN 


313 


Fig.  173 


the  nails  and  hairs.  If  it  were  reasonal)le  to  say  of  animal  functions 
altogether  composing  one  harmonious  whole  that  ''this  function  is 
more  important  than  that  one,"  we  might  consider  the  order  given  above 
as  perhaps  that  of  their  relative  consequence  to  the  organism.  (See  the 
diagram,  Fig.  172.) 

Protection  is  well  afforded  hv  the  skin  through  its  structure,  composi- 
tion, and  relations  to  the  bodily  parts  it  covers.  It  protects  from  physical 
and  chemical  stimuli  which  might  injure  the  organism  in  two  opposed 
directions — from  mild  stimuli  by  its  sense- 
organs  which  warn  the  nervous  system  of 
their  presence,  and  from  severer  stimuli 
by  the  horny  layer  which  it  exposes  to 
them.  It  is  with  the  latter  only  that  w^e 
are  just  now  concerned.  The  structure 
of  the  stratum  corneinn  is  peculiarly  well 
adapted  to  its  functions,  for  it  consists 
of  very  many  layers  of  dead  or  half  dead 
squames  or  scales  piled  up  in  multitudes 
on  each  other  but  firmly  connected  so 
that  they  form  a  membrane,  flexible,  ex- 
tensible, and  soft. 

Because  of  the  absence  of  nerves  from 
the  epidermis  it  has  no  sensibility  and 
the  individual  is  not  irritated  by  contact 
with  the  air,  water,  and  solid  bodies,  as 
he  would  be  did  the  nerves  ramify  in  the 
surface ;  of  course  life  under  the  latter  cir- 
cumstances is  almost  inconceivable.  The 
epidermal  scarf-skin  on  this  account  is 
an  ideal  bounding  surface  of  an  animal 
body. 

The  epidermis  because  of  its  ciiief 
chemical  component,  keratin  (an  albumi- 
noid), as  also  because  of  its  scaly  struc- 
ture, is  a  fine  non-conductor  of  heat.  It 
thus  shields  the  body  from  the  sun  to  an 
extent  and  from  excessive  artificial  heat. 
^Yhen  pigment   is  developed   in  the  skin 

(as  in  freckles,  in  "tanning"  from  sun-  and  wind-burn,  and  in  the  Xegro 
race),  it  is  biologically  supposed  to  be  deposited  as  a  still  further  protec- 
tion against  excessive  light  and  heat.  The  dead  keratin  of  the  skin's 
outer  layers  when  dry  is  also  a  non-conductor  of  electricity,  and  this  is 
a  matter  of  some  importance  because  of  the  electrical  developments  of 
recent  years. 

This  same  scaly  structure  makes  the  skin  a  relatively  poor  absorber 
of  everything,  as  good  protection  requires.  As  we  shall  see  before  long, 
only  fats  and  oils  enter  it  readily.     Xo  substance  passes  through  it,  how- 


.^"^m^ 


Vertical  section  of  the  epiderm  of 
the  hand's  palm.  X  100  diameters:  1, 
very  thick,  horny  layer,  composed  of 
superimposed  cells  without  their  nu- 
clei; 2,  mucous  layer  of  nucleated 
cells;  3,  upper  part  of  this  layer  sep- 
arated from  the  rest  by  a  wavy  line; 
4,  interpapillary  depressions;  5,  pap- 
illary recesses.      (Sappey.) 


314 


THE  SKIN 


ever,  with  anywhere  near  the  readiness  with  which  it  would  be  absorbed 
by  the  average  naked  body- tissues  served  with  an  abundance  of  lym- 
phatics and  of  capillaries.  "Water  finds  its  way  through  the  unctuous 
scaly  epidermis  only  in  minute  amounts,  this  waterproofing  of  the  skin 
being  produced  by  the  sebum,  a  fat  poured  out  into  the  hair-follicles 
and  on  the  surface  (see  below). 

The  skin  is  freely  movable  over  the  fatty  subcutaneous  tissues  and  is, 
moreover,  very  elastic.  These  two  properties  prevent  the  body's  injury 
by  contact  with  such  heavy  objects  as  press  and  move  at  the  same  time. 
In  these  cases  the  skin  glides  over  the  muscles,  etc.,  beneath  it  and  the 
surface  of  the  body  is  not  torn  or  bruised. 

Fig.  174 


The  lower  part  of  the  epidermis  of  the  hand-palm,  as  seen  in  schematic  section:  o,  layer  of 
cylinder  cells;  h,  basal  fibers;  c,  layer  of  cells  whose  fibers  extend  in  all  directions;  d,  layer  of 
cells  whose  fibers  are  parallel  to  the  skin's  surface;  e,  layer  of  cells  whose  fibers  are  beginning  to 
disappear  in  the  cytoplasm;  /,  stratum  granulosum;  g,  stratum  corneum  (a  small  part  of  it). 
(Kromayer.) 


The  two  parts  of  the  skin,  the  corium  and  epidermis,  are  both  very 
elastic,  the  former  by  virtue  of  its  network  of  elastic  fibers  and  the  latter 
because  of  its  scaly  structure,  which  allows  of  considerable  stretching.  It 
is  essential  that  the  covering  of  the  dilferent  parts  of  the  body  should  be 
extensible  to  a  large  degree,  because  many  temporary  conditions,  normal 
and  abnormal,  increase  the  size  of  local  portions  of  the  organism.  Thus 
when  the  biceps  of  the  arm  contracts  vigorously  the  arm  increases  much 
in  circumference  around  the  center  of  the  muscle.  In  pregnancy,  if  the 
skin  were  not  clastic  to  a  high  degree  it  would  be  torn  at  times.  Tumors 
superficially  placed  and  ascites  sometimes  show  a  like  need  for  dermal 
stretching. 

In  several  places  by  the  thickness  of  its  epidermis  the  skin  constitutes 
a  pari  wliich  prevents  frc(|uent  injury  to  the  parts  beneath  it,  for  example, 


THE  ^KIN  315 

over  the  gluteus  maximus  and  on  parts  of  the  palm  of  the  hand.  The 
subcutaneous  fat  helps  in  this  matter.  Under  the  heel  the  skin  is  very 
thick,  especially  the  fat  and  the  epidermis,  and  constitutes  a  cushion  to 
relieve  the  jarring  of  the  spine  which  else  would  occur,  and  with  injurious 
effect,  in  walking.  As  is  familiarly  seen  in  the  causation  of  corns  and  of 
calluses,  especially  on  the  hands,  continued  or  oft-repeated  pressure  on 
a  portion  of  the  skin  gradually  causes  a  thickening  of  the  epidermis. 
By  this  principle  active  manual  occupations  and  sports  soon  lead  to  the 
development  of  defences  to  abrasion  and  inflammation  at  just  the  spots 
where  they  are  needed. 

In  cases  of  injury  to  the  external  parts  of  the  body  which  are  much 
in  contact,  especially  the  fingers  and  the  toes,  the  presence  of  the  dead 
epidermis  not  liable  to  inflammation  prevents  the  injured  parts  from 
growing  together  before  they  come  into  use  again. 

Because  of  its  structure  and  the  materials  from  which  it  is  made,  the 
skin  is  flexible  and  soft  yet  resistant  to  all  but  incisive  blows.  It  has  in 
short  in  a  lesser  degree  the  well-known  and  unique  properties  of  leather, 
which  of  course  is  skin  killed,  hardened,  and  preserved. 

Besides  these  physical  agencies  there  are  many  solid,  licjuid,  and 
gaseous  chemical  substances  which  come  in  contact  with  the  skin 
occasionally.  The  epidermis,  however,  especially  the  superficial  parts 
of  it,  is  little  more  than  a  complicated  network  of  keratin,  which  is  one 
of  the  most  insoluble  substances  entering  into  the  organism.  It  is  un- 
affected by  most  of  the  things  which  in  a  state  of  nature  are  apt  to  come 
in  contact  with  it.  Many  of  these  (for  example,  the  alcohols)  would 
injure  seriously  the  average  living  tissues,  and  alkalies  and  strong  acids 
attack  it  still  more  readily.  In  general,  however,  it  is  a  very  resistant 
material  and  therefore  one  excellently  adapted  to  intervene  between  an 
organism  and  its  varied  environment.  (See  further  as  to  the  chemical 
status  of  the  albuminoids  in  the  chapters  on  protoplasm,  food,  and 
nutrition.)     (Fig.  173.) 

Light  is  one  of  the  agencies,  chemiphysical  in  action,  against  too  much 
of  which  the  pigment-cells  of  the  epidermis  protect  the  body-tissues. 

In  addition  to  furnishing  protection  to  a  degree  against  physical  and 
chemical  adversaries  of  its  organism,  the  integument  is  a  defence  against 
parasites,  including  the  pathogenic  bacteria  except  such  as  dwell  within 
its  tissues.  As  long  as  the  uncracked  epidermis  only  is  presented  to 
bacteria  there  is  relatively  little  danger  of  infection,  for  its  mass  of  minute 
dead  scales  admirably  serves  as  a  filter  against  their  passage,  much  as 
does  cotton  in  the  bacteriological  laboratory.  Contrast  with  this  the 
prompt  and  vigorous  invasion  of  mucous  membranes  by  germs  of  disease. 
These  former  do  not  have  the  dry,  cool,  filtering  mass  of  scales  which 
make  up  the  epidermis,  but  are  living  tissues  rich  in  most  of  the  conditions 
the  development  of  microorganisms  requires,  such  as  moisture,  warmth, 
and  nutriment. 

The  continual  exfoliation  of  the  dead  epidermal  squames  protects  the 
body  largely  from  the  growth  of  parasites  such  as  one  sees  sometimes  on 


316 


THE  SKIN 


the  shells  of  molluscs  and  the  carapaces  of  turtles.  The  many  parasitic 
diseases  of  the  skin  which  are  found,  such  as  scabies,  tricophytosis,  etc., 
are  due  to  rapidly  growing  organisms,  and  are  liable  to  occur  especially 
on  skins  in  w'hich,  through  infrequency  of  bathing  (which  is  essentially 
maceration  followed  by  exfoliation)  the  outer  layers  of  the  epidermis 
remain  untluly  long  exposed  to  the  environment. 

Sensation  or  sensitivity  is  perhaps  the  next  most  important  function 
of  the  human  skin.  If  the  term  protection  be  used  in  a  broad  sense, 
much  of  the  usefulness  of  the  skin's  sensitivity  would  come  under  it. 


Fig.  175 


cM 


cM 


za — 
OK— 


-cP 


. it 


Half-schematic  section  of  the  i^kin  on  the  V)ali  of  the  finder  to  show  the  locations  of  the  sense- 
orntans:  Sp,  layer  of  papilhe;  ,SV,  reticular  layer;  ON,  Huffini  corpuscles;  SI,  nerve-trunk;  la, 
fat  globulesi;  cM ,  Meis.sner  corpuscle;  cP,  Vater-Paciiiian  coriMiscle;  as,  sweat-gland;  ^K,  artery. 
Gold-chloride.      (Rauber.) 

One  of  the  chief  functions  of  the  dermal  sense-organs  is  to  warn  tlie 
animal  within  of  external  injurious  conditions  such  as  heat,  cokl,  and 
various  sorts  of  contact  with  foreign  l)()dics.  Because  the  sense-organs 
have  functions  other  than  protection,  however,  we  consider  them  as 
having  uses  of  their  own.  The  description  of  these  afferent  end-organs 
and  of  their  functions  is  given  in  a  later  chapter  (page  351,  etc.),  so  that 
here  we  need  only  mention  sonif  of  the  general  con(h'tIons  of  their  activity. 
One  of  the  most  liasal  of  biological  principles  is  that  of  the  unity  of 


THE  SKIN  317 

the  living  world  :  each  part  is  more  or  less  dependent  on  every  other  part. 
Further  than  this  every  animal  is  at  once  the  product  of  and  dependent 
on  its  environment  of  natural  energies  and  materials.  By  way  of  the 
stomach  and  the  lungs  these  in  great  numbers  enter  more  or  less 
into  the  animal's  metabolism  or  afi'ect  it  in  many  ways  through  its 
nervous  systems.  Some  of  these  latter  influences  enter  by  way  of  the 
sense-organs  of  the  skin. 

There  are  numerous  minute  "spots"  in  the  skin  sensitive  to  pressure 
(touch),  pain,  heat,  and  cold,  respectively,  and  it  is  not  difficult  to  stimu- 
late these  various  points  in  such  a  way  as  to  produce  pure  sensations  of 
at  least  these  four  kinds.  (See  below,  page  366,  where  some  details  are 
given.)  ^Yhen,  for  example,  a  touch-organ  is  stimulated  separately, 
nothing  whatever  but  a  sensation  of  touch  is  experienced,  no  pain  or 
cold  or  warmth.  "When  a  "pain-spot"  is  properly  excited  only  pain  is 
experienced^ — no  suggestion  of  touch  or  of  cold  or  of  warmth.  Besides 
the  definite  end-organs,  there  seem  to  be  everywhere  fibrils  of  nerve- 
tissue.  Especially  is  this  the  case  among  the  epithelial  cells  of  the 
epidermis  and  of  the  mucous  membranes,  and  in  the  cylinders  of  tissue 
encasing  the  lower  ends  of  the  almost  universally  distributed  hairs. 
IMechanical  irritation  of  these  fibers  or  fibrils  starts  impulses  in  their 
afferent  nerves,  but  how  these  differ  in  their  mode  of  sensation-making 
from  those  set  going  from  the  various  touch-corpuscles,  etc.,  is  at 
present  not  understood. 

The  consideral)le  variety  and  immense  number  of  the  skin's  sense- 
organs  are  the  facts  to  be  noted  here.  By  them  this  organ  is  made 
practically  a  perfect  coupler  between  the  animal  and  its  physical  environ- 
ment. 

Thermotaxis,  the  regulation  to  body- temperature,  is  one  of  the  im- 
portant functions  of  the  integument.  By  the  reflex  or  voluntary  action 
of  various  and  certain  elements  within  the  skin's  thickness,  combined 
with  the  nervous  system,  the  temperature  is  kept  within  the  limits  with 
which  we  are  familiar,  namely,  one  or  two  degrees  above  or  below 
37°  centigrade.  We  have  already  discussed  the  methods  of  heat- 
production  and  of  heat-loss  and  have  seen  that  the  arrangements  for 
heat-regulation  involve  nearly  all  parts  of  the  body.  Of  the  organs  thus 
concerned,  none,  it  will  be  recalled,  is  more  important  than  the  skin. 
From  it  the  very  large  part  of  the  heat  lost  from  the  body  is  radiated  or 
conducted.  As  we  have  seen,  the  proportional  area  of  the  skin  to  the 
metabolic  tissue-mass  producing  heat  within  it  is  a  chief  factor  in  the 
conduct  of  thermolysis.  Again,  it  is  the  skin  which  secretes  the  sweat, 
by  whose  evaporation  largely  the  heat  is  lost  from  the  body. 

The  Sweat. — Another  function  of  the  human  skin,  but  partly  involving 
the  preceding,  is  the  excretion  of  sweat.  This  substance  is  a  liquid 
of  very  low  specific  gravity  produced  by  certain  closely  coiled  glands 
lying  in  the  subcutaneous  layer  of  tissue.  Their  product,  however, 
is  poured  out  on  the  skin's  surface.  Sweat  is  termed  an  "excretion" 
because  it  is  waste  matter.     It  is,  however,  of  great  use  to  the  organism 


318 


THE  SKIN 


as  it  passes  away  from  it.  It  is  only  because  of  its  location  on  the  body- 
surface  that  the  skin  rather  than  some  internal  organ  excretes  the  sweat, 
for  it  passes  off  largely  by  evaporation,  for  the  purpose  just  considered 
above. 

The  purely  excretory  aspects  of  the  sweat  have  been  briefly  treated  of 
especially  in  the  chapter  on  Nutrition  (see  page  252).  We  have  now  to 
describe  its  composition,  mode  of  production,  and  relations  to  the  skin 
and  to  thermotaxis  rather  than  to  the  removal  of  waste  from  the  body. 
First,  a  few  words  as  to  its  physical  and  chemical  nature. 

Hiunan  sweat  is  a  somewhat  opalescent  colorless  liquid  with  a  specific 
gravity  varying  between  1003  and  1010  according  to  the  conditions  under 
which  it  is  produced,  but  averaging  perhaps  1005;  it  is,  then,  one  of  the 
most  watery  of  the  body-liquids.  Three  samples  analyzed  by  Camerer 
had  an  average  of  98.5  per  cent,  of  water  and  1.5  per  cent,  of  "solids:" 


Fig.  176 


A  human  sweat-gland:    a,  the  knot  of  the  gland  surrounded  by  veinleta;   b,  excretory  duct; 
c,  basket-like  capillary  network  about  the  gland.      (Todd-Bowman.) 

three-quarters  of  the  ash  was  sodium  chloride.  In  reaction  sweat 
appears  to  be  either  alkaline  or  (later)  acid,  depending  on  the  time  it 
has  been  in  contact  with  the  epidermis.  Camerer  found  the  sweat 
poured  out  in  a  liot-air  l)ath  to  be  acid,  that  in  the  more  sudorific  vapor- 
l)ath,  alkaline.  There  is  some  evidence  that  what  one  might  call  mus- 
cular-katabolic  sweat  tends  to  be  more  acid  than  that  excreted  by  the 
glands  during  bodily  rest,  the  more  profuse  the  sweat  the  greater  its 
liability  to  be  neutral  or  alkaline.  There  are  present  small  proportions 
of  neutral  fats,  urea,  in"ic  acid,  aromatic  oxy-acids,  sulphates  of  phenol, 
skatol,  etc.,  kreatinin,  formic  and  acetic  acids,  and  traces  of  proteid 
(especially  in  alkaline  sweat).  Altogether  about  0.15  per  cent,  of  nitrogen 
are  present,  most  of  which  are  in  the  urea  and  uric  acid.  The  universally 
excreted  cholesterin  does  not  fail  to  be  present.     There  are  contained 


THE  SKIN  319 

also  at  all  times  traces  of  sulphocvankles,  and  it  is  these,  perhaps,  in 
combination  with  proteid  decomposition-products  of  unknown  nature, 
that  make  the  sweat  toxic  when  ingested.  The  odor  of  sweat,  especially 
if  old,  varies  with  the  volatile  fatty  acids  excreted  at  that  place,  for  the 
latter  difier  somewhat  in  various  localities.  The  sodium  chloride  present 
gives  sweat  a  salty  taste.  Under  the  microscope  sweat  is  seen  to  contain 
epidermal  debris  and  an  occasional  waste-product  from  the  tissues  in 
and  about  the  sweat-glands.  The  urea  present  at  all  times  more  or  less 
may  be  of  great  importance  during  incapacitating  disease  of  the  kidneys. 
Ordinarily  it  constitutes  about  one  part  in  a  thousand  of  sweat,  but  when 
the  excretion  of  urine  is  suppressed  it  may  be  in  cjuantity  sufficient  to  be 
seen  in  crystals  on  the  skin,  and  to  materially  aid  in  the  life-saving  excre- 
tion of  nitrogen. 

The  nervous  system  superintends  the  secretion  of  sweat.  Its  influ- 
ences pass  out  in  the  neuraxones  of  the  sympathetic  by  way  of  the  anterior 
roots  of  the  cord.  Centrally  the  fibers  of  the  sweat-nerves  probably  pass 
upward  in  the  cord  to  a  center  or  centers  in  the  medulla  probably,  but 
as  yet  not  exactly  located.  Function  indicates  their  very  close  relation 
both  with  the  vasomotor  and  with  the  thermogenic  centers.  The  uni- 
lateral sweating  seen  occasionally  in  nerve-clinics  suggests  very  strongly 
that  there  is  a  center  on  each  side  of  the  medulla. 

Sweat  is  excreted  continually  and  when  in  quantities  too  small  to  be 
seen  on  the  skin  is  termed  invisible  or  "insensible"  sweat.  Its  quantity 
is  continually  changing  as  the  regulation  of  body-heat  requires,  but  may 
average  1500  c.c.  daily.  Under  certain  normal  conditions,  all  of  which 
involve  an  increase  of  body-katabolism  or  at  least  of  body-heat,  the  sweat 
is  so  much  augmented  that  it  is  no  longer  evaporated  as  fast  as  excreted, 
and  it  then  collects  on  the  surface.  It  is  then  termed  "sensible"  or 
visible  perspiration.  As  we  have  seen,  these  two  sorts  may  differ  some- 
what in  composition,  but  not  much;  the  more  abundant  the  sweat, 
however,  the  larger  the  proportion  of  water  and  the  more  likely  it  is  to  be 
alkaline  instead  of  acid.  Besides  the  normal  conditions  mentioned 
below,  sweat  may  be  augmented  by  pathological  causes  not  involving 
metabolism,  for  example  certain  drugs  (as  pilocarpine  and  nicotine),  and 
by  some  sort  of  derangement  of  the  sympathetic  sweat-nerves  or  -centers 
in  certain  nervous  diseases.  This  is  called  by  dermatologists  a  condition 
of  hyperidrosis.  Its  etiology  is  often  obscure,  but  is  usually  some 
derangement  of  the  sympathetic. 

Among  the  physiological  conditions  determining  an  increase  of  sweat  are 
these  six:  An  increase  in  the  temperature  of  the  blood;  vaso-dilatation  in 
the  skin;  a  high  external  temperature;  an  increase  in  the  proportion  of 
Water  in  the  blood  (hydremia);  venosity  of  the  blood;  and  direct  cerebral 
stimulation  of  the  sweat-centers  in  emotional  conditions,  for  example 
fear.  Physical  and  even  mental  exercise  (the  former  being  perhaps  the 
most  common  cause  of  the  appearance  of  sweat  on  the  skin)  produce  the 
effect  by  heating  the  blood  thus  stimidating  the  centers  and  perhaps 
also  the  glands  directly,  at  the  same  time  causing  peripheral  vaso-dila- 


320 


THE  SKIX 


tation  which  in  turn  increases  the  flow  of  sweat.  The  enlarged  amount 
of  proteid-kataboHsm  in  muscular  exercise  has  little  to  do  with  the 
increase  of  the  sweat,  for  the  kidneys  are  the  glands  arranged  to  take 
these  nitrogenous  excreta  from  the  blood.  The  excretion  of  the  water 
produced,  however,  is  shared  between  the  two.  It  is  only  when  the 
epithelium  of  the  kidneys  is  thrown  out  of  action  or  destroyed  (as  in 
Bright's  disease)  that  the  sweat-glands  vicariously  take  on  the  excre- 
tion of  considerable  amounts  of  nitrogen  in  urea,  this  then  soon  degen- 
erating to  ammonia. 


Fig.  177 

AiOff£ 

LESS 

SWEAT 

WATER. 

SWEOT 

Merenf 
Aferve 


Efferent 


Afferent 
Nerve 


Efferenf 
Nerve 


VA50-D/LAT/0/\f 


INCPt.  METAB 
HEAT 
EMOTION 
DRUQ5 


VA50-  CO/^STK/CT/OAf 


Mechanism  of  .^weat-secretion'.'  On  the  left  side  of  the  picture  are  represented  the  mechanism 
and  some  of  tlie  conditions  of  an  increased  production  of  sweat,  and  on  the  right  side  those  of  less 
sweat.      In  the  middle  is  a  diagrammatic  sweat-gland  delivering  its  jjroduct  into  the  epidermis, 

A  high  temperature  of  the  skin's  environment  stimulates  the  flow  of 
sweat  reflexly,  and  probal)ly  through  the  agency  of  the  minute  auto- 
matic thermostats  (heat-corpuscles)  scattered  throughout  the  integu- 
ment. (See  Chapter  X.)  Sweat  runs  by  the  liter  fr(Hn  the  workmen  in 
foundries,  glass-works,  and  rolling-mills,  for  they  sometimes  work  in 
temperatures  which  would  be  pr()m})tly  fatal  were  the  air  very  moist 
instead  of  dry  and  were  the  skin  dcjjrived  of  its  active  sweating  by  any 
othercau.se.  PLxce.ssive  heat,  internal  or  external,  as  well  as  cold,  checks 
the  secretion,  and  by  methods  the  reader  can  doubtless  readily  explain. 

Of  the  six  conditions  mentioned  as  more  or  less  normal  states  showing 
an  increase  of  sweat-secretion,  five  most  likely  act  largely  or  wholly  on 


THE  SKIN  321 

the  centers  in  the  nieduUa  and  the  cord.  The  least  normal,  a  watery 
state  of  the  blood,  probably  produces  its  effect  directly  on  the  epithelium 
of  the  sweat-fflands,  much  as  does  the  same  sort  of  action  in  the  kidnevs. 
In  just  what  manner  the  presence  of  too  much  carbon  dioxide  in  the  blood 
works  is  not  at  present  understood.  Many  sorts  of  reflex  stimulation  of 
the  spinal  cord  and  brain  cause  an  increased  flow  of  sweat,  whether  the 
stimuli  come  from  the  sensory  nerves  or  from  deeply  lying  parts  of  the 
brain  such  as  the  optic  thalami,  the  centers  of  emotional  expression. 
The  sweat-glands  are  not  readily  stimulated  directly  by  warming  the 
skin  containing  them,  but  easily  and  from  many  ditt'erent  directions  by 
first  stimulating  the  controlling  centers  in  the  central  nervous  system. 

We  have  already  considered  above  in  two  difl'erent  places  the  two 
general  functions  of  the  sweat,  namely,  to  excrete  water  (and  many  other 
things  in  small  amounts)  and,  largely  by  this  latter  means,  to  regulate  the 
loss  of  body-heat.  These  statements  need  not  be  renewed  here.  As  a 
means  of  excreting  water  from  the  organism  the  sweat-glands  seem  to  be 
just  about  on  a  parity  with  the  kidneys.  As  regulator  of  heat-loss  the 
sweat  is  paramount. 

The  Secretion  of  Sebum  is  a  dermal  function  more  or  less  closely 
concerned  in  the  skin's  protection  of  the  body.  Because  largely  useful, 
sebum  is  classed  as  a  secretion  rather  than  as  an  excretion.  Sebum  is 
of  many  difterent  varieties  according  to  its  precise  function  on  different 
parts  of  the  body.  It  varies  in  the  hair-follicles,  in  the  external  auditory 
meatus,  on  the  edges  of  the  eye-lids,  on  the  lips  and  in  corners  of  the 
mouth,  in  the  cervix,  corona  glandis,  foreskin,  labia  minora,  etc.  Vernix 
caseosa,  the  sebum  covering  the  body  at  birth,  is  still  unlike  all  the  others. 

Wherever  it  occurs,  the  essence  of  sebum's  composition  is  fat,  largely 
olein  and  palmitin.  These  make  the  excretion  liquid  when  secreted 
and  allow  it  to  harden  more  or  less  on  exposure  to  the  cool  air.  Soaps 
are  present  in  considerable  proportion,  and  glycerin,  and  a  casein-like 
nucleo-proteid.  It  contains  earthy  and  alkaline  phosphates  and  chlorides 
of  sodium  and  potassium.  Cholesterin  is  always  to  be  found.  In 
appearance  also  sebum  varies  largely  with  the  place  where  it  is  secreted ; 
so  does  its  odor  as  well,  smegma,  for  example,  having  in  the  brutes  an 
odor  with  much  biological  value. 

The  sebaceous  glands  are  attached  to  the  follicles  of  the  hairs  and  pour 
their  product  into  them,  whence  it  is  distributed  throughout  the  epidermis 
by  the  movements  of  the  skin.  Just  within  the  hair-sheath  is  the  mem- 
brana  propria,  continuous  with  a  similar  layer  in  the  follicle.  Within 
this  in  turn  are  several  strata  of  gland-cells  proper,  the  outer  two  or  three 
being  like  those  of  the  external  root-sheath  of  the  hairs.  The  inner 
strata  of  epithelial  cells  are  difl'erent,  containing  fat-globules  in  quantities 
sufficient  to  give  the  cytoplasm  a  reticulated  appearance,  while  the  nuclei 
are  compressed.  These  fat-globules  constitute  the  product  of  the 
secretion,  for  the  innermost  cells  containing  them  are  continually  break- 
ing down  in  a  mass,  thus  becoming  sebum.  These  are  as  continually 
replaced  by  the  basilar  cells  below  them,  which  in  turn  develop  sebum- 
21 


322  THE  SKIN 

granules  and  press  toward  the  lumen  of  the  alveoli.  This  process  is  in 
essential  respects  like  that  of  the  goblet-cells  secreting  mucin.  Some- 
times the  cell  does  not  go  to  pieces  in  situ  but  only  after  being  extruded 
from  the  gland.  The  excretory  ducts  are  wide  and  ordinarily  empty 
into  the  upper  third  of  the  hair-follicle;  their  walls  also  secrete  sebum. 

The  functions  of  sebum  are  not  hard  to  understand  when  its  general 
fatty,  emollient  nature  and  the  place  of  its  excretion  are  kept  in  mind. 
It  is  essentially  and  primarily  an  oily  softener  of  the  epidermis  and  of  the 
hairs  found  nearly  everA^vhere  over  the  body.  Without  it  the  epidermal 
scales  and  the  scaly  hair  would  become  hard  and  brittle-  and  unjfit  to 
perform  their  protective  functions.  One  of  the  most  common  features 
of  the  body's  environment  is  water  or  watery  vapor.  The  fat  which 
the  sebum  supplies  to  the  epidermis  serves  to  make  the  latter  tough  and 
impervious  to  water,  which  else  sometimes  would  be  absorbed  by  the 
capillaries  and  derange  the  organism  more  or  less.  The  hairs  especially 
are  dependent  on  an  abundance  of  oil  for  their  normal  suppleness  and 
strength.  In  general  over  the  body  then  the  sebum  keeps  the  skin's 
outer  layer  soft  and  pliable,  and  prevents  the  maceration  of  the  epidermis 
which  water  would  else  be  sure  to  cause.  There  are  no  sebaceous 
glands  on  the  palms  of  the  hands  or  on  the  soles  of  the  feet,  nor  in  two 
or  three  other  narrow  localities. 

In  special  locations,  mostly  mentioned  above,  the  sebum  has  special 
functions  in  addition  to  its  general  uses  just  described :  In  the  eyeUds,  the 
secretion  of  the  sebaceous  (Meibomian)  glands  has  the  function  of  pre- 
venting the  cohesion  of  the  lids  when  they  are  closed,  as  during  sleep. 
One  sees  its  use  in  conjunctivitis  of  various  sorts,  for  then  the  secretory 
process  is  often  exaggerated  and  the  lids  cannot  be  opened  in  the  morning 
until  the  adhesive  sebum  is  softened  and  removed. 

In  the  inner  part  of  the  external  ear,  the  external  meatus,  the  sebum  is 
termed  cerumen  or  ear-wax.  There  it  lubricates  the  membrana.  It 
serves  also  the  purpose  of  partly  preventing  the  entrance  of  insects  and 
even  of  small  particles  of  lifeless  foreign  matter,  the  stiff  hairs  also  often 
present  aiding  in  this.  For  the  purpose  of  making  the  cavity  still  more 
inhospitable  to  insects,  the  cerumen  has  an  intensely  bitter  taste,  thus 
the  better  preventing  small  insects  from  coming  in  contact  with  the 
membrana  tympani. 

On  the  lips  and  corners  of  the  mouth  the  sebum  is  necessary  to  prevent 
the  cracking  of  the  integument,  for  these  are  places  where  the  skin  is 
thin  and  liable  to  be  broken  or  slightly  torn. 

The  vernix  caseosa  which  covers  the  infant  at  birth  is  evidently  a 
lubricant  facilitating  the  passage  outward  of  the  child  and  preventing 
abrasion  both  of  the  latter's  very  delicate  skin  and  of  the  birth-canal  of 
the  mother.  Pigeons'  milk  is  a  form  of  sebinii  on  which  the  young  birds 
are  fed  at  first;  it  comes  from  temporary  sebaceous  glands  developed  in 
the  crops  of  both  parents.  The  sebum  of  sheep  is  called  lanolin,  and 
serves  to  keep  the  wool  soft,  pliable,  and  water-proof.  When  the  amount 
of  the  sebum  is  generally  excessive  in  quantity  the  condition  is  known 


THE  SKIN  323 

in  (leniuitology  as  sel)orrhea  and  popularly  as  dandruH'.  Sometimes 
the  secretory  product  is  along  with  its  over-abundance  abnormally  oily 
(seborrhea  oleosa),  while  at  other  anrl  more  frecjuent  times  the  excessive 
sebum  is  thicker  in  consistence  than  usual  (seborrhea  sicca).  The  cause 
of  this  hyper-secretion  is  not  known,  but  it  seems  to  be  related  to  some 
lowered  tone  of  the  nervous  system  or  the  blood.  It  is  most  abundant 
in  those  regions  where  the  sebaceous  glands  are  most  common. 

Respiration  is  another  subsidiary  function  of  the  skin.  It  appears 
that  under  normal  conditions  about  one-half  of  one  per  cent,  of  the  Ijody's 
total  respiration  is  carried  on  directly  through  the  epidermis.  When  the 
lungs  are  thrown  out  of  function  in  large  part  the  respiratory  action  of  the 
skin  may  be  largely  increased,  although  not  to  an  extent  which  makes 
it  ever  life-saving  to  the  human  organism.  The  subject  has  already 
been  discussed  in  the  chapter  on  respiration  (see  page  129). 

Absorption  of  certain  substances  through  the  skin  takes  place  under 
the  necessary  conditions.  The  process  is  more  important  therapeuti- 
cally, by  artificial  means,  than  as  a  spontaneous  physiological  process. 
It  is  not  apparent  that  naturally  any  su})stance  save  perhaps  oxygen  in 
very  small  amounts  passes  inward  through  the  intact  epidermis,  so 
perfect  is  the  protective  structure  and  function  of  the  integument. 

When  the  body  is  immersed  in  water,  especially  if  the  latter  be  warm, 
it  is  likely  that  a  very  small  amount  finds  its  way  into  the  circulation. 
Thus,  ship-^^Tecked  persons  have  often  relieved  themselves,  somewhat, 
of  the  feeling  of  diirst  by  immersing  their  bodies  even  in  the  salty  ocean- 
water.  This,  however,  is  no  proof  that  any  valuable  amount  of  the 
water  enters  the  body,  for  in  the  first  place,  no  one  has  ever  saved  him- 
self from  <lying  of  thirst  (that  is  from  loss  of  water  from  the  blood  and 
body-tissues)  by  thus  surrounding  the  body  with  water.  This  loss  of 
water  normally  occurs  half  at  least  by  evaporation  from  the  skin,  and 
immersion  in  water  would  check  this  evaporation  and  so  give  relief  to 
some  extent. 

The  sort  of  substances  which  may  be  made  artificially  to  pass  into  and 
through  the  normal  skin  (including  the  epidermis)  are  mostly  such  as 
are  already  there,  namely  fats.  These  even  when  only  placed  upon  the 
epidermis  are  absorbed,  and  unlimited  amounts  may  be  made  to  pass 
inward  by  inunction.  Naturally  also  substances  soluble  in  fats  likewise 
readilv  enter  the  organism.  This  fact  is  taken  advantao:e  of  in  medi- 
eating  not  only  the  skin  itself,  but  the  entire  organism.  Thus,  a  person 
is  readily  salivated  by  the  inunction  of  mercurial  ointments.  Similarly, 
alcoholic  extracts  and  ethereal  solutions,  being  soluble  in  the  sebum  and 
body-fats,  may  be  readily  made  to  enter  the  unbroken  skin. 

It  is  the  oiled  epidermis  which  prevents  the  passage  inward  of  most 
substances,  for  the  mucous  membranes  and  the  naked  tissue-protoplasm 
readily  absorb  a  large  variety  of  materials.  The  subject  of  absorption 
through  the  skin  has  not  nearly  the  importance  or  popularit}'  now  that  it 
had  formerly  when  it  was  supposed  by  many  that  the  organism  received 
much  benefit  by  absorbing  the  substances,  for  example,  dissolved  in 


324 


THE  SKIN 


various  sorts  of  natural  springs.  The  benefits  from  such  bathing  is 
now  known  to  be  much  more  indirect:  hygienic  and  mental  rather  than 
chemical. 


Fig.  178 


Xnrleiis 


Pigment-cell  from  a  j^oung  salamander's  skin,      ""^"/i-      (Szymonowicz  and  MacCallum.) 

Fig.  179 


V.  \ 


^   V) 

I 

Pigment  cells  from  the  .'-kin  of  the  frog:    /,  extended;    //,  and  ///,  degrees  of  contraction; 
IV,  wholly  contracted.      (Verworn.; 

Coloration. — "^riiis  dermal  function  is  served  by  pigment-cells  of  various 
colors  and  in  many  various  locations  on  the  body's  surface.  We  need 
not  discu.ss  the  chemistry  of  the  difi'erent  pigments  found  in  protoplasm, 
for  the  coloring-matters  are  complex,  and  besides  their  relation  to  the 
tissue-metabolism  is  not  vet  well  understood. 


THE  SKIN 


325 


The  pigments  are  the  secretory  products  of  certain  cells  of  the  connec- 
tive-tissue class,  but  differentiated  further  for  this  special  purpose.  In 
some  of  the  "lower"  animals  these  cells  have  distinct  ameboid  retraction- 
and-expansion  movements  described  somewhat  in  the  chapter  on  Proto- 
plasm. A  tendency  to  this  perhaps  is  seen  in  the  going  and  coming  of 
freckles  and  tan  and  especially  in  the  quick   blanching  of   the  hair  of 


Fig.  180 


Hair-follicle  showing  its  unstriated  muscles  and  the  sebaceous  gland:  1,  the  hair-root;  2,  its 
bulb  embracing  the  papilla  of  the  hair-follicle;  3,  internal  sheath  of  the  root,  and  4,  external 
sheath;  5,  tunic  of  transverse  fibers  of  the  follicle;  6,  tunic  of  longitudinal  fibers;  7,  unstriated 
muscles  inserted  in  the  latter  layer;  8,  their  free  ends,  losing  themselves  in  the  superficial 
strata  of  the  skin;  9,  multilobular  sebaceous  gland;  10,  excretory  duct  of  same;  11,  simple 
sebaceous  gland;    12,  mouth  of  the  hair-follicle.      (Sappey.) 


the  head  (e.  g.,  Henry  ]\I.  Stanley  in  the  African  forest  of  the  Pigmies) 
under  the  emotion  of  terror  or  from  the  more  chronic  emotional  condition 
of  worry  and  trouble. 

At  least  two  biological  functions  are  served  by  surface-pigmentation 
in  man,  namely,  to  make  the  botly  more  beautiful  and  to  protect  its 
protoplasm  from  excessive  sun-light. 

Biologically  the  former  function,  that  of  ornamenting  the  body,  is  a 


326  THE  SKIN 

secondary  sexual  adaptation.  It  is  intended  to  make  the  sexes  mutually 
more  attractive,  and  this  tends  to  draw  them  together  reproductive ly. 
But  human  beauty  has  other  reasons  for  existence  than  this,  is  indeed 
"its  own  excuse  for  being."  To  this  virtue  the  various  pigments  of  the 
skin  and  its  appendages,  especially  the  hair,  distinctly  minister,  for  they 
help  materialh'  to  increase  the  beauty  of  the  human  form. 

As  protectors  of  the  sensitive  body-protoplasm  from  excessive  sun- 
light the  status  of  the  pigmentation  is  more  in  doubt.  It  is  not  easy  in 
particular  tc  decide  whether  the  secretion  of  brown  or  black  pigment 
which  occurs  after  long  exposure  to  bright  sunlight  is  a  sort  of  degenera- 
tive reaction  or  a  protective  process.  In  the  iris  it  has  evidently  the 
latter  function;  in  the  hair  of  the  scalp  blackness,  on  the  other  hand, 
would  tend  to  make  the  brain  warmer  than  were  the  hairs  white.  Orna- 
mental pigmentation  tends  to  occur  on  the  body  in  places  not  especially 
exposed  to  light,  for  example  on  the  scrotum. 

In  general  the  whole  subject  of  dermal  pigmentation  needs  more  careful 
working-out  in  its  chemical  as  well  as  its  histological  aspects. 

The  Hairs  and  the  Nails  are  properly  parts  of  the  skin  or  appendages  to  it. 

Hairs  are  found  nearly  all  over  the  body,  the  palms  and  soles  being 
marked  exceptions.  In  various  places  the  hairs  differ  greatly  in  size  and 
rigidity.  In  its  adult  stage,  the  hair  consists  of  medulla,  cortical  fibers, 
and  cuticle.  The  pigment-granules  are  scattered  in  the  cortical  layer. 
An  inner  and  an  outer-root  sheath  surround  the  growing  hair,  the  latter 
being  an  invagination  from  part  of  the  epidermis.  In  the  center  of  the 
base  of  the  hair  when  in  the  follicle  is  the  very  vascular  papilla.  Attached 
to  each  follicle  is  a  bundle  of  smooth  muscle-fibers  so  placed  that  its 
contraction  pulls  the  hair  into  an  erect  position,  as  happens  in  terror. 
Each  follicle  receives  one  nerve-fiber  which  enters  the  former  just  below 
the  duct  of  the  sebaceous  gland.  Here  it  divides  into  two  non-medullated 
fibers  which  surround  the  hair-follicle  and  from  this  partial  or  complete 
ring  many  varicose  fibers  extend  upward  and  terminate  outside  the  so- 
called  glassy  layer,  in  some  of  the  brutes  in  special  end-organs  (Retzius). 
The  muscles  of  the  hairs  are  supplied  from  the  gray  rami  communi- 
cantes  of  the  sympathetic  (Hu})er). 

From  what  we  know  of  the  structure  and  the  nature  of  the  hairs  three 
functions  at  least  may  be  noted:  protection  in  various  ways,  especially 
from  cold  and  heat;  as  sense-organs  of  touch;  and  ornamentation. 

The  nails  scarcely  need  discussion.  They  are  keratinous  coverings 
of  the  ends  of  the  fingers  and  toes,  extending  from  the  epidermis  and 
continually  pushing  out  at  a  slow  rate  by  growth  at  their  matrix.  They 
serve  to  protect  the  ends  of  the  fingers  and  toes  from  injury  and  render 
these  organs,  especially  the  latter,  useful  for  many  purposes  which  else 
they  could  not  serve. 


CHAPTER   X. 

THE    SENSES. 

We  have  already  learned  that  one  of  the  chief  functions  of  the  nervous 
system  is  to  correlate  the  parts  of  the  organism  into  a  unity,  and  the 
organism  as  a  whole  with  its  varied  and  changeful  environment.  The 
animal  is  no  independent  entity,  but  rather  part  and  parcel  of  its  environ- 
ment to  an  extent  not  often  realized.  Just  as  the  whole  animal  has  an 
environment  scarcely  ever  twice  alike,  so  also  has  each  of  the  organism's 
parts,  large  or  small.  It  is  the  main  function  then  of  the  sense-organs, 
so  called,  to  help  this  double  adaptation.  The  sense-organs  are  the 
peripherally  terminal  portions  of  the  afferent  nervous  system,  the  means 
by  which  the  latter  connects  itself  with  its  local  environment.  Homol- 
ogous to  the  sense-organs  at  the  periphery  of  the  afferent  nerves  are  the 
muscles  and  the  glands  at  the  periphery  of  the  efferent  set  of  nerves. 
The  former  receive  for  transmission  the  messages  from  the  "environ- 
ment" as  already  defined;  the  latter  perform  in  the  environment,  within  or 
without  the  organism,  the  bidding  of  the  animal's  will  whether  "reflexly" 
or  "voluntarily"  performed.  All  of  these  from  one  point  of  view  are  but 
parts  of  the  nervous  system;  functionally,  however,  every  bodily  part  is 
sovereign  and  none  the  servant  of  any  other.  Just  as  in  this  chapter  we 
consider  the  receptive  organs  in  the  periphery  of  the  afferent  nervous 
system,  so  in  the  next  chapter  the  muscles  are  discussed — the  two  homol- 
ogous agents  of  the  individual  as  expressed  through  his  neural  fabric. 

These  are  the  afferent  nerve-endings  or,  less  correctly,  the  sense-organs. 
The  term  "sense-organ"  is  an  old  and  accepted  one.  From  the  modern 
view -point  as  to  the  relations  of  body  and  mind  it  is  somewhat  misleading, 
however,  since  it  implies  that  whenever  a  sense-organ  acts  it  represents 
a  conscious  sensation.  It  is  likely,  indeed,  that  this  is  so,  that  each  one 
of  the  millions  of  afferent  fibrils  in  the  nervous  system,  centripetally 
transmitting  some  impulse,  contributes  to  the  mass  of  consciousness. 
This  is  the  basis  of  the  notion  of  consciousness  to  be  found  stated  below 
(see  page  40.5).  If,  however,  we  always  think  of  the  impulses  passing 
inward  through  the  sense-organ  gates  as  afferent  rather  than  as  "sensory" 
we  shall  be  making  no  hypotheses  and  be  sure  we  are  thinking  rightly. 
This  is  the  more  important  because  it  is  becoming  more  and  more  appar- 
ent that  it  is  the  organism  which  is  conscious,  rather  than  the  mere 
nerve-cells,  and  that  at  any  rate  to  prove  that  the  efferent  impulses  are 
not  accompanied  by  "sensation"  is  quite  impossible,  ^^^lichever  theory 
of  the  mental  process  is  taken  as  the  basis,  in  the  majority  of  the  actions 
of  sense-organs  (including  of  course  the  cutaneous  and  tendo-muscular 


328 


THE  SENSES 


end-organs),  no  separable  conscious  impression  is  represented  by  the 
separate  afferent  organs.  Each  impulse,  however,  going  inward  more 
or  less,  probably  does  or  tends  to  do  something  in  the  organism.  Each 
is  useful  in  its  degree  and  probably  also  conscious  in  its  degree,  but  each 
is  not  necessarily  directive  of  the  attention  of  the  individual  so  as  to 
make  him  fully  conscious  of  any  sensation. 

Fig.  181 


Plan  of  tlie  afferent  jjaths  from  the  sense-organs,  showing  tlieir  morpliological  differences. 
(Peripheral  neurone-cell  in  back;  central  neurone-cell  in  wliite.)  .1,  "general  sensibility;"  B, 
taste;  C,  hearing;  D,  smell;  E,  vision;  ^lA'',  spinal  cord;  DD,  decussation  of  the  neuraxones  of 
the  central  neurones.      (Moral.) 


Another  matter  needs  an  introductory  word  for  clearness'  sake.  It  is 
the  province  of  anatomy  to  describe  the  structure  of  the  sense-organs.  It 
is  just  as  surely  the  duty  of  psychology  to  describe  their  function  which 
partly  is  consciousness.  But  physiology  in  this  case  ordinarily  does 
something  of  both,  for  the  mode  of  working  of  these  often  complicated 


KINESTHESIA  329 

organs  is  sometimes  quite  blind  without  a  general  notion  of  the  way 
they  are  built,  while  their  "function"  sometimes  is  indistinguishable 
from  sensation,  even  if  much  more  often  not.  Thus,  while  we  divide  the 
chapter  into  kinesthesia,  vision,  hearing,  and  so  forth  (functions),  our 
chief  concern  will  be  with  the  organs  serving  these  functions  and  especially 
with  the  ways  in  which  they  serve  them. 

The  senses  are  special  and  general.  The  former  have  end-organs, 
nerves,  and  cerebral  centers  somewhere  or  other,  probably.  The 
latter  arise,  in  ways  unknown  at  present,  more  or  less  throughout  the 
body. 

The  order  of  consideration  of  the  different  senses  is  intended  to  be 
that  of  their  probable  importance  in  the  conduct  of  the  organism's  life, 
although  the  positions  in  the  latter  part  of  the  list  are  confessedly 
arbitrary.  We  shall  discuss  kinesthesia,  vision,  hearing,  touch  and 
pressure,  taste,  smell,  the  temperature-senses,  pain,  pleasure,  and  the 
general  senses,  fatigue,  thirst,  hunger,  nausea,  and  vertigo. 

With  these  introductory  explanations  (necessarily  different  from  the 
preceding  parts  of  the  physiology  but  indispensable  as  a  basis  of 
departure),  we  shall  be  in  a  better  position  to  appreciate  the  importance 
of  especially  the  great  multitude  of  afferent  organs  other  than  the  eyes 
and  ears  and  taste-buds  and  smell-cells  on  which  the  organism  is  basally 
dependent  for  its  activities. 


KINESTHESIA. 

The  etymology  of  this  word  indicates  ''  the  feeling  of  movement." 
It  includes  then  the  afferent  impulses  of  the  organism  which  are  actuated 
by  its  movements.  These  movements  are  largely  produced  in  the 
muscles,  the  tendons,  and  the  joints.  We  shall  discuss  first  the  sense- 
organs  in  these  parts,  because  it  is  becoming  yearly  more  apparent  that 
they  have  more  to  do  wuth  directing  the  immediate  life  of  the  animal 
than  have  any  other  of  the  afferent  nerve-organs.  Their  mode  of  action 
in  connection  with  the  nerve-centers  we  saw  in  the  chapter  on  the  nervous 
system  and  we  shall  discuss  the  matter  further  in  relation  to  the  muscles 
in  the  next  chapter. 

Compared  with  the  great  sense-organs  of  vision  and  of  hearing,  these 
sensory  nerve-endings  in  the  muscles,  tendons,  and  joints  are  simple 
structures.  This  may  be  seen  from  the  accompanying  figures.  They 
are,  as  Huber  calls  them,  the  "  peripheral  teleodendria  of  dendrites  of 
peripheral  sensory  neurones."  The  forms  of  the  nerve-endings  already 
described  by  histologists  are  various  and  consists  of  two  general  varieties 
free  and  encapsulated.  The  free  endings  have  not  been  discovered  in 
muscles  or  tendons,  but  they  occur  in  mucosae  and  in  epithelium. 

Afferent  Exdings  in  Muscle. — These  are  of  several  forms  whose 
shapes  more  or  less  merge  into  each  other.  They  are  probably  all 
actuated  by  mechanical  pressure. 


330 


THE  SENSES 


Fig.  182  shows  well  the  cyHndric  end-bulb  of  Krause.  This  is  found 
in  cross-striated  muscle  and  in  tendon  as  well  as  in  the  skin  and  mucous 
membranes.  It  consists  of  a  thin  nucleated  capsule  investing  a  semi- 
fluid core  containing  the  nerve-fiber.  It  is  obvious  that  such  an  instru- 
ment among  the  fibers  of  muscle  or  tendon  will  be  stimulated  when  the 
muscle  hardens  in  contraction  or  when  the  fibrous  bundles  of  the  tendon 
are  drawn  together  as  the  tendon  is  put  on  stretch.  The  Vater-Pacinian 
corpuscle  is  built  on  the  same  plan  as  the  preceding,  but  it  is  on  a  larger 
scale  and  more  elaborate.      They  are  sometimes  3  mm.  long  and  1  or  2 


Fig.  182 


Fig.  183 


The  cylindrlc  end-bulbs  of  Krause.  The 
same  structure  is  seen  as  in  the  Vater-Paci- 
nian corpuscles,  but  this  sense-orgah  is  better 
adapted  to  its  position  between  muscle-fibers. 
These  are  perhaps  the  more  passive  end- 
organs  of  kinesthesia. 


A  Pacinian   coriiuscle   from  a  cat's  me.sentery. 
(Von  Frcy.) 


broad  and  have  as  many  as  60  fibrous  lamellae,  each  of  which  according 
to  Schwalbe  is  covered  on  both  surfaces  by  a  layer  of  endothelial  plates. 
These  end-organs  are  of  many  varieties  and  are  found  in  many  kinds  of 
places.  They  are  in  the  skin  especially  of  the  foot  and  the  hand  near  the 
joints  and  particularly  on  the  flexor  sides  f)f  the  latter,  in  the  periosteum 
(>{  the  bones,  in  the  tendons  of  intermuscular  septa,  in  the  muscles  them- 
.selves,  and  in  the  coverings  of  the  viscera  and  of  the  nerves  (Figs.  183, 184, 
and  208).  Of  a  different  nature  (and  function  who  can  doubt?)  are  the 
neuro-mu.scular  andneuro-tendinous  end-organs  described  \)y  Sherrington 
and  Golgi.    Instead  of  being  compact  and  rounded  organs,  these  apparently 


KINESTHESIA 


331 


are  the  means  by  which  the  nerve  ends  freely  among  the  muscular  and 
tendinous  fibers.  These  are  the  so-called  muscle-spindles  of  Kiihne  and 
Sherrington.     To  each  of  these  end-organs  go  two,  three,  or  four  large 


Fig.  184 


"S^"^  *o- 


Two  Pacinian- Vater-Herbst  corpuscles.  The  nerve-fibers  (neuraxones)  are  seen  to  di\ade  in- 
side the  connective-tissue  organ  in  various  ways,  each  division  ending  in  a  knoblet.  (Dogiel.) 
There  are  many  forms  of  this  general  afferent  nerve-instrument  variously  known  by  the  three 
names  given  above.      These  are  concerned,  perhaps  passively,  in  muscular  control. 

medullated  nerve-fibers,  which,  after  dividing,  end  in  fibrils  wound  about 
the  fibers  of  the  muscle  or  else  in  irregular  disks.  They  are  found  in  nearly 
all  cross-striated   muscle  save  the 

intrinsic  eye-muscles  and  those  of  Fig.  i85 

the  tongue  and  larynx.  They  are 
especially  abundant  in  the  delicate 
muscles  of  the  hand  and  the  foot. 
Kerschner  supposes  that  these  are 
stimulated  by  the  electrical  action- 
current  of  the  muscle  rather  than  by 
compression.  It  is  suggestive  that 
these  are  found  only  in  cross-stri- 
ated voluntary  muscle.  Perhaps  they 
represent,  therefore,  the  active  con- 
traction of  the  muscle  rather  than 
its  passive  movement  (Fig.  186). 

Afferent  Endings  in  Ten- 
dons.— The  neuro-tendinous  nerve 
end-organs  ("the  Golgi  organs"  of 
Sherrington)  are  constructed  on  a 

similar  general  plan.  These  are  found  only  in  tendons  and  they  too  are 
especially  numerous  in  connection  with  the  small  muscles  of  the  hand  and 
foot  (Fig.  187). 


A  sense-cell  in  the  upper  vocal  cord  of   a  dog, 
showing  the  nerve-net  about  it.      (Ploschko.) 


332 


THE  SENSES 


The  Atferext  Exdixgs  ix  the  Joixts,  etc. — Less  is  known 
about  these  than  about  the  end-organs  of  the  muscles  and  tendons. 
Kolhker  has  described  the  sensory  nerves  of  bone.  In  the  periosteum 
nerves  are  also  found,  but  they  are  smaller  and  less  numerous.  There 
are  in  the  joints  the  so-called  articular  end-bulbs  which  are  in  connec- 

FiG.  186 


A  muscle-spindle  from  a  cross-striated  muscle  of  a  dog:  a  and  b  are  coils  of  the  nerve  fiber 
making  up  the  "spindle,"  while  sy.n.,  is  a  sympathetic  vasomotor  fiber.  (This  may  be  the 
organ  through  wliich  cross-striated  muscle  is  actively  and  delicately  controlled.)  (Gluber 
and  De  Witt.) 

tion  with  the  Pacinian  corpuscles  already  described.  The  four  articular 
regions  (bone,  periosteum,  synovial  membrane,  and  skin  over  the  joints) 
probably  combine  to  send  to  the  brain  important  knowledge  of  the 
movements  of  the  limb  at  a  joint. 

Kinesthetic  Function. — Such  are  the  most  important  of  the  known 
afferent  organs  serving  the  kinesthetic  sense.     The  general  purpose  of  all 


Ftg.  187 


A  neurotendinouH  end-organ  from  the  tendo-Achillis  of  man:  sR  and  oH ,  two  nerve  fibers; 
jpl,  a  primitive  fibrillary  bundle  of  the  tendon;  rfnc,  the  ultimate  ribbon-shaped  branches  of  the 
nen'e-fibers.      (Ciacio  via  Barker.) 

these  afferent  impulses  is  to  furnish  the  person  information  as  to  the 
postures  and  relative  activity  of  his  limbs  and  other  bodily  muscular 
parts.  More  essential  than  these  ideas  of  posture  orrlinarily  are  the 
impressions  we  receive  from  these  end-organs  concerning  the  movements 
of  our  limbs  and  mu.scles,  active  or  passive,  of  which  the  active  are  the 


KINESTHESIA  333 

more  important.  ^Muscular  action ,  reflex  or  voluntary,  depends  for  its  use- 
fulness in  nearly  all  cases  upon  its  guiding  coordination  from  the  central 
nervous  system.  In  the  complex  voluntary  actions  of  life  especially  one 
sees  the  essential  importance  of  these  myo-tendo-articular  impulses  or 
sensations,  for  skill,  culture,  and  even  civilization  itself  in  part  depend 
on  the  fine  adjustment  of  voluntary  muscles  in  ever  new  and  more  delicate 
ways.  Imagine  a  "laborer"  accustomed  only  to  the  rough  use  of  the  pick 
and  shovel  in  a  trench,  attempting  to  engrave  a  delicate  monogram  on 
a  small  seal-ring.  The  inability  in  such  a  case  might  be  due  wholly  to 
the  lack  of  this  complex  sense  of  delicate  voluntary  movement.  These 
conditions  are  present  every\\^here  and  always  in  our  motor  activities. 
Take  for  another  example  the  act  of  walking.  This  is  almost  a  reflex 
action  in  the  person  more  than  three  years  old.  (See  the  description  of 
the  process,  page  392.)  As  one  walks,  continuous  streams  of  impulses  are 
passing  upward  into  the  gray  matter  of  several  segments  of  the  cord  and 
into  the  cerebellum  and  probably  into  the  posterior  and  anterior  central 
cortex  cerebri.  These  come  from  every  part  of  every  muscle  and  tendon 
of  the  legs  and  from  many  of  those  of  the  trunk  and  neck  engaged  in  the 
body's  equilibrium.  From  all  the  joints  concerned  (hip-joints,  knees, 
ankles,  feet,  spine,  etc.)  other  sets  of  impulses  pass  similarly,  and  from 
the  skin,  especially  over  the  joints  and  wherever  it  comes  in  contact 
with  our  garments.  Moreover,  we  are  kept  dimly  aware  of  the  nature 
of  the  path  we  walk,  whether  hard  or  soft  or  rough  or  smooth,  by  these 
same  sets  of  impulses.  These  too  help  reflexly  to  direct  the  spinal  and 
other  centers  in  their  complex  task  of  control  over  these  multifarious 
walking-parts.  One  may  similarly  trace  the  same  process  in  speaking, 
swallowing,  chewing,  and  numerous  other  movements,  as  well  as  in 
thousands  of  purely  voluntary  actions  known  to  the  many  trades,  occupa- 
tions, and  amusements.  It  is,  in  short,  only  on  the  information  furnished 
by  these  numberless  incoming  messages  that  the  centers  directing  move- 
ment can  do  their  work.  \ATien  w^e  make  voluntary  movements,  espe- 
cially with  the  arms  and  hands,  the  eyes  usually  follow  the  movements 
and  we  are  apt  to  think  that  it  is  by  vision  that  they  are  directed.  They, 
however,  can  be  made  even  better  in  many  cases  after  some  practice, 
without  any  use  of  the  eyes  whatever.  Unless  there  were  sent  into  the 
kinesthetic  centers  information  of  an  exact  nature  concerning  the  relative 
degree  of  contraction  of  each  muscle-fiber,  these  central  motor  cells 
could  not  properly  actuate  the  muscles.  A  partly  contracted  fiber,  for 
example,  would  need  a  different  degree  of  stimulus  from  one  contracted 
fully.  Xot  only  must  a  number  of  different  muscles  be  made  to  contract, 
but  each  one  often  in  a  particular  way,  hard  enough  but  not  too  hard 
and  each  at  exactly  the  right  time  and  for  exactly  the  right  period. 
In  short,  a  maze  of  relations  exists  which  would  make  of  a  movement 
not  thus  minutely  directed  by  afferent  messages  a  mere  jerk  or  con- 
vulsion. Never  would  we  have  the  wonderfully  adapted,  perfect,  and 
certain  action  we  are  familiar  with.  The  concertos  of  de  Pachmann 
differ  from  the  drumminof  of  our  fair  hut  misguided  neighbor  in  the  next 


334 


THE  SENSES 


house  chiefly  because  in  tie  Pachmann  this  sense  we  are  considering  is 
developed  to  its  human  limit,  while  in  her  apparently  it  is  not. 

Another  use  of  the  muscular  nerve-impulses  combined  with  those  from 
the  tendons,  joints,  etc.,  is  the  direction  of  the  power  of  contraction  need- 
ful to  overcome  a  required  resistance,  as,  for  example,  that  of  gravity  in 


Fig.  188 


Diagram  of  the  chief  kinesthetic  nerve-impulses.  From  the  joints,  muscles,  tendons,  and 
skin  nervous  influences  pass  inward  and  upward  to  the  "motor  centers"  of  the  cord  and  brain, 
making  general  connection  with  the  cerebellum  on  the  way.  Numerous  "central"  impulses 
connect  the.se  incoming  messages  with  other  parts  of  the  brain,  motor  and  sensory,  and  especially 
with  the  regions  wliich  control  the  efferent  influences  to  muscle  and  to  epithelium.  The 
impulses  passing  down  and  out  likewise  have  much  to  do  with  the  cerebellum.  This  whole 
apparatus  together — end-organs,  afferent  influences,  centers,  central  impulses,  efferent  influences, 
and  muscles — constitutes  the  neuro-muscular  mechanism. 


lifting  a  weight.  '"J'his  estimate  is  made  by  the  intell(>ctual  "centers"  of 
the  brain,  but  only  from  repeated  experiences  given  through  the  afferent 
muscular  and  other  senses.  The  effort  is  expended  under  the  guidance 
of  impulses  coming  from  the  contracting  mu.sc-le. 

That  kinesthesia   has  separate  centers  somewhere  in   the  brain,  or 
else  separate  paths  up  the  cord,  is  made  evirient  l)y  the  occasional  cases  in 


VISION  335 

which  this  sense  alone  is  lost,  those  of  the  skin,  for  example,  remaining 
unharmed.  On  the  other  hand  the  skin's  sensations  are  sometimes 
lost  without  disturbance  of  the  kinesthetic  sense.  The  location  of  these 
centers  is  still  in  doubt,  but  evidence  is  accumulating  that  it  is  in  the 
posterior  central  convolutions,  and  possibly  also  in  front  of  the  Rolandic 
fissure  on  the  cortex  cerebri. 

One  would  expect  these  centers,  moreover,  to  be  very  closely  allied 
with  the  centers  of  voluntary  movement.  These  impulses  probably  pass 
up  in  the  long  paths  of  the  dorsal  columns  and  in  the  direct  cerebellar 
tracts. 

(For  further  facts  as  to  muscular  control  see  Chapter  XII.) 
Partial  loss  of  the  kinesthetic  sense  produces  a  greater  or  less  degree  of 
ataxia  or  imperfect  muscular  adjustment  and  coordination  such  as  is 
seen,  e.g.,  in  ataxic  aphasia,  in  locomotor  ataxia,  and  in  paralytic  dementia 
("paresis").  The  spinal  afferent  fibers  are  disturbed  or  destroyed  in 
these  conditions.  A  heightening  of  this  sense  beyond  its  normal  state  is 
produced  by  small  doses  of  alcohol,  and  is  felt  more  normally  whenever, 
because  of  a  lack  of  muscular  exercise,  the  irritability  of  the  muscles  and 
their  tonic  balancing  back  and  forth  is  increased.  This  condition  is  all 
too  familiar  to  persons  of  sedentary  habit.  They  feel  "  fidgety,"  and 
yet  nothing  is  necessary  to  relieve  the  unpleasant  feeling  but  vigorous 
muscular  exercise  with  its  accompanying  aeration  of  the  tissues  and  the 
removal  of  accumulated  metabolic  substances  from  the  muscles  and  the 
nerve-centers.  It  is  one  of  the  functions  of  these  essential  afferent  end- 
organs  then  to  incite  the  individual  to  a  normal  amount  of  physical 
exercise.  Thus,  indirectly,  one  maintains  the  normal  metabolism  in  the 
muscles  (about  half  the  mass  of  the  body)  and,  by  increasing  the  flow  of 
lymph,  invigorates  and  stimulates  all  the  essential  organs  of  the  body. 


VISION. 

^larkedly  in  contrast  in  some  respects  with  the  kinesthetic  sense  is 
the  queenly  sense  of  vision,  of  experiencing  the  flooding  light  of  day. 
The  organs  of  the  muscle-sense  and  its  congeners  are  minute,  simple, 
and  hidden.  They  send  inward  a  host,  one  may  almost  say  figuratively 
a  mass,  of  impulses,  most  of  them  singly  quite  "unfelt,"  to  direct  the 
body's  motions.  The  eyes,  on  the  contrary,  are  large  and  complicated 
end-organs,  stars  of  "the  human  face  divine"  which  somehow  (we  can 
never  imagine  how)  set  going  into  the  brain  nerve-impulses  which  give 
rise  to  that  flooding  and  overwhelming  sensation  we  call  light.  Vision 
at  first  seems  easily  "  queen  of  the  senses,"  and,  by  its  very  nature,  to 
many  the  larger  part  of  consciousness. 

The  organ  of  vision,  the  eye,  is  too  elaborate  an  instrument  for  detailed 
description  here,  and  consequently  we  shall  run  over  the  structure  of 
only  those  portions  of  the  organ  which  are  immediately  essential  to  its 
various  functions  as  the  end-organs  of  certain  afferent  nerves  and  brain- 


336 


THE  SEXSES 


centers.  For  adequate  knowledge  as  to  the  detailed  structure  of  the  eye, 
one  of  the  most  complicated  parts  of  the  wondrous  animal  body,  the 
reader  is  referred  to  text-books  of  anatomy  and  histology.  Study  of 
such  an  organic  mechanism  always  much  more  than  repays  the  time  and 
labor  which  may  be  put  on  it,  and  in  this  case  is  entirely  indispensable 
for  any  proper  understanding  of  the  visual  function.  Here  we  are  con- 
cerned only  with  the  way  in  which  its  most  essential  parts  enable  us  to 


Fig.  189 


Diagram  of  the  retina:  a,  rod-  and  cone-layer;  b,  external  limiting  memVjrane;  c,  external 
granular  layer;  d,  external  reticular  layer;  e,  internal  gianular  layer;  /,  internal  reticular  layer; 
g,  ganglion-cell  layer;  h,  nerve-fiber  layer;  i,  internal  limiting  membrane.  'J"he  pigment-layer  is 
not  represented.      (Bate.s.) 

see  the  world's  infinite  variety  of  form  and  color,  to  somehow  perceive 
objects  by  waves  of  light  sent  into  the  fx'ripliery  of  the  nervous  system. 

The  eye,  then,  is  e.s.sentially  a  photographic  optical  instrument  for 
impressing  on  the  extended  peripheral  termination  of  the  second  cranial 
nerve  an  image  of  whatever  is  placed  before  it.  The  nerve  then  conveys 
the  nature  of  this  image  to  the  brain,  and  vision  results.  In  order  that 
this  image  on  the  retina  may  be  always  clear,  the  eye  has  lenses  and  means 


VISION 


337 


Fig.  190 


of  accoramotlating  its  function  not  only  to  the  light's  brightness,  but  to 
the  distance  or  size  of  the  object.  Vibrations  in  the  hypothetical  "ether" 
of  space  occurring  between  392,000,000,000,000  and  757,000,000,000,000 
times  per  second  give  the  eyes  their  proper  stimulus.  Vil>rations 
outside  this  narrow  range  we  do  not  perceive  as  light,  but  as  heat, 
electricity,  or  other  manifestations  of  vibratile  energy.  The  tendency 
now  is  to  think  of  this  ether  as  attenuated  matter  streaming  in  radia- 
tions from  the  sun. 

(The  common  refractive  defects  of  human  vision  and  their  remedies 
with  lenses  will  be  found  described  with  sufficient  detail  for  our  purpose 
in  the  Appendix,  page  o26,  etc.) 

The  Receptive  Apparatus  of  the  Eye  (as  distinct  from  the  transmitting 
mechanism)  consists  of  the  retina  and  the  optic  nerve  and  tracts  and  the 
centers  behind  them.  Of  all  the  complex 
structures  of  the  retina  (not  yet  much 
understood),  the  visual  cells  are  the  essen- 
tial portions.  These  are  the  rods  and  the 
cones.  Each  rod-cell  consists  of  a  rod 
and  a  rod-fiber  with  its  nucleus.  The 
rod,  averaging  45  microns  long,  is  made 
up  of  two  segments,  the  outer  of  which 
(doubly  refracting)  consists  of  numerous 
transverse  disks,  while  the  inner  segment 
is  striated  longitudinally.  The  rod-fibers 
extend  downward  to  the  outer  nuclear  layer 
(see  Fig.  190)  where  they  end  in  tiny 
bulbs.  The  rods  contain  in  their  outer 
parts  the  essential  pigment  called  visual 
purple  or  rhodopsin,  and  granules  in  their 
inner  ends.  The  cone-cells  consist  each 
of  a  cone  and  a  nucleated  cone-fiber. 
The  cone  averages  20  microns  long,  and 
its  fiber,  like  that  of  the  rod,  extends  in- 
ward to  the  outer  nuclear  layer  of  the 
retina  where  it  ends  in  a  branched  basal 
plate.  The  proportion  of  rods  to  cones 
varies  much  in  the  different  retinal  regions. 
In  the  macula  lutea,  the  sole  region  of 
sharply  focused  vision,  there  are  no  rods, 
but  in  other  parts  an  average  of  fourteen 
rods  to  one  cone  are  found,  but  fewer  cones  the  farther  away  from 
the  macula  a  region  lies.  It  is  noteworthy  that  the  cones  contain 
no  visual  purple.  The  rods  and  cones  are  the  only  ocular  elements 
capable  of  reacting  to  the  minute  vibrations  of '  the  luminiferous 
ether,  but  how  they  do  so  is  quite  unknown — evidently,  however,  by  a 
transformation  of  force,  the  light  waves  becoming  waves  of  nervous 
impulse.  Al:out  seven  cones,  a  hundred  rods,  and  seven  of  the  pig- 
22 


Different  .*hape?  of  retinal  rods:  A, 
that  of  the  perch;  B,  man;  C,  pig; 
D,  green  rod  of  the  frog;  E,  red  rod 
of  the  frog;  a.  external  segment;  b, 
internal  segment;  c,  cellular  body. 
(Greeff.) 


338 


THE  SENSES 


A  perimeter  chart  with  records  for  a  right  eye:  B,  blind  spot.  The  unshaded  portion  is  the 
field  of  clear  \-ision  for  white  light.  The  fields  for  yellow,  blue,  red,  and  green  light  respectively 
are  indicated  by  the  variously  broken  lines.  It  is  only  within  the  inner  circle  of  the  chart  that 
vision  is  direct  and  perfect.      (Krapart.) 

Ftg.  192 


Diagram  showing  relative  positions  of  the  eye's  refractive  media  and  the  reduced  refracting 
medium  (PPP).      Drawn  to  scale  and  five  times  the  natural  size.      (Hall.) 


T7.S/0A' 


339 


mented  cells  are  connected  with  each  of  the  half-million  or  more  fibers 
of  each  optic  nerve.  Many  details  of  the  structure  of  the  rods  and  the 
cones  are  known,  for  knowledge  of  which  the  reader  is  referred  to  the 
special  literature.  At  present,  however,  these  facts  of  structure  throw 
little  or  no  light  on  the  real  nature  of  vision.  We  can  see  the  rods  and 
cones  and  the  neurones  beneath  them,  but  as  to  their  actions  we  know 
nothing. 

The  fovea  centralis  is  the  center  of  the  macula  lutea,  and  is  the  spot 
on  which  the  visual  image  has  to  be  focused  whenever  the  object  is  to 
be  clearly  seen.  This  focusing  is  accomplished  by  several  sorts  of 
complex   movements. 

The  Various  Adjustments  of  the  Eyes. — As  has  been  just  suggested,  the 
fovea  centralis,  a  spot  only  a  few  millimeters  in  diameter  at  the  inner 
end  of  the  visual  axis  (not  of  the  optical  axis)  of  each  eye,  is  the  only  part 


Fig.  193 


The  extrinsic  eye-muscles,  and  the  eye-balls'  axes  of  rotation.      (Gariel.) 

of  the  whole  retina  at  which  vision  is  quite  distinct.  In  other  words,  the 
eyes  must  be  continually  so  directed  toward  any  point  of  an  object 
which  is  to  be  clearly  seen  that  the  rays  of  light  therefrom  shall  fall 
exactly  on  this  narrow  spot,  the  fovea.  There  must  therefore  be  some 
adequate  arrangement  for  quickly  and  reflexly  directing  the  eyes  in 
exactly  the  right  direction  if  vision  is  to  be  useful.  ^Moreover,  the  intensity 
of  the  light  entering  the  eyes  and  the  distance  of  the  ol^jects  looked  at 
vary  greatly  and  there  is  required  some  means  of  adjustment  to  these 
conditions  also.  The  former  sort  of  adjustments  are  made  by  move- 
ments of  the  head  and  of  the  eyes  within  the  head,  and  the  latter  kind  by 
means  of  the  accommodating  mechanism  proper  fthe  iris,  ciliary  muscle, 
etc.),  assisted  sometimes  by  the  muscles  of  the  eyelid. 

Head-:movemexts  for  visual  purposes  scarcely  need  detailed  descrip- 
tion.    The  possible  movements  of  the  head  upon  the  axis  at  the  top  of 


340 


THE  SENSES 


the  vertebral  column  are  very  numerous  and  in  all  directions.  It  is 
enough  to  know  that  for  the  most  part  the  muscles  producing  these 
movements  are  small  and  therefore  perfectly  adapted  for  any  desired 
movement.  They  are  controlled  by  what  is  practically  reflex  action. 
The  afferent  impulses  come  especially  from  the  retinae,  but  also  from  the 
voluntary  cortex  and  from  many  other  places  under  the  influences  of 
many  different  sorts  of  stimuli,  for  example  from  the  ears. 

Eye-movements  have  been  the  subject  of  a  large  amount  of  careful 
and  ingenious  study,  especially  by  the  psychologists.  For  example, 
Delabarre  attached  to  his  cornea  a  minute  concave  mirror  with  a  hole  in 
its  center  and  studied  the  directions  taken  by  a  ray  of  light  reflected  from 
it  on  to  a  photographic  plate.  The  movements,  however,  occur  so  often, 
so  quickly,  so  unconsciously,  and  are  often  of  such  small  extent,  that  real 
progress  in  the  subject  has  been  slow.  Knowledge  of  these  movements 
is  of  great  importance  in  many  theoretical  and  practical  problems,  for 
example  the  ideal  mode  of  composing  printed  matter  for  being  read. 


Fig.  194 


Inferior 
Obliqve  >~ 

(3)       ^- 


Superioi- 

Rectus 

(s) 


Internal 

->         -< 

Reetun  (  o  J 


}  Rectus     ]l- 

I  Inferior 

^'  (3) 

Diagram  of  the  actions  of  the  external  muscles  of  the  eye-ball, 
indicate  the  nerves  which  supply  the  muscles. 


Inferior 
pf  Oblique 


^  External 
^  Rectus 
(0) 


■^i\   Superior 
Oblique 

.    A) 


The  figures  in  parentheses 
(Waller.) 


Fig.  194  shows  well  the  gross  movements  as  produced  by  the  six 
extrinsic  eye-muscles.  The  nearly  spherical  globe  of  the  eye  is  set  in  a 
soft  bed  of  fat  and  of  vascular  tissue  and  rotates  with  great  readiness 
under  the  influence  of  the  muscles  (the  superior,  inferior,  internal,  and 
external  recti,  and  the  superior  and  inferior  obli(|ues)  attached  to  it. 
Thus,  the  internal  and  external  recti  rotate  the  eye  in  the  directions  their 
names  indicate;  the  superior  rectus  rotates  it  u])ward  and  inward,  and 
the  inferior  rectus  downward  and  inward;  the  superior  oblique  rotates  it 
downward  and  outward,  and  the  inferior  oblic|ue  upward  and  outward. 
In  the  majority  of  cases,  if  not  in  all,  the  muscles  work  in  com})ination, 
and  are  always  in  such  a  state  of  l)alancii)g  tonus  as  to  hold  the  eye 
functionally,  but  not  actually,  still.  The  muscles  of  the  two  eyes  always 
move  together,  but  their  contractions  become  less  efl'cctive  in  old  age. 
All  movements  normally  take  place  about  the  rotation-point,  11  mm.. 


VISION  341 

behind  the  front  of  the  cornea,  and  about  any  one  of  three  axes,  the  visual, 
transverse,  and  vertical. 

Besides  the  larger  movements  produced  by  the  extrinsic  muscles  and 
apparent  both  from  within  and,  to  others,  without,  there  are  numerous 
minute  unconscious  and  entirely  involuntary  movements  of  extreme 
cpiickness  and  jerky  in  nature,  whose  full  purpose  is  yet  by  no  means 
quite  clear.  They  are  discernible  only  by  delicate  means,  and  most 
readily  when  the  eye  is  made  to  fixate  rigidly  a  point  or  to  trace  carefully 
along  a  given  line.  It  is  likely  that  these  movements  are  intended  to 
avoid  the  tiring  of  the  sensitive  rod  or  rods  and  cones  of  the  retina  by 
distributing  the  stimulus  over  a  larger  number  than  else  would  be  inner- 
vated. Another  and  perhaps  a  more  important  function  of  these  minute 
movements,  of  which  the  seer  is  always  entirely  unconsciousness,  may 
be  to  help  the  synthesis  of  disparate  visual  impressions  into  a  "field  of 
vision,"  a  homogeneous  general  impression.  The  synthesis  of  actual 
vision  is  not  wholly  the  work  of  the  visual  centers  or  of  ''the  mind," 
but  in  part  at  least  of  the  afferent  end-organ  (retina)  as  well.  Experts 
in  these  matters  are  at  present  discussing  the  rather  primary  question 
as  to  whether  the  individual  sees  during  these  quick,  short,  intermittent 
eye-movements  or  during  the  very  short  periods  of  rest  between  them. 
Woodworth's  contention  for  the  former  seems  well-grounded  both  in 
theory  and  in  facts. 

Accommodation  is  the  reflex  adjustment  of  the  refracting  mechanism 
of  the  eyes  to  the  ever-changing  conditions  in  the  intensity  and  distance 
of  the  object.  The  mechanism  concerned  includes  the  ciliary  muscle, 
the  lens,  the  suspensory  ligament,  and  the  iris. 

The  chief  need  of  accommodation  lies  in  the  optical  fact  that  rays 
coming  from  an  object  near  the  eyes,  and  therefore  directed  in  more 
divergent  directions,  require  a  stronger  (convexer)  lens  to  converge  them 
upon  the  fixed  retina  than  do  more  nearly  parallel  rays  coming  from  a 
distance.  In  a  camera  or  in  a  compound  microscope  this  focusing  is 
brought  about  by  moving  the  lenses  away  from  their  screen  or  object, 
but  in  the  living  eye  it  is  more  convenient  to  change  the  refracting  power 
of  the  lens  itself.  This  change  is  easily  brought  about  because  of  the 
softness  of  the  lens-protoplasm,  especially  in  its  interior.  The  anterior 
capsule  of  the  lens  is  thick  and  some  of  its  lamellae  are  directly  continuous 
with  the  fibers  of  the  suspensory  ligament. 

The  theory  of  accommodation  originating  with  the  great  Helmholtz 
is  still  held  (in  a  condition  somewhat  modified  by  Hess,  Smith,  and 
Einthoven)  by  the  great  majority  of  physiologists.  The  accompanying 
illustration  (Fig.  195),  devised  by  Schoen  to  show  how  the  lens  changes 
shape  (on  a  theory  opposed  to  that  of  Helmholtz) ,  gives  a  good  notion  of 
what  appears  to  take  place  in  accommodation  to  near-vision.  The 
anterior  surface  of  the  lens  bulges  into  the  shape  shown  in  the  figure 
(although  in  a  degree  much  less  marked  of  course  than  that  shown). 
This  is  the  tendency  of  the  lens  itself,  because  of  its  structure,  whenever 
the  restraint  of  the  suspensory  ligament  and  the  ciliary  muscle  exerted 


342 


THE  SENSES 

Fig.  195 


Visual  accommodation:  m,  meridional  muscle;  c,  circular  muscle;  S.L.,  suspensory  ligament. 
The  position  of  the  lens  and  iris  as  shown  by  the  vertical  shading  is  the  position  when  accommo- 
dated to  a  near-point.      (Landolt.) 

Fig.  196 


Section  of  the  front  of  the  eye:  o,  cornea;  b,  .sclera;  c,  conjunctiva;  d,  iris;  e,  ciliary  body; 
f,  crystalline  lens;  (/,  ciliary  proces.ses;  i,  stratified  epithelial  covering  to  the  outside  of  the 
cornea;  j,  endothelial  lining  of  the  inside  of  the  cornea  forming  the  outer  wall  of  the  anterior 
chamber;  k,  canal  of  Schlemm.  It  will  be  seen  that  the  sclera  projects  forward  to  form  the 
cornea,  while  the  iris  comes  off  from  the  ciliary  body.  This  in  turn  is  a  forward  projection  of 
the  choroid.  The  dark  line  which  covers  the  inner  side  of  the  ciliary  processes  and  the  iris  is 
the  pigment  layer  of  the  retina.  /,  hludilvcs.scl  in  the  conjunctiva;  m,  suspensory  ligament 
which  holds  the  lens.      (Bates.) 


VISION  343 

about  its  edge  is  relaxed.  According  to  this  view,  then,  the  chief  activity 
of  the  cihary  muscle  is  to  relax  the  centrifugal  support  of  the  suspensory 
ligament,  thus  allowing  the  lens  to  bulge  somewhat  in  the  manner  shown. 

The  notion  of  Tscherning  and  of  Schoen  is  that  the  ciliary  muscle  in 
contracting  stretches  the  ligament  instead  of  relaxing  it,  and  that  it  is 
this  centripetal  pressure  on  the  edge  and  sides  of  the  lens  which  causes  its 
soft  substance  to  become  more  convex  in  accommodation  to  a  near-point. 
The  discovery  of  Hess,  that  when  the  ciliary  muscle  is  made  to  contract 
strongly  by  eserin  the  lens  wobbles  back  and  forth  within  the  suspensory 
ligament,  seems  to  dispose  of  this  supposition. 

With  the  increase  in  the  convexity  of  the  lens  in  accommodating  to 
near  objects  (amounting  at  its  maximum  to  an  increase  in  strength  of 
14  diopters  up  to  34  diopters)  occur  two  other  adjustments  of  the  eyes. 
One  of  these  is  the  convergence  of  the  eyes  necessary  to  place  a  near 
object  on  both  fovea.  This  is  produced  by  contraction  of  the  internal 
recti  muscles,  the  degree  of  convergence  depending  on  the  nearness  of 
the  object  seen.  The  internal  recti  are  relatively  strong  muscles  because 
used  so  much,  and  when  the  eyes  are  quite  at  rest  (as  in  sleep)  tend  to 
converge  the  eyes  mechanically  so  that  the  visual  axes  would  meet  if 
prolonged  40  cm.  from  the  eyes.  One  sees  this  atonal  condition  often, 
also,  when  persons  are  in  a  "brown  study,"  one  of  those  lapses  of  con- 
sciousness which  occur  at  times,  and  which  are  really  just  the  opposite 
in  nature  from  study. 

The  other  adjustment  which  is  properly  part  of  the  process  of  accom- 
modation is  contraction  of  the  iris  (pupil).  This  shuts  out  the  peripheral 
rays  from  the  eye,  prevents  spherical  aberration  and  so  makes  the  defini- 
tion of  the  object's  retinal  image  sharper.  The  iris  has  movements  other 
than  those  associated  with  accommodation.  It  serves  as  a  diaphragm 
for  adjusting  the  eye  to  differences  in  the  intensity  of  light.  Its  move- 
ments are  closely  watched  in  conditions  of  anesthesia  out  of  many  a 
serious  condition  involving  the  central  nervous  system.  Its  size  is 
affected  furthermore  by  many  drugs,  contracting  to  opium,  nicotine, 
and  muscarine,  and  dilating  to  atropine.  (See  the  experiments  in  the 
Appendix,  p.  521.) 

Visual  Theories. — \^Tien  one  has  summarized  thus  briefly  some  of  the 
most  essential  structures  of  the  eye  and  some  few  of  the  principles  on 
which  these  structures  work  he  has  had  suggested  to  him  many  interesting 
phenomena,  but  he  has  still  left,  Cjuite  unconsidered,  the  essential  part  of 
vision,  namely,  how  and  in  what  different  ways  the  eyes  see.  In  other 
words,  we  would  have  explained  to  us,  if  we  might,  exactly  what  takes 
place  in  the  minute  retinal  rods  and  cones  when  the  rays  of  light,  thus 
carefully  admitted  to  them,  stimulate  them  and  cause  them  to  send  to  the 
visual  centers  of  the  brain  the  several  different  sorts  of  vision  that  most 
of  us  experience.  For  example,  if  our  eyes,  etc.,  are  normal  we  see  light, 
the  forms  and  colors  of  objects,  and  the  spatiality  of  objects.  We  can 
see  in  the  dazzle  of  noonday  and  form,  at  least,  in  the  quasi-darkness  of 
night.     We  experience  after-images  and  our  eyes  are  prone  to  be  deceived 


344  THE  SENSES 

in  numberless  illusions.  We  suspect  that  chemical  processes  take  place 
in  the  retina  when  light  falls  on  it.  What  then  exactly  are  these  processes 
in  terms  of  modern  chemistry?  Why  are  there  no  rods  in  the  fovea? 
AMiy  do  diiierent  zones  of  the  retina  see  particular  colors  only?  Why 
do  we  not  experience  a  hole  in  our  monocular  landscape  where  the  blind- 
spot  is  ?  Is  color-blindness  a  defect  of  the  retina  or  of  the  brain  ?  Ques- 
tions of  which  these  are  only  important  examples  beset  us  everywhere 
while  observing  the  immensely  complex  facts  of  vision.  Their  explana- 
tion, however,  in  statements  to  which  all  must  agree,  are  quite  beyond 
us  as  yet. 

The  perceptiox  of  light  depends  in  some  w^ay  on  the  chemical 
changes  produced  in  some  substance  found  in  the  rods  or  the  cones  or  in 
both  by  the  vibrations  of  the  ''ether"  entering  the  eye.  This  is  probably 
some  chemical  change,  but  just  what  is  by  no  means  certain  as  yet.  It 
appears  to  be  in  the  nature  of  a  bleaching  of  a  pigment.  In  addition 
the  etheric  vibrations  cause  the  outer  parts  of  the  rods  to  increase  in 
diameter  and  the  inner  parts  to  thicken  and  shorten;  on  the  other  hand, 
the  lower  parts  of  the  cones  contract.  These  movements,  like  those  of 
the  pigment,  depend  much  on  the  nervous  system.  The  bleaching  of 
the  visual  purple  is  not  at  all  so  influenced.  It  is  obvious  how  inadequate 
such  statements  are.  Such  chemical  reactions  and  other  movements, 
whatever  they  are,  could  do  practically  nothing  toward  explaining  the 
wonderful  experience  we  call  light,  but  they  would  have  great  interest 
for  the  physiology  of  the  nervous  system. 

Theories  of  Color-vision. — These  have  been  numerous,  those  of 
Young,  Helmholtz,  Hering,  Wundt,  and  Mrs.  Franklin  being  perhaps 
the  most  conspicuous.  Out  of  these  theoretical  complexities  we  need 
discuss,  even  briefly,  no  more  than  the  last-mentioned. 

^Irs.  Franklin's  theory  of  color-vision  takes  account  of  various  facts 
recently  learned  which  give  it  much  weight  and  promise,  perhaps  more 
than  any  other.  It  is  likely  that  the  child  for  many  wrecks,  perhaps 
months,  after  birth  lacks  the  color-sense.  This  theory  supposes,  then, 
that  the  visual  substance  present  at  birth  in  the  retina  is  afl'ected  at  first 
only  by  light  ranging  in  tone  from  white  to  black  through  the  grays, 
but  that  the  substance  decomposes  through  this  kind  of  photic  influ- 
ence and  so  stimulates  the  optic  nerve-fibers.  In  the  first  or  second  years 
of  life  some  of  this  gray-perceiving  retinal  substance  develops  into  two 
other  retinal  pigments,  one  for  blue-p('rce])tion  and  one  for  yellow. 
A  little  later,  part  of  the  yellow-seeing  substance  in  turn  diflerentiates  into 
a  green-perceiving  sul)stance  and  a  red-perceiving  substance.  All  of 
these  pigments  except  the  gray-perceiving,  congenital  one,  develop  in  the 
cones.  This  theory,  then,  supposes  that  it  is  the  cones  of  the  adult  retina 
that  rey)rcs('nt  color,  while  the  rods  react  only  to  light-waves  of  the  black- 
white  sort.  Each  color-sensation  correspfjiids  to  one  combination  of 
ether  wave-lengths  striking  the  retina,  every  anabolic  and  katabolic 
color-process  being  dependent  for  its  stimulation  on  certain  vibration- 
numV>ers  in  the  ether.     There  is  no  end  to  the  number  of  combinations 


HEARING  345 

of  physical  rays  which  may  occur,  and  consequently  no  theoretical  limit 
can  be  set  to  the  color-tones  perceptible  by  the  human  eye.  (In  practice 
about  150  tones  of  color  can  be  distinguished,  and  700  degrees  of  bright- 
ness; the  total  number  of  elementary  chromatic  sensations  is  in  the 
neighborhood  of  30,000.)  Whenever  the  combination  of  wave-lengths 
in  a  beam  of  compound  light  is  such  that  each  sort  of  pigment  is  stimulated 
equally  at  the  same  time,  the  sensation  of  whiteness  is  produced. 

Color-blindness  is  a  technical  defect  of  much  practical  and  theo- 
retical importance  in  which  a  person  lacks  the  pow^r  to  perceive  certain 
colors.  About  one  in  twenty  of  all  males  are  more  or  less  color-blind, 
but  not  more  than  one  in  four  hundred  of  females.  It  is  often  heredi- 
tary. The  most  common  form  is  that  in  which  a  confusion  of  red  and 
green  occurs.  One  of  the  points  in  favor  of  Mrs.  Franklin's  theory  is 
that  it  explains  the  various  sorts  of  color-blindness  apparently  better 
than  any  other  hypothesis,  for  it  is  necessary  only  to  suppose  a  partial 
or  complete  non-evolution  of  the  color-pigments  of  the  cones. 

Space-perception. — It  is  probable  that  the  human  eye  does  not  at 
first  perceive  the  third  dimension  of  space,  that  is  depth  away  from  the 
eye.  To  the  infant  just  born  most  likely  the  objects  of  the  room  appear 
as  if  they  were  differently  colored  spaces  on  a  screen  hung  before  its 
eyes.  It  is  only  when  a  child  begins  to  use  his  muscles  that  the  idea  of 
space  in  three  dimensions  begins  to  grow  up  in  the  mind.  The  sensations 
which  come  from  the  muscles  of  the  arms  and  of  the  legs  in  action  are 
probably  assisted  in  this  matter  by  the  accommodative  movements  of  the 
eye-muscles.  This  in  a  word  is  the  so-called  empiric  theory  of  space- 
perception.  The  nativistic  theory,  on  the  contrary,  supposes  that  the 
perception  of  space  is  directly  given  visually  from  the  moment  the  eyes 
are  first  opened. 

HEARING. 

Only  less  informing  than  vision  as  to  occurrences  in  the  environment 
is  the  experience  called  sound.  Its  nature  we  cannot  discuss  here  any 
more  than  we  can  that  of  light,  for  that  is  the  province  of  philosophy. 
It  is  enough  to  say  that  what  comes  to  our  afferent  nervous  end-organs 
(ears)  out  of  the  environment  is  not  sound  but  physical  vibrations,  usually 
in  the  air.  We  and  other  animals  make  the  sound  and  the  light,  in 
some  way,  out  of  these. 

These  sonorous  vibrations  of  the  environment  are  given  out  by  all 
rapidly  vibrating  elastic  bodies:  huge  masses  of  gaseous  matter  in  the 
clouds  disturbed  by  lightning,  the  air  in  a  great  organ-pipe,  the  head  of 
a  drum,  the  string  of  a  %aolin,  or  the  cords  in  a  singer's  or  speaker's 
larynx.  These  and  thousands  of  other  natural  and  artificial  objects 
moving  rhythmically,  or  otherwise,  fast  or  slowly,  make  waves  in  the  ear*s 
environment  which  the  individual  perceives  as  sound,  whether  noise  or 
music.  These  waves  given  out  by  moving  objects,  like  hollow  spheres, 
radiate  outward  in  all  directions  (in  air  at  the  rate  of  332  meters  (1093 


346 


THE  SENSES 


feet)  per  second),  and  consist  in  alternate  rarefactions  and  compressions 
of  the  air.     The  vibrations  move  back  and  forth  in  the  Hne  of  advance. 


Fig.  197 


/',;;";''/'/'■'.•■ . 


Fio.  198 


A  suggestion  as  to  the  nature  of  sound-vibrations  as  distinct  from  those  j^roducing  light 
(which  are  vertical  to  the  ray's  direction).  Moreover,  the  sonorous  vibrations  are  those  of 
material  particles  of  air,  while  those  of  light  are  of  the  ether,  perhaps   not  of  a  material  nature. 

(while  in  case  of  light,  the  vibrations  are  at  right  angles  to  the  line  of 
advance).  For  the  range  of  the  human  ear  these  waves  vary  in  length, 
that  is  from  crest  to  crest,  from  about  1.5  cm.  to  more  than  12  m.; 

their  number  varies  from  about  16  to 
35,000  (even  50,000?)  per  second.  In  case 
of  noises,  all  sounds  which  have  not  the 
qualities  of  musical  tones,  the  conditions 
are  more  complex  and  various  and  in  fact 
little  understood.  It  is  supposed  that  the 
vibrations  producing  them  are  irregular 
in  many  ways,  while  those  making  tones 
are  essentially  rhythmic  however  complex 
the  rhythm.  It  is  presumed  by  many 
that  it  is  the  ampullae  of  the  semicircular 
that  represent  noise,  these  being  homolo- 
gous to  the  hearing-organs  of  many  of  the 
molluscs  and  other  simple  animals.  (See 
Figs.  221  and  222.)" 

As  in  case  of  vision,  we  may  divide  the 
ear  for  descriptive  physiological  purposes 
into  a  transmitting  ])art  and  a  receiving 
part.     The  conditions  are  relatively  sim- 
ple until  we  come  to  the  essential  nerve 
end -organ   of  Corti.      Even  this  we  can 
sketch    in    merest  outline    only,   for   this 
structure,  minute  as  it  is,  makes  the  ear  perhaps  the  most  complicated  of 
all  known  mechanisms.    At  any  rate  it  has  a  complexity,  even  that  which 
is  known,  far  beyond  the  power  of  man  at  present  to  understand. 


Diagram  to  suggest  the  compound- 
ing of  sound-waves  out  of  simpler 
forms.  In  this  case  the  bottom  curve 
(4)  represents  the  combination  of  the 
other  three  curves,  these  Vjeating  in 
the  ratio  of  1,  2,  and  3.  (McGregor 
Robinson.) 


HEARING 


347 


TpE   TRAXSMITTIXG  APPARATUS    AND  FUNXTIOXS  OF  THE    EAR   include 

the  pinna  and  the  external  auditory  meatus  (making  up  the  outer  ear), 


Fig.  199 


Diagram  of  the  grosser  mechanism  of  the  ear:  au,  auricle  or  pinna;  go,  external  auditory 
meatus;  tr,  membrana  tympani;  h,  malleus;  a,  incus,  attached  to  the  head  of  the  stapes  whose 
foot  is  in  the  foramen  ovale  of  the  labyrinth;  h' ,  p,  p' ,  perilymphatic  space  of  the  labyrinth;  c, 
membranous  labyrinth;  c',  one  of  the  three  semicircular  canals;  u,  utricle;  s,  saccule;  ph,  drum 
or  middle-ear  cavity;  eus.  Eustachian  tube  extending  to  the  posterior  nares;  el,  endolj-mphatic 
duct  extending  to  a  blind  bulbous  ending  between  layers  of  dura  mater  above;  ac,  eighth  cranial 
or  auditory  nerve  shows  its  two  parts,  cochlear  and  vestibular.      (Czermak.)       _^ 

Fig.  200 


Diagram  of  the  internal  ear:  RT,  scala  tympani;  RV,  scala  vestibuli;  CC,  canalis  cochlearis;  OC, 
Corti's  organ;  GC,  Corti's  ganglion;  S,  sacculus;  UT,  utriculus;  VA  and  VP,  two  of  the  three 
semicircular  canals;  ma,  auditory  maculae;  ca,  auditory  crests  of  the  ampullae;  GS,  Scarpa's 
ganglion.      (Duval.) 


348  THE  SENSES 

the  membrana  tympani,  the  interesting  structures  within  the  middle 
ear,  the  iMistachian  tube  leading  from  the  latter  to  the  pharynx,  and  the 
endolymph  of  the  inner  ear.  Here,  as  elsewhere,  the  reader  is  referred 
to  adequate  descriptions  of  these  mechanisms  to  be  found  in  anatomical 
works.     (Plate  IX.) 

The  organ  of  Corti  is  the  proper  afferent  end-organ  of  the  audi- 
tory nerve,  all  the  rest  of  the  ear  being  but  a  mechanical  means  of  securing 
the  proper  stimulation  of  this  minute  and  obscurely  intricate  structure. 
AVe  shall  note  here  only  a  few  of  the  very  numerous  details  of  this  organ — 
those  which  seem  most  important.  Erected  on  the  membrana  basilaris 
(which  extends  the  length  of  the  spiral  of  the  cochlea)  are  two  rows  of 
chitinous  pillars  called  the  rods  of  Corti.  These  are  connected  above, 
while  the  tunnel  of  Corti  runs  between  them  below.  The  inner  row  is 
made  up  of  about  7000  of  these  pillars;  the  outer  has  about  4600  of  them. 
From  the  summit  of  this  arch  extends  inw^ard  and  outward  a  thin  mem- 
brane (also  of  chitinous  material),  the  membrana  reticularis,  and  through 
minute  holes  in  this  net  extend  the  numerous  bristle-like  filaments  of 
long  cylindrical  epithelial  cells  beneath.  These  cells  recline  more  or 
less  on  the  outer  sides  of  the  pillars  of  Corti,  and  are  called  respectively 
the  inner  anrl  outer  auditory  cells  or  hair-cells.  Each  has  several  unique 
structures  within  it  whose  significance  is  quite  unknown.  There  are 
about  18,000  of  the.se  cells;  one  row  of  the  inner  cells  and  three  or  four 
rows  of  the  outer.  Between  the  hair-cells  are  scattered  certain  support- 
ing-cells, named  for  Deiters.  The  fibrils  of  the  auditory  nerve  pass 
from  the  ganglion  spirale  within  the  lamina  spiralis  to  the  bases  of  the 
hair-cells,  and  the  filaments  on  the  summits  of  these  cells  are  apparently, 
the  nerve  being  afferent,  the  beginnings  of  the  cochlear  branch  of  the 
auditory  nerve.  Above  the  filaments  extends  outward  from  the  lamina 
spiralis  at  the  base  of  Reissner's  membrane  (separating  the  scala  media 
from  the  scala  vestibuli  aVjove  it)  the  soft  membrana  tectoria,  striated 
and  cuticular,  and  apparently  free  in  the  endolymph  of  the  scala  media. 

The  membrana  basilaris,  on  w^hich  as  it  curves  about  in  the  spiral 
of  the  cochlea  Corti's  organ  is  placed,  is  made  up  of  transverse  fibers, 
about  24,000  innuml)er.  AVere  this  membrane  uncoiled  and  spread  out 
it  woidd  suggest  in  its  structure  and  shape  a  xylophone.  Contrary  to 
what  one  might  expect,  the  longest  fibers  are  at  the  apex  of  the  cochlear 
spiral  and  the  shortest  at  its  base.  The  extreme  lengths  of  these  fibers  are 
0.0.5  mm.  long  and  0.45  mm.  It  is  hard  not  to  suppose  on  the  principle 
of  analogy  that  the  respective  lengths  of  these  fibers  of  the  membrana 
basilaris  do  not  correspond  in  some  way  and  degree  to  the  differences  in 
pitch  of  sounds,  but  this  is  by  no  means  sure. 

IIow  l)r)Ks  TiiK  C)i{(;an  of  Corti  Act? — To  this  fjuestion  many  have 
replied,  but  all  differently.  A  notion  of  its  mode  of  working  perhaps 
more  common  than  others  is  that  which  follows,  little  altered  in  all  the 
V)usy  years  since  the  master  of  sonology,  Ilelmholtz,  suggested  it:  AVhen, 
started  by  a  vibrating  body,  an  air-wave  strikes  against  the  membrana 
tympani,  through  the  agenc-y  of  (lie  cjaljorate  bony  levers  of  the  middle 


PLATE   IX 


Plan  of  the  Endolymphatic  and  the  Perilymphatic  Spaces. 

(Testut. ) 

1,  utricle;  2,  saccule;  3,  semicircular  canal;  4,  canalis  cochlearis ;  5,  ductus endolymph- 
aticus;  6,  saccus  endolymphaticus ;  7,  canalis  reuniens  (Hensen's);  8,  scala  tympani;  9, 
scala  vestibuli;  10,  helicotrema;  11,  aqueductus  vestibuli;  12,  aqueductus  cochlearis; 
13,  periosteum;  14,  dura  mater;  15,  stapes  with  its  base  in  the  foramen  ovalis;  16, 
membrane  in  the  fenestra  rotundum. 


HEARING 


349 


ear,  the  stapes  is  slightly  but  powerfully  pressed  into  the  perilymph  of 
the  scala  vestibula  through  the  fenestra  ovalis.  The  pressure  is  almost 
instantly  communicated  to  the  very  thin  and  elastic  Reissner's  membrane 
and  passes  into  the  endolymph  of  the  scala  media  (containing  Corti's 
organ),  through  it,  and  into  the  perilymj)h  of  the  scala  tympani  below. 
As  it  passes  through  the  membrana  basilaris  (bearing  the  organ  of  Corti), 
it  causes  to  vibrate  that  particular  transverse  fiber  of  this  continuous 
membrane  which  corresponds  by  its  length  most  exactly  to  the  vibration- 
number  of  the  original  producer  of  the  sound.  This  fiber  of  the  mem- 
brana basilaris  (more  or  less  accompanied  by  several  fibers  on  either 
side),  rises  slightly  and  Avith  it  rise  the  pillars  of  Corti  and  the  hair-cells 
attached  to  them  above. 

As  to  what  happens  further  than  this  there  is  a  still  greater  disagree- 
ment of  opinion.     Perhaps  these  cells  are   pressed    against  the  mem- 


FiG.  201 


Organ  of  Corti :  s'.  ganglion;  SP,  nerve-fibers;  CC,  Corti's  canal;  Z,  Z',  laminse  basilares;  SZ.V, 
hearing  cells;  V,  supporting  cells;  mt,  membrana  tectoria;  cr,  cresta  spiralis.  (B.  Haller.)  The 
membrana  reticularis  (just  over  the  hair-cells)  is  not  shown.  This  diagram  represents  one  out  of 
several  theories  of  the  organ's  structure  and  action.  One  chief  doubt  is  as  to  whether  the  hairs 
of  the  hair-cells  (SZ)  are  continuous  with  the  fibers  of  the  membrana  tectoria,  7nl. 

brana  tectoria,  the  latter  then  either  damping  the  vibrations  of  their 
filaments  or  pressing  them  downward  against  the  nerve-fibrils  below. 
Perhaps  the  membrana  tectoria  is  the  vibrating  part  of  the  organ. 
Perhaps  it  is  the  filaments  only  of  the  hair-cells  which  vibrate,  or  even 
the  rods  only.  One  or  two  experts  have  claimed  that  the  ligamentum 
spirale  (by  which  the  membrana  basilaris  is  attached  to  the  outer  wall 
of  the  cochlea)  contains  muscle-cells,  and  that  therefore  it  probably 
serves  to  tighten  the  transverse  fibers  of  that  membrane.  Much  of 
importance  remains  to  be  learned  about  the  auditory  hair-cells  especially, 
not  only  as  to  their  filaments  but  as  to  their  very  complicated  internal 
structure.  About  the  function  of  the  pillars  of  Corti  and  the  tunnel 
between  them  information  is  also  sorely  needed  before  any  satisfactory 
theory  of  the  organ  of  Corti  can  be  suggested.  In  all  these  parts  (and  in 
many  others  we  have  not  even  named  here)  there  is  a  mechanism  whose 


350  T'^E  SENSES 

intricacy  in  some  measure  corresponds  with  the  mathematical  complexity 
of  the  air-waves  producing  the  sensations  of  tone  and  of  noise  which  we 
continually  experience. 

Certain  Qualities  of  Sounds. — All  sounds,  practically  speaking 
(that  from  a  tuning-fork  is  sometimes  excepted),  have  within  them  ele- 
ments both  of  tone  and  of  noise.  "No  player  of  the  violin  avoids  all 
noise  of  scraping  from  the  bow;  no  stroke  of  a  workman's  hammer  or 
slamming  of  a  door  that  does  not  start  and  catch  up  into  itself  some  trace 
of  musical  sound."  But  noises  for  the  most  part  remain  unstudied 
and  their  relation  to  the  ears  is  almost  unknown.  They  constitute, 
however,  especially  in  cities,  no  inconsiderable  portion  of  the  sounds  with 
which  the  ear  has  to  do. 

Tones  or  musical  sounds  have  three  basal  characteristics:  intensity, 
pitch,  and  quality  (timbre).  The  intensity  of  a  tone,  depends  wholly 
upon  the  amplitude  of  the  air-vibrations  which  move  the  membrana 
tvmpani.  This  amplitude  must  not  be  confused  with  the  frequency  of 
the  vibrations,  for  it  has  nothing  to  do  with  it. 

The  'pitch  of  musical  sounds  (noises  lack  especially  this  quality) 
depends  wholly,  so  far  as  we  know,  on  the  number  of  vibrations  per 
second  produced  in  the  organ  of  Corti  by  the  sonorous  body.  The 
discrimination  of  differences  in  pitch  varies  very  widely  in  different 
persons.  Some  cannot  distinguish  between  two  contiguous  whole  tones, 
while  in  some  parts  of  the  scale  many  musicians  can  distinguish  differ- 
ences dependent  on  one-third  of  a  single  vibration-number,  a  variation 
of  about  0.00066  per  cent. 

This  faculty  of  discriminating  pitch-differences  is  in  most  persons  cap- 
aV)le  of  a  great  degree  of  development,  but  by  what  parts  of  the  ear  this 
improvement  is  accomplished  is  not  known.  The  fact  of  its  possibility 
would  seem  to  imply  that  the  various  muscles  of  the  ear  (perhaps  fibers 
in  the  ligamentum  spirale  among  the  rest)  have  much  to  do  with  auditory 
adjustments,  because  the  muscles  are,  to  say  the  least,  much  more  fully 
under  voluntary  control  than  other  sorts  of  tissue  in  the  organism. 
Many  of  the  lower  animals  {e.  g.,  cats  and  numerous  sorts  of  insects) 
can  hear  sounds  far  too  high  for  the  human  ear,  while  others  are  very 
sensitive  to  jars  we  should  not  notice.  Recent  highly  valuable  WTitings 
of  Helen  Kellar  (learned  and  capable,  although  deaf  and  blind)  reveal 
how  much  the  jars  and  unsonorous  vibrations  of  things  of  our  environ- 
ment may  teach  us  when  they  have  a  chance.  They  were  partly  repre- 
sented in  the  auditory  nerve,  although  largely  it  appears  by  the  kines- 
thetic sense-organs  in  the  joints  and  muscles. 

The  qualitij  of  tones,  technically  called  timbre,  depends  on  many 
various  conditions,  part  of  which  are  unknown.  '^i""he  difl'erence  in  the 
quality  of  tones  is  illustrated  in  the  unicjueness  of  each  human  voice 
and  by  the  variations  in  the  same  note  when  sounded,  for  instance,  on  a 
violin,  a  cornet,  a  piano,  an  organ,  and  a  harp.  Another  sort  of  qualita- 
tive difference  is  expressed  by  the  word  voluinr,  illustrated  by  the  diflcr- 
ence  between  the  sound  of  a  vocal  scjIo  and  that  of  a  chorus,  or  between 


TOUCH,  PRESSURE,  AXD  LOCATION  351 

that  of  a  small  ami  a  large  orchestra,  when  the  intensity  does  not  difier. 
How  all  these  differences  are  represented  bv  the  mechanisms  of  the  ear 
is  Cjuite  unknown. 

The  direction  from  which  sounds  come,  biologically  often  of  great 
importance,  is  given  the  individual  by  his  comparison  of  the  respective 
intensities  of  the  sensation  in  the  two  ears,  ^^^len  these  are  equal  it 
is  considered  that  the  sound  is  originated  either  directly  in  front  or 
directly  behind  the  middle  of  the  head. 

The  Perceptiox  of  Obstructions. — Another  experience  given  us 
by  the  ears  is  that  of  perceiving  without  aid  from  the  eyes  an  obstruction, 
such  as  a  wall  or  even  a  book  held  broadside  close  by.  There  is  in  this 
a  feeling  of  being  shut  in.  This  sensation  probably  comes  from  inappre- 
ciable sound  reflected  from  the  object  into  the  ear  or  ears.  It  is  expe- 
rienceable,  however,  when  no  sounds  are  audible  as  such,  and  when  all 
air-currents  are  excluded.  It  probably  corresponds  to  some  special 
adjustment  of  the  apparatus  in  the  middle  ear  O^iHiam  James). 


TOUCH,  PRESSURE,  AND  LOCATION. 

These  senses  are  probal)ly  only  aspects  of  but  one  sensory  experience. 
When  the  stimulus  is  of  weak  intensity  and  of  short  duration  we  perceive 
^'touch,"  and  when  it  is  strong  enough  to  bend  the  skin  downward  we 
fell  it  as  "pressure,"  but  in  every  case  there  is  inherent  in  the  sensation, 
W'C  know  not  how,  awareness  also  of  the  location  on  or  in  our  bodies 
of  the  stimulus  (its  "local  sign").  In  general,  then,  it  will  be  understood 
in  what  follows  that  the  two  last-mentioned  aspects  of  the  sensation  are 
always  involved,  although  we  may  use  only  the  term  touch.  Included  also 
in  a  list  of  the  various  afferent  end-organs  of  this  sense  of  location  should 
be  included  those  of  the  joints  and  muscles  in  some  cases  perhaps,  but 
these  have  already  l)een  described  under  kinesthesia. 

Organs  and  Functions. — At  various  times  and  by  different  observers 
there  have  been  described  at  least  seven  sorts  of  afferent  nerve-endings 
which  probably  are  concerned  with  tactile  sensibility.  It  is  possible 
that  some  of  these  are  concerned  with  the  temperature-senses,  or  with 
pain,  etc.,  but  for  this  there  is  at  present  no  direct  evidence.  The  seven 
or  eight  probable  tactile  end-organs  are  as  follows:  Meissner's  corpuscles, 
the  spheric  end-bulbs  of  Krause,  the  Vater-Pacinian  corpuscles  (includ- 
ing the  Golgi  and  ^lazzoni  and  other  variants),  the  elastic-tissue  spindles 
of  Ruffini,  the  nerve-rings  of  Bonnet,  and  the  tactile  menisci.  Two  of 
these,  the  cylindrical  end-bulbs  and  the  Vater-Pacinian  corpuscles,  are 
found  also  in  muscle  and  in  tendon,  and  have  been  described  already. 
We  find  in  these  various  organs  none  of  the  mechanical  or  chemical 
intricacy  so  discouraging  in  trying  to  understand  Corti's  organ  and  the 
retina,  but  we  do  find  much  uncertainty  about  their  specific  functions. 
The  presence  of  these  afferent  nerve-endings  in  so  large  a  variety  sug- 
gests once  more  in  a  striking  way  the  complexity  of  the  means  by  which 


352 


THE  SENSES 


the  functions  of  the  nervous  system  are  controlled,  and  in  part  also  the 
constitution  of  consciousness.  The  analysis  of  both  of  these  aspects, 
the  neural  and  the  mental,  await  the  fruitful  attention  of  modern  research, 
^leissner's  corpuscles  consist  essentially  of  a  spiral  or  twisted  plexLis 
of  the  fibrils  of  from  one  to  five  medullated  nerve-fibers  enclosed  in  a 


Fig.  202 


—  /ust 


Ner\-e.s  and  tlieir  ending.s  in  the  human  skin:  hst,  epidermis;  rm,  germinativc  layer  (Malpighii); 
c,  superficial  plexus  of  nerve-fibrils;  n,  cutaneous  nervelet;  h,  as,  is,  a  hair  and  [its  sheath s;;_^dr, 
.sebaceous  glands.      (Retzius.) 


thin  huiK'iiatcd  connective-tissue  capsule.  These  are  found  in  the 
tactile  papillae  of  the  true  skin.  Rows  of  them  make  up  the  concentric 
lines  to  Vjc  seen  on  the  distal  phalanges  of  the  fingers.*^^  Every  fourth 
papillais  tactileand  contains  one  or  sometimes  two  corpuscles  of  Meissner. 
There  appear  to  be  in  this  region  about  twenty-one  in  every  square  milH- 


TOUCH,  PRESSURE,  AND  LOCATION 


353 


meter  of  skin,  while  in  the  middle  of  the  foot-sole  there  are  about  two 
in  this  unit  of  area.  The  spherical  end-bulbs  of  Krause  are  of  a  similar 
general  structure  to  the  preceding.  (See  Fig.  215.)  They  are,  however, 
shaped  somewhat  diii'erently,  being  spherical,  oval,  or  pear-shaped .  They 
are  located  more  deeply  than  the  preceding  sort  of  end-organ.  The  cylin- 
drical end-bulbs  of  Krause  were  described  on  page  330,  which  see.  The 
Pacinian  corpuscles,  of  which  there  are  many  varieties,  have  also  been 

Fig.  203 


A  Meissner  corpuscle:  a  and  a  ,  are  nerve-fibers  which  break  up  above  into  a  complicated 
system  of  loops  and  knoblets.  The  whole  is  surrounded  by  connective-tissue  lamellae,  inside  the 
papilla.  Rows  of  these  make  up  the  lines  on  the  finger-ends,  etc.  (Probably  the  end-organ 
of  gross  touch.) 

described  under  the  head  of  muscle-sense  organs.  (See  page  330.) 
These  are  apparently  the  most  elaborate  of  the  tactile  organs,  and  are 
often  lars'e  enough  to  be  seen  with  the  naked  eve.  The  Vater-Pacinian 
corpuscle,  the  corpuscle  of  Herbst,  and  the  Golgi-^Iazzoni  corpuscle 
are  various  forms  of  these  last,  and  differ  chiefly  in  the  structure  of  the 
core  and  in  the  relative  thickness  of  the  transmitting  mechanism  around 
it.  The  elastic-tissue  spindles  fRuffini)  are  found  in  the  corium  and 
23   . 


354 


THE  SENSES 


often  closely  associated  with  the  Pacinian  corpuscles.  They  consist  of 
a  connective-tissue  frame-work  on  which  a  plexus  of  teleodendria  is 
arranged  about  the  elastic  fibers.  Another  organ  bearing  Ruffini's  name 
is  the  plume-organ  so-called.  This  von  Frey  suggests  may  be  the  end- 
organ  of  heat.  Xerve-rings  of  the  hair-follicles  (Bonnet)  (Fig.  206) 
have  been  recently  described.  These  for  the  first  time  suggest  a  use- 
ful function  of  the  lanugo  hairs  found  on  nearly  all  parts  of  the  body, 
the  hand-palms  and  the  foot-soles  being  marked  exceptions.  These 
end-organs  consist  essentially  of  a  ring  of  nerve-fibrils  forming  a  narrow 


Fig.  204 


Fig.   205 


The  afferent  nerves  and  Pacinian 
corrjuscle.s  of  the  third  finger.  (Henle 
and  Kolliker.) 


Tactile  corpuscles  of  three  degrees  of  complex- 
ity (diagrammatic):  A,  corpuscle  of  Grandry  with 
one  tactile  disk,  dt,  and  two  tactile  cells,  ci;  B, 
corpu.scle  with  two  disks  and  three  cells;  C,  Meiss- 
ner's  corpuscle;  1,  2,  3,  its  component  parts 
(Orandry's  corpuscles);  n,  nuclei  of  the  tactile 
cells;  a,  nerve-fiber;  si,  interannular  segment. 
(Duval  via  Morat.) 


cylindrical  plexus  in  the  wall  of  the  hair-follicle  just  below  the  ducts  of 
the  sebaceous  glands.  When  the  hair  is  bent,  as  by  a  touch  on  the  skin, 
its  shaft  acts  as  a  lever  and  compresses  on  one  side  this  ring  of  nerve- 
fibrils.  The  tactile  menisci  or  disks  are  the  most  superficial  of  the 
cutaneous  sense-organs  of  touch.  They  each  consist  of  an  epithelial 
cell  placed  upon  a  delicate  meniscus,  each  disk  being  connected  below 
with  a  nerve-fiber  (Fig.  207).  The.se  are  placed  in  the  lowest  portions 
of  the  epidermis.  In  ad(h'tion  to  the  foregoing,  it  is  likely  enough  that  a 
certain  free  nerve-ending  in  the  cornea  (Fig.  2H))  and  pos.sibly  also  an 
encapsulated  end-organ  figured  by  Longworth  represent  touch. 


TOUCH,  PRESSURE,   AXD  LOCATIOX 


355 


Some  of  these  are  found  in  the  body's  interior,  but  in  small  numbers. 
Many  regions  of  the  viscera  are  quite  devoid  of  touch-sensation. 

All  these  kinds  of  end-organs  are  probably  connected  by  special 
nerve-fibrils  to  the  cord.  The  impulses  pass  up  by  columns  and  to 
centers  already  descril)ed,  and  may  stop  in  the  posterior  frontal 
convolutions,  but  it  is  unlikely  that  these  kinds  of  sensation  have 
any  sharply  defined  areas  of  cerebral  representation. 


Fig.  206 


Fig.  207 


Tactile  disks  from  the  epithelium  of  the  pig's 
snout:  mk,  the  tactile  disks;  z,  epithelial  wall; 
n,  nerve.      (Tretjakoff.) 


Touch-spots. — Goldscheider  in 
1884  showed  that  the  skin  is  dotted 
with  minute  areas  each  of  which 
possesses  a  sort  of  sen.sation  pecu- 
liar to  itself — touch,  heat,  cold,  or 
pain  (see  below).  There  is  still 
more  or  less  disagreement  as  to  the 
arrangement  of  these  "spots,"  but  as 
later  study  shows  that  these  areas 
may  be  reduced  to  mere  spots,  each 
is  undoubtedly  some  one  of  the  end- 
organs  just  described.  On  running 
a  needle  ground  especially  fine  into 
one  of  these  spots  no  suggestion  of 
pain  (nor  of  warmth  nor  of  cold)  is 
felt,  but  a  strong,  sharply  localized  sensation  of  pressure  vmaccom- 
panied  by  any  other  sensation  than  that  of  its  relative  location  on  or 
in  the  body.  Almost  always  there  are  one  or  more  touch-spots  close 
to  a  hair,  usually  on  the  side  from  which  the  hair  slopes,  and  they  also 
are  apt  to  be  arranged  in  certain  regions  in  short  lines  radiating  from 
the  hair-follicles,  ^^^lere  no  hairs  exist  the  arrangement  of  the  spots 
is  the  same. 

Certain  Tactual  Qualities. — It  is  plain  that  the  large  variety  of  the  touch- 
pressure-location   end-organs   noted    above   suggest   a   like   number   of 


The  nen'e-ring  (of  Bonnet)  about  a  large 
hair  of  a  dog:  o  and  b,  begin  to  ascend  the 
longitudinal  fibrils,  while  at  c  the  circular 
fibrils  may  be  seen.  (Probably  the  most  sen- 
sitive of  the  touch  end-organsj.      (Bonnet.) 


356 


THE  SENSES 


qualities  to  these  sensations.  These  quahties,  however,  are  unknown. 
Sensations  being  known  if  anything  is,  this  is  tantamount  to  saying  either 
that  some  of  these  described  afferent  end-organs  transmit  inward  to  the 
cord,  etc.,  impulses  which  give  rise  to  no  analyzable  portions  of  con- 
sciousness, or  that  some  of  these  organs,  either  directly  or  through  nerve- 
fibrils  connected  with  them,  represent  other  sensations  subserved  by 
the  skin:  of  heat,  cold,  pain,  tickling,  electricity,  pleasure,  or  what-not. 


Fig.  208 


Fig.  209 


"Golgi-Mazzoni  corpuscles"  found  by  Ruffini  in 
the  subcutaneous  connective-tissue  of  the  ball  of 
the  finger. 


Nerve-terminations  in  a  tooth  of  the  fish 
Gobius:  d,  dentine;  n,  nerve-fibers.  (Ret- 
zius.) 


At  present,  in  short,  the  specific  duties  of  some  of  these  end-organs 
described  by  good  observers  as  tactual  in  function  cannot  be  told  any 
more  than  can  their  relations  to  each  other,  to  the  touch-pressure  spots, 
and  to  the  brain. 

Landois  showed  that  the  finger  recognizes  as  separate  the  vibrations  of 
a  string  occurring  1.552  times  per  second,  while  induced  electrical  currents 
of  130  per  second  are  felt  as  disparate.  The  latent  period  and  the  sub- 
sidence-period of  touch-organs  are  then  both  very  brief. 


TASTE  357 

The  threshold-stimulus  for  the  different  parts  of  the  body-surface 
varies  widely.  In  general  the  sensitivity  of  a  tactile  region  is  roughly 
proportional  to  the  amount  of  its  use  in  touching  or  being  pressed  upon. 
Von  Frey,  using  Hensen's  method  of  stimulating  with  glass-wool  fibers 
ranging  in  surface  from  0.002  to  0.06  sq.  mm.,  found  the  following 
thresholds  for  various  regions. 

Grams  per  square 
millimeter. 

Tongue  and  nose ' .      .      .      .        2.0 

Lips •       2.5 

Finger-tip  and  forehead 3.0 

Back  of  finger 5.0 

Palm,  arm,  thigh 7.0 

Forearm 8.0 

Back  of  hand 12.0 

Calf,  shoulder 16.0 

Back  of  upper  arm  ) 

Abdomen  \ 26.0 

Outside  of  thigh      j 

Shin  and  sole 28 . 0 

Back  of  forearm 33 . 0 

Loins 48.0 

Wlien  it  is  remembered  that  sometimes  these  stimulating  fibers  were 
not  more  than  j-^q-q  sq.  mm.  in  area,  the  great  sensitivity  of  the  tongue 
and  nose,  for  example,  is  readily  seen.  In  some  cases  even  0.001  gram 
actual  pressure  is  readily  felt.  On  the  forehead,  tongue,  etc.  (Euten- 
berg),  an  increase  of  pressure  of  3  or  4  per  cent,  was  found  to  be  percep- 
tible. 

Two  points  at  the  skin-temperature  are  felt  as  two  (rather  than  as  one) 
when  only  1.1  mm.  apart  on  the  tongue-tip  of  a  man,  but  on  the  middle 
of  the  back  and  on  the  thigh  when  67  mm.  apart  they  are  felt  as  one. 

How  the  sense  of  location  is  served  by  these  organs  is  a  complete 
raiystery.  Every  spot  we  can  touch  on  the  skin  has  a  "local  sign"  (Lotze) 
by  which  the  individual  knows  just  where  on  his  body  that  particular 
spot  is  located.  However  produced,  and  whether  native  (congenital)  or 
acquired  by  infinite  touches  in  combination  with  vision,  muscle-sense, 
etc.,  it  is  a  strong  argument  for  the  theory  of  "the  specific  energy  of 
nerves"  in  its  newer  form  that  the  central  nervous  system  represents 
somehow  in  its  cells  and  fibers  the  whole  body. 


TASTE. 

The  sense  of  taste  furnishes  us  most  of  the  pleasure  derived  from 
mating,  which  in  turn  assures  us  the  full  complement  of  the  food  required 
by  the  organism.  Its  end-organs  help  reflexly  to  cause  the  secretion  of  the 
digestive  juices.  Lastly,  it  serves  sometimes  as  a  means  of  discriminating 
between  the  beneficial  and  the  harmful  among  eatable  substances,  for 
most  proper  foods  are  pleasant  to  the  average  palate. 


358 


THE  SENSES 


EPSGLOTTHS. 


CIRCUM- 
VALLATE 
PAPILUE, 


Upper  surface  of  the  tongue. 
Fig.  211 


A  taste-bud  from  the  circumvallate  papilla;  of  the  tongue:  a,  surface  stratified  epithelium; 
b,  lower  layers  of  the  same;  c,  sensory  cells  surmounted  by  delicate  hair-like  processes;  d,  sup- 
porting cells.      (Bates.) 


TASTE 


359 


The  Gustatory  Apparatus  consists  chiefly  of  certain  afferent  nerve 
end-organs  called  taste-buds,  of  certain  afferent  nerves,  and  of  the 
central  regions  to  which  they  transmit  their  impulses. 

The  taste-buds  (Schwalbe)  are  minute  flask-shaped  organs 
composed  of  four  sorts  of  elongated  fusiform  cells,  of  which  three  are 
perhaps  sustentacular  in  function  and  only  one  gustatory.  The  buds 
average  about  0.075  mm.  deep  by  perhaps  0.040  mm.  in  diameter 
(see  Fig.  211).  The  gustatory  cells  proper,  neuro-epithelial,  are 
elongated  and  fusiform  with  the  nucleus  in  the  thickest  part  of  the  cell, 
and  have  stiff  slender  filaments  projecting  above  them  into  the  open 
taste-pore.  They  are  encircled  by  nerve-fibrils.  This  pore  is  often 
0.01  mm.  deep  and  is  filled  with  the  liquid  of  the  mucous  membrane 
around.  From  one  to  ten  of  the  taste-cells  are  found  in  each  bud.^ 
The  buds  are  found  on  the  back,  edges,  and  root  of  the  tongue,  on  the 
soft  palate,  the  uvula,  the  pillars  of  the  fauces,  the  under  surface  of  the 
epiglottis  (Nicholson)  and  posteriorly  in  small  numbers,  in  the  larynx, 
and  in  the  olfactorv  region  of  the  nose.     Thousands  of  them  are  found  in 


Fig.  212 


The  nerve-filaments  about  the  taste-cells.      In  A  the  taste-cell  is  indicated  also;   in  B  not. 

(Duval.) 


two  of  the  three  sorts  of  papillse  which  beset  the  tongue's  dorsum,  namely, 
in  many  of  the  fungiform  papillae  scattered  over  the  surface  of  the  tongue, 
and  especially  in  the  sides  of  the  circumvallate  papillae  of  the  back  of 
that  organ.  They  are  not  present  apparently  in  the  filiform  papillae, 
but  are  present  in  the  level  mucous  membrane. 

The  nerves  of  the  sense  of  taste  are  still  not  certain.  There 
is,  however,  excellent  evidence  that  the  ninth  cranial  fglosso-pharvngeal) 
nerve  is  one  of  them,  supplying  the  rear  third  of  the  tongue.  The  pars 
intermedia  of  Wrisberg,  running  in  the  trunk  of  the  seventh  (facial),  is 
another  taste-nerve,  supplying  the  soft  palate  and  the  rest  of  the  tongue. 
The  doubt  now  lies  chiefly  as  to  whether  the  superior  laryngeal  branch 
of  the  tenth  (vagus)  nerve  carries  taste-impulses  or  not,  the  strong  prob- 
ability at  present  being  (Zwaardemaker)  that  it  supplies  taste  to  the 
region  of  the  central  circumvallate  papilla  (foramen  cecum),  to  the 
epiglottis,  and  to  the  inside  of  the  larynx.  The  trigeminal  (fifth  cranial) 
nerve  supplies  without  doubt  the  taste-buds  recently  found  in  the  olfac- 
tory region  of  the  nasal   mucosa   called  the  Schneiderian   membrane. 


360 


THE  SEXSES 


The  cerebral  center  of  the  gustatory  nerve-fibers,  it  is  Kkely,  will  be 
shown  to  be  low  down  on  the  mesial  surface  of  the  cortex  of  the  temporal 
lobe,  just  below  one  of  the  probable  centers  of  smell.  Von  Bechterew 
thinks  he  has  located  the  center  for  bitter  and  salt  in  the  anterior  Sylvian 
g}TUS  and  for  sour  and  sweet  in  the  anterior  ectosylvian  gyrus  (in  apes), 
in  the  region  of  the  operculum. 

Some  Characteristics  of  Taste. — A  substance  in  order  to  have  a  taste 
must  be  at  least  slightly  soluble  in  the  alkaline  fluid  of  the  mouth.  Thus, 
while  iron  gives  a  taste,  sulphur  does  not.  But  not  all  substances  solu- 
ble in  the  mouth's  secretions  have  tastes,  and  what  it  is  that  determines 
whether  or  not  a  substance  is  to  have  a  taste  is  cjuite  unknown.  There 
is  evidence  that  the  taste-cells  can  be  mechanically  and  electrically 
stimulated  to  give  gustatory  sensations.  This  is  an  indication  that 
the  taste  of  objects,  like  the  "light"  of  the  ether  and  the  "sound  "  of 
vibrating  objects,  is  subjective,  that  is,  resident  in  or  the  production  of 
the  perceiving  animal.  Still  sapid  substances  must  have  qualities  of  some 
sort  which  determine  their  tastes.  In  this  direction  Haycraft  finds 
reasons  to  suppose  that  the  compound  chemical  radicle  COOH  occasions 
the  acrid  taste  and  CH^OH  the  sweet  taste. 

No  classification  of  the  taste  acceptable  to  all  has  yet  been  made. 
In  the  nature  of  the  sensations  none  is  possible,  perhaps.  Some  classifica- 
tion may  one  day  be  made  on  the  basis  of  the  sensory  cells.  There  is, 
however,  fairly  good  agreement  that  four  classes  of  tastes  are  properly 
described,  namely  sweet,  bitter,  salt,  and  sour.  Seemingly  a  fifth  taste, 
metallic,  shoukl  be  added  and  perhaps  a  sixth,  alkahne,  although  more 
properly  perhaps  this  is  a  variety  of  salt  tastes.  It  is  probable  that  all 
the  tastes  are  represented  in  every  portion  of  the  gustatory  areas  above 
defined,  but  some  parts  give  one  taste  more  readily  or  more  strongly 
than  another.  Kiesow  found  the  following  threshold-values,  the  num- 
bers being  percentages  of  the  substances  in  distilled  water;  about  half  a 
cubic  centimeter  of  the  solution  was  used  in  each  case. 


Substance. 

Tip  of  the 
tongue. 

Edge  of  the 
tongue. 

0.24      too. 25 
0.76      toO.72 
0.007    toO.006 
0.0002 

Base  of  the 
tongue. 

Sodium  chloride 

Cane  sugar 

Hydrochloric  acid 

Quinine  sulphate 

0.25 
0.49 
0.01 
0.003 

0.28 
0.79 
0.016 
0 . 00005 

Perhaps  one  Vjud  or  even  one  taste-cell  has  to  do  with  only  one  sort  of 
taste.  Experimentation  is  difficult  and  more  or  less  uncertain  because 
when  the  papillae  are  with  difficulty  made  dry  they  are  abnormal,  but 
when  they  are  moist  the  liquid  carries  the  sapid  substances  used  as 
stimuli  to  more  than  one  enrl-organ. 

The  reaction-time  of  the  taste-buds  differs  with  different  substances: 
salt  is  tasted  most  promptly  and  V)itter  least  so.  There  are  after-images 
of  taste  as  there  are  of  vision  and  of  the  other  senses.     Various  contrast- 


SMELL 


361 


•effects  also  are  observed  here  as  in  the  other  senses.  Some  drugs  ahoHsh 
the  senses  of  taste  in  various  ways;  thus,  for  example,  cocaine  abolishes 
the  bitter  taste  first. 

SMELL. 


Fig.  213 


This  sense,  as  already  suggested,  is  far  less  important  in  the  conduct 
of  life  in  man  than  it  is  in  many  of  the  lower  animals.  Dogs,  for 
instance,  apparently  obtain  more  information  through  their  sense  of 
smell  than  even  by  vision.  In  man  it  serves,  much  as  does  taste,  to 
furnish  both  pleasure  and  protection  and  to  incite  to  fulness  of  function. 
In  this,  respiration  is  chiefly  served,  for  in  the  flowery  fields  of  summer  or 
the  spruce  forests  it  impels  the  organism  to  inhale  deeply  the  pure  air, 
while  in  places  where  the  air  would  harm  instead  of  benefit,  it  causes  us 
to  reduce  as  far  as  possible  its  intake 
and  to  escape  from  it  at  once,  More- 
over, when  the  air  is  sweet  it  incites 
respiration  through  the  nose,  its  proper 
organ,  rather  than  by  the  mouth.  As  a 
further  protection  it  warns  us  away  from 
putrid  food  unfit  to  be  eaten  and  from 
water  too  full  of  vegetable  matter  to  be 
proper  drink.  Its  sexual  relation,  very 
important  in  most  of  the  brutes,  is  nearly 
obsolete  in  civilized  man  except  in  the 
feminine  use  of  perfumes.  To  a  less 
extent  than  taste,  smell  serves  as  the 
sense  by  which  go  inward  the  impulses 
which  reflexly  start  the  secretion  of  the 
digestive  juices.  Thus,  the  odor  of  roast- 
ino^  meat  makes  a  hung-rv  man's  mouth 
"water"  and,  as  we  have  already  seen,  his 
stomach  as  well.  Helen  Kellar  empha- 
sizes how  useful  the  sense  of  smell  is  to 
her,  each  acquaintance,  for  example, 
having  a  unique  odor  appreciable  at 
some  distance. 

The  Olfactory  Apparatus  is  simple  so  far 
as  mechanism  is  concerned,  for  it  consists 
wholly  of  peculiar  cells  embedded  in 
mucous  membrane,  of  neurones,  and  of 
centers  in  the  brain. 

The  olfactory  cells  are  the  cell-bodies  of  non-medullated  neur- 
axes  whose  teleodendrites  are  in  the  olfactory  bulbs.  They  are  fusiform 
cells  each  with  a  round  nucleus  and  a  large  nucleolus  in  the  thickest  part 
of  the  spindle.  Toward  the  free  mucous  surface  the  cells  terminate  in 
blunt  cones  upon  each  of  which  stand  seven  or  eight  bristle-like  filaments, 


Olfactory  cells  from  the  Schneiderian 
membrane:  1,  from  that  of  a  dog;  2, 
frona  man;  h,  the  olfactory  cells;  a, 
supporting  cells.  The  hair-like  fila- 
ments, e,  on  the  upper  ends  of  the 
cells  extend  outward  on  the  moist 
surface  of  the  mucosa.      (Schultze.) 


362 


THE  SENSES 


the  so-called  olfactory  hairs,  extending  out  into  the  moisture  of  the 
nasal  cavities.  Sustaining  these  cells  in  place  are  long  columnar  epithe- 
lial cells  branched  toward  the  basement-membrane.  Among  the  branches 
of  these  are  other  cells,  broad  below  and  with  processes  above,  resting 
on  the  membrane,  which  are  of  unknown  use.  Round  about  in  places 
are  the  serous  glands  of  Bowman  or  olfactory  glands,  whose  cells  contain 
the  brownish  or  yellow  pigment  of  the  olfactory  region. 

The  regio  olfactoria  in  man  on  each  side  of  the  body  consists 
of  an  area  of  ("Schneiderian")  mucous  membrane,  folded  in  the  middle, 
and  about  2  cm.  long  by  1  cm.  wide.     One  sq.  cm.  of  the  area  is  on  the 

Fig,  214 


amb.  r/iio  .^ 


Tentative  scheme  of  the  principal  neurone-systems  of  tlie  olfactory  conduction-path. 

(Barker.) 


inside  surface  of  the  upper  part  of  the  middle  of  the  superior  turbinated 
bone  and  the  other  sfj.  cm.  is  directly  opposite  on  the  nasal  septum 
(von  Brunn).  Sometimes  minute  islands  of  the  olfactory  mucosa  are 
to  be  found  adjacent  to  this  tract.  In  these  areas  alone  are  the  olfactory 
cells  to  be  found.  The  region  is  in  color  a  brownish  yellow.  It  is 
placed  high  enough  on  the  superior  turbinated  bone  and  nasal  septum 
to  be  out  of  the  direct  current  of  inspired  air  and  especially  of  expired 
air,  yet  it  is  sufficiently  near  the  incoming  air-stream  to  be  continually 
bathed  in  a  slow  current,  and  this  is  the  condition  best  adapted  to  easiest 
smelling.  In  sniffing,  the  in-rush  of  air  is  more  sudden  and  probably 
reaches  directly  the  olfactory  mucosa. 


SMELL  363 

The  nerves  of  smell  are  the  first  cranial  pair.  There  are  three 
orders  of  neurones  between  the  olfactory  cells  and  the  centers  in  the 
temporal  lobes.  The  center  appears  to  be  placed  mesially  in  the  uncinate 
convolution  in  the  anterior  part  of  the  gyrus  fornicatus,  and  perhaps  on 
the  posterior  part  of  the  lower  surface  of  the  frontal  lobe  (see  page  73). 
The  sniffing-nerves  are  those  of  inspiration. 

Some  Conditions  of  Smell. — Nothing  is  known  as  to  the  precise  relation 
of  the  olfactory  cells  to  the  odoriferous  particles  which  stimulate  them. 
It  is  natural  to  suppose,  however,  that  the  reaction  of  the  olfactory  proto- 
plasm in  these  cells  is  chemical  in  its  nature,  the  odoriferous  particles  in 
some  way  altering  the  metabolism. 

There  is  no  hint  at  hand  as  to  the  physical  nature  of  these  particles 
themselves.  AMiatever  they  are  physically,  they  are  well-nigh  inexhaus- 
tible in  certain  cases.  One  thinks  inevitably  of  radio-activity  as  the  type 
of  the  process  possibly  concerned  in  this  sort  of  stimulation.  There  has 
been  much  discussion  also  as  to  the  form  in  which  the  odor-bringing 
substance  must  be  in  order  to  stimulate  the  smell-cells.  Zwaardemaker, 
for  example,  and  Weber  suppose  that  only  gases  and  vapors  stimulate, 
while  Aronsohn  claims  that  weak  solutions  give  up  their  odors  to  the 
cells.  Perhaps  some  particular  ions  convey  this  impression  to  the 
protoplasm,  or  at  least  must  be  present  for  its  conveyance.  Haycraft 
by  experiments  on  himself  determined  that  even  odorous  air  to  be  smelled 
must  be  in  motion.  0.00001  gram  of  mercaptan  disseminated  in  230 
cubic  meters  of  air  in  a  closed  space  give  a  weak  but  distinct  odor,  or  in 
the  proportion  of  0.00000000004  gram  to  the  liter  of  air.  This  suggests 
the  sensitivity  of  the  olfactory  cells  to  certain  substances,  for  only  a 
small  fraction  of  this  last  quantity  of  course  would  reach  the  olfactory 
region  at  any  one  time.  Passy  determined  the  threshold-values  of  eight 
common  odorous  substances  as  follows,  the  numbers  being  in  milligrams 
per  liter  of  air : 

Essence  of  orange 0.00005  to  0.001 

Essence  of  wintergreen       ....  0.00000.5  to  0.0004 

Rosemary 0.00005  to  O.OOOS 

Ether 0.000-3  to  0.004 

Peppermint-leaves 0.0000005  to  0.00001 

Camphor 0.005 

Natural  mask 0.01  to  0.1 

Artificial  musk  (trinitro-isobutyltohiin)  0.001  to  0.0005 

Attempts  to  classify  the  odorous  substances  have  been  made  by  many 
observers  (E.  Erdmann  and  Linnes,  for  example),  but  with  almost 
obvious  failure  always. 

Some  odors  completely  antagonize  others,  there  being  here  a  degree 
of  inhibition  found  nowhere  else  among  the  sensations  unless  in  vision. 
Thus  Zwaardemaker  claims  that  the  odor  of  musk. will  inhibit  the  odor 
of  bitter  almonds,  and  iodoform  the  odor  of  the  volatile  oils.  Some 
confusion  between  smell  and  taste  arises  because  of  the  probable  pres- 
ence of  taste-buds  in  the  mucous  region  heretofore  supposed  to  be  purely 


364 


THE  SENSES 


olfactory  in  function.     From  this  we  learn  why  so  many  persons  con- 
fuse, for  example,  the  strong  odor  and  the  weak  taste  of  boiled  onions. 

For  both  taste  and  smell  individual  differences  are  common  and 
marked.  Flavors  and  savors  delightful  to  one  person  to  the  next  may 
be  unpleasant.  One  becomes  quickly  accustomed  to  odors  at  first 
disagreeable,  so  that  they  lose  all  unpleasantness.  Smell-experiences 
seem  to  have  a  sort  of  arbitrariness  about  them  (somewhat  such  as  one 
meets  with  in  the  study  of  hysteria)  not  encountered  in  the  other  senses 
in  nearly  so  marked  a  degree. 


THE  TEMPERATURE-SENSES. 


Fig.  215 


The  human  skin  has  a  sense  of  warmth  and  a  sense  of  coldness. 
Although  probably  separate  more  or  less  in  end-organs,  nerves,  and 

centers,  these  may  be  well  discussed  to- 
gether, since  in  many  respects  they  are 
similar.  At  the  very  outset  in  trying  to 
give  the  general  usefulness  of  these  senses 
we  are  met  with  the  difficulty  that  al- 
though we  know  what  the  respective  heat 
and  cold  end -organs  represent,  we  do 
not  as  yet  certainly  know  their  general 
relation  to  the  organism.  When  we  feel 
cold  or  too  warm  it  is  doubtless  by  these 
end-organs  that  the  sensation  is  started 
inward  from  the  skin.  Their  probable 
relation  to  thermotaxis  has  already  been 
discussed  under  the  subject  of  body-heat 
(see  page  23 <S). 

The  Apparatus  of  the  Temperature-Senses, 
including  the  neural  connection,  is  proba- 
bly at  least  not  less  complex  than  is  that 
of  touch,  but  we  know  much  less  about 
it.  No  one  so  far  has  published  a  draw- 
ing and  labelled  it  as  a  representation  of 
the  end-organ  either  of  cold  or  of  heat. 
The  nearest  to  it  even  is  von  Frey's  sug- 
gestion that  certain  end-organs  described 
by  Ruffini  fsee  page  3o0)  antl  (more  likely)  the  suggestion  by  Sher- 
rington that  the  "genital  corpuscles"  of  Krause  (see  page  3GS)  might 
be  the  desired  afferent  end-organs  of  the  cold-sense.  Von  Frey  thinks 
it  possible,  too,  that  another  neural  structure  found  by  Ruffini  (plume- 
organ  ?j,  of  large  size  and  cylindrical  in  form,  deep  in  the  skin  of  the  eyelid, 
arm,  and  hand,  may  be  the  end-organ  of  the  lieat-nerves.  The  reason 
for  this  long  ignorance  lies  in  the  impossibility  of  isolating  and  stimulating 
by  any  known  means  in  man  (the  only  animal  who  can  tell  of  such  sensa- 


Krause's  end-bulbs:  A,  a  twisted 
form  showing  the  bluntly  ending 
nerve  fiber  and  the  lamellated  con- 
nective-tissue covering;  B,  a  cor- 
puscle containing  at  least  six  of  these 
end-bulbs.  (Szymonowicz.)  Perhaps 
the  end-organ  of  cold. 


THE  TEMPERATURE-SENSES 


365 


tions)  a  single  isolated  afferent  end-organ  of  any  sort,  because  of  its 
smallness  and  transparency. 


Fig.  216 


i     i" 


The  nerve-endings  of  RufEni  ("plume-organs")  from  the  subcutaneous  tissue  of  the  finger. 
They  have  strong  connective-tissue  sheaths  and  the  varicosities  end  in  knoblets.  (Ruffini.) 
Perhaps  the  end-organs  for  heat. 

Fig.  217 


Two  maps  showing  the  topography  of  the  temperature-sensations.  Each-  square  represents  a 
square  inch  of  the  back  of  the  left  hands  of  two  men.  Axis  of  the  hand  was  from  left  to  right. 
The  heat-spots  are  vertically  shaded,  the  cold-spots  horizontally,  while  the  dotted  areas  repre- 
sent tactile  sensibility.     The  tactile  spot  a  is  0.01  sq.  in.,  the  heat-spot  h  is  0.02  sq.  in.     (Hall.) 

The  nerves  of  the  thermic  organs  have  not  been  isolated  from  the 
afferent  trunks  going  into  the  cord  by  the  posterior  routes.  There  is 
good  evidence,  however,  that  each  of  these  sen.ses  of  heat  and  cold  has 


366  THE  SEXSES 

nerve-fibers  of  its  own.  These  impulses  probably  go  upward  in  the  cord 
either  by  the  numerous  short  neurones  in  the  posterior  part  of  the  gray 
matter  (more  or  less  as  pain  is  supposed  to  go)  or  by  the  posterior  median 
and  posterior  lateral  columns.  The  cerebral  centers  connecting  with 
these  organs  are  not  definitely  known  as  yet,  but  the  cutaneous  sensa- 
tions in  general  seem  to  be  represented  far  back  in  the  Rolandic  region. 
The  whole  bodily  surface  is  more  or  less  sensitive  both  to  heat  and  cold, 
as  is  to  a  degree  also  the  beginning  of  the  alimentary  and  respiratory 
canals. 

Fig.  218 


The  temperature-spots  as  Goldscheider  found  them  in  the  palm  of  a  hand: 
A ,  heat-spots;  B,  cold-spots. 

Fig.  217  exhibits  two  regions,  each  an  inch  square,  of  the  same 
locality  of  two  persons'  hands  (Hall).  It  shows  very  well  the  mosaic 
arrangement  of  the  three  cutaneous  senses  so  far  considered,  heat,  cold, 
and  touch.  Goldscheider  suggests  that  the  regions  in  which  none  of 
these  sense-spots  are  to  be  found  corresponds  to  the  blind-spot  of  the 
retina — regions  over  the  trunks  of  small  nerves,  which  are  lacking 
there  in  branches  and  end-oreans. 


PAIN. 

In  both  theory  and  practice  pain  is  of  considerable  importance. 
Several  theories,  biological  and  psychological,  might  be  discussed,  each 
involving  elements,  however,  beyond  our  present  range,  and  each  (save 
that  here  described)  ignoring  the  physiological  evidence  of  recent  years. 
With  one  of  the  theories,  that  of  the  evolutionists,  e.  </.,  Herbert  Spencer, 
we  may  say  that  pain  is  the  mental  accompaniment  of  hindered  biological 
function,  just  as  in  the  long  run  pleasure  is  the  accompaniment  of  fur- 
thered })iological  function.  The  object  of  pain,  then,  is  to  warn  the 
animal  of  threatened  organic  injury  or  of  injury  already  received.  The 
methcxl  })y  whirii  this  is  as  a  sensation  is  l^rought  about  is  that  of  other 
sensations:  end-organs,  nerves,  and  centers.  The  numerous  conflicting 
theories  as  to  pain  rest  on,  first,  the  ignoring  of  the  physiological  evidence, 
as  too  often  is  the  habit  of  purely  l)ook-instructcd  theorists.  Second, 
they  rest  on  the  confusion  of  the  sliarj),  biting,  actual  pain  with  the 
numberless  grades  of  unpleasantness  and  die  disagreeable.     One  is  an 


PAIN 


367 


indescribable  true  sensation,  the  other  a  complex  feeling  allied  to  the 
other  general  "sensations"  (see  below).  The  confusion  is  increased  by 
the  fact  that  oftentimes  both  the  sensation  of  pain  and  the  unpleasant 
feelings  may  he  experienced  at  the  same  time,  somewhat  as  a  man  may 
feel  fatigued  and  suffer  from  a  toothache  simultaneously.  But  if  we 
leave  these  numerous  compound  experiences  out  of  our  account  we  find 
pain  as  the  mental  aspect  of  the  functioning  of  certain  sense-organs, 
while  unpleasantness  is  a  psychological  subject  with  which  we  have 
just  here  no  concern.  Their  only  apparent  common  factor  is  that  the 
animal  experiencing  them  wishes  both  gone  and  changed  to  their  oppo- 
sites,  pleasure  and  pleasantness  respectively.  We  assume,  it  may  be 
too    dogmatically,    that    a    little 

positive   evidence  as   to  pain-ap-  Fig.  219 

paratus  is  worth  volumes  of  nega- 
tive theories  in  opposition  to  it. 
(See  also  Chapter  XII,  under 
Feeling,  page  409). 

The  Sensory  Apparatus  of  Pain 
was  tentatively  described  about 
the  same  time  as  was  that  of 
touch  and  of  the  temperature- 
senses,  Goldscheider's  name  and 
that  of  von  Frey  being  especially 
associated  with  its  discovery.  The 
peripheral  nerve-endings  or  the 
end -organs,  whatever  their  form, 
are  situated  apparently  in  "spots," 
as  are  those  of  the  other  senses 
named.  These  spots  are  scat- 
tered more  evenly  than  in  the 
other  cases  over  the  body's  sur- 
face, and  perhaps  to  a  slight  ex- 
tent within  the  viscera  of  the  body, 
especially  in  the  testis,  ovary,  kid- 
ney, and  rectum,  ^^^len  stimu- 
lated mechanically  or  electrically 
by  points  delicate  enough,  these 

spots  give  rise  to  a  smart,  tingling  pain  whose  one  only  quality  is 
that  of  pure  painfulness,  there  being  nothing  connected  with  it  like 
any  other  sensation  whatever.  (On  the  other  hand  the  touch-spots, 
heat-spots,  and  cold-spots  lack  this  pain-character  when  stimulated.) 
From  the  pain-spots  pressure-stimuli  as  small  as  that  of  150  grams 
per  square  millimeter  elicit  this  wholly  characteristic  pain-sensation. 
Several  circinnstances  besides  that  of  their  even  distribution  serve  to 
distinguish  them  from  the  other  cutaneous  spots.  Of  these  circum- 
stances, their  very  long  latent-period  is  perhaps  the  most  conclusive, 
for  it  is  most  easily  measurable  in  exact  terms.     Onlv  less  so  than  this, 


Afferent  nerve-endings  in  the  human  cornea, 
according  to  Klein,  oblique  section:  a,  nerve- 
fiber  (axis-cylinder);  b,  fibrils;  c,  terminal  net- 
work among  the  epithelial  cells,  d.  Perhaps 
these  are  the  endings  that  represent  pain. 


368 


THE  SENSES 


however,  is  their  liminal  intensity  for  electrical  stimuli,  which  is  lower 
than  that  of  touch. 

The  afferent  nerves  of  these  spots  are  unknown.  There  is  much  evi- 
dence, physiological  and  pathological,  that  the  impulses  pass  up  the  gray 
matter  of  the  cord  for  a  longer  or  shorter  distance,  perhaps  only  passing 
obliquely  through  it  or  across  it.  As  for  the  center  of  pain,  Budge 
found  evidence  in  animals  of  pain  from  stimulation  of  the  corpora  quadri- 
gemina,  but  this  evidence  is  inconclusive.  Many  things  go  to  show 
that  a  center  is  stimulatable  with  a  normal  result  only  by  the  stimulus 
coming  from  its  own  end-organ,  and  the  pain-stimulus  we  do  not  know 
how  to  imitate.     Cases  of  analgesia  (abolition  of  the  pain-sense)  are  in 

Fig.  220 


A  genital  sense-organ  from  the  glans  penis  of  a  man:  a,  sheath  about  the  nervelet;  h,  con- 
nective-tissue sheath  of  the  corpuscle;  c,  nerve-fibers  which  ramify  inside  the  end-organ.  If 
the  body  may  be  said  to  have  afferent  organs  of  a  pleasure-sense,  this  is  probably  one  of  them. 
(Dogiel.) 

themselves  alone  strong  evidence  that  a  neural  mechanism  of  pain  is 
part  of  the  nervous  system.  It  is  hard  to  think  how  an  abnormality 
could  ari.se  which  would  throw  out  of  action  only  one  set  of  experiences 
unless  the  nerve-arrangements  for  that  set  of  sen.se-impressions  were 
distinct  in  some  way.  Ca.ses  of  various  sorts  and  degrees  of  analgesia 
are  common  and  similar  to  the  sensory  paralysis  of  other  sets  of  nerves 
much  Vjetter  known  in  their  courses  and  endings. 

Besides  the  pain-spots  of  the  .skin,  some  of  the  mucosfe  and  viscera, 
notably  the  heart,  the  .serous  coverings,  and  mu.scle  obviously  have  pain- 
organs  as  a  part  of  their  complete  mechanism. 


VERTIGO 


369 


Pleasure. — The  theoretic  status  of  the  sensations  of  pleasure  is  more 
vague  and  doubtful  than  is  that  of  pain.  It  seems  probable,  however, 
that  pleasure  end-organs  exist  (Fig.  221),  for  example,  in  certain  parts  of 
the  sexual  organs.  It  matters  not  what  these  be  called,  whether  genital 
corpuscles  or  pleasure  end-organs,  the\\are  certainly  destined  to  incite 
to  the  function  to  which  they  are  attached  through  the  pleasure  they  or 
some  other  sort  of  entl-organs  give  rise  to.  If  at  the  same  time,  as  may 
well  be,  they  reflexly  actuate  the  varied  phenomena  of  coitus  and  ejacula- 
tion it  is  only  in  line  with  the  probable  action  of  other  various  sense- 
organs  throughout  the  body.  They  do  represent  pleasure,  and  pleasure 
as  a  true  sensation,  distinct  from  agreeable  or  pleasant  feelings. 

There  are  other  conditions  which  more  or  less  involve  various  sense- 
mechanisms.  Among  these  are  tickling  and  vertigo.  About  the  former 
little  worth  saying  can  be  given  in  this  place. 

Fig.  221 


Longitudinal  section  of   an  ampulla  of  the  fish  Gobius:    n,  nerve;   a,  canal;   b,  entrance 
into  the  common  chamber;   c,  epithelium;   d,  vibratable  "hair?."      (Hensen.) 


VERTIGO. 


This  sense  is  of  some  practical  importance.  It  arises  from  the  dis- 
turbance of  the  end-organ  of  the  vestibular  branch  of  the  eighth  cranial 
("auditory")  nerve.  This  end-organ  consists  of  the  semicircular 
canals,  the  ampullae,  and  part  of  the  labyrinth  connected  with  the  internal 
ear.  This  is  not  properly  a  sense-organ  in  the  sense  that  it  furnishes 
sensation,  for  no  consciousness  is  attached  to  its  action  unless  its  function 
(mostly  that  of  maintaining  reflexly  the  head's  eciuilibrium)  is  disturbed. 
In  proper  significance,  however,  that  a  sense-organ  is  a  peripheral  end- 
organ  of  an  afferent  nerve,  this  organ  is  a  true  sense-organ  and  vertigo  a 
sense.  Moreover  it  may  perhaps,  or  one  part  of  it,  have  to  do  with  the 
perception  of  noise,  as  we  have  seen  above. 
24 


370 


THE  SENSES 

Fig.  222 


Diagrammatic  cross-section  through  the  ampulla  of  a  semicircular  canal:  AM,  ampulla;  CR, 
acoustic?  crest;  CB,  basal  cells;  CS,  support-cells;  cc,  cuticle;  ca,  acoustic  (noise?)  cells  and 
their  hair-like  projections;   A'',  nerve-fiber  of  the  sound-cells.      (Duval.) 


FATIGUE,  THIRST,  AND  HUNGER. 

Fatigue,  thirst,  and  hunger  may  well  be  classed  together  as  the  most 
important  of  the  general  sensations.  They  each  have  an  unpleasant 
tone  and  well  illustrate  how  complex  the  sensations  may  be.  They 
arise  in  the  tissues  of  the  body  generally,  without  being  sensations  in  the 
physiological  sense  of  possessing  end-organs,  nerves,  and  cerebral  centers. 
Fatigue,  thirst,  and  hunger,  then,  are  on  the  border-line  between  physio- 
logical sensations  as  so  defined  and  the  host  of  psychophysiological 
feelings. 

Fatigue  in  its  origin  is  chiefly  either  muscular  or  neural:  our  "bodies" 
may  be  tired  or  our  "brains,"  or  both.  A  hard  day  at  trouting  in  some 
mountain  river  of  the  wilderness  is  apt  to  give  in  its  purity  the  sense- 
feeling  of  muscular  fatigue;  ten  hours' work  on  the  books  of  a  bank 
afiord  an  excellent  idea  of  what  is  meant  by  neural  fatigue;  while  a  day 
on  foot  at  a  world's  fair  would  combine  these  two  in  a  particularly  tiring 
way,  each  sort  lending  elements  of  intensity  to  the  oth(>r. 

In  di.scussing  briefly  the  bodily  aspect  of  the  feeling  of  fatigue,  one 
must  discriminate  it  in  the  first  place  sharply  from  exhaustion.  One  is 
physiological,  the  other  pathological.  The  former  may  be  recovered  from 
within  the  ordinary  periofls  of  rest,  but  the  latter  is  a  matter  of  incapacity 
for  days  in  the  case  of  muscles  or  for  many  months  at  times  (neuras- 
thenia) when  the  central  nervous  system  is  involved.  It  is  likely  too 
that  in  muscular  fatigue  actual  tearing  of  nerve-fibrils  has  taken  place, 
for  it  is  f|uite  abolishcfl  by  what  we  know  as  training  (Hough,  Wood- 
worth;.     By  this  means  the  organs  of  the  motor  apparatus,  muscular, 


FATIGUE,   THIRST,   AA'D  HUNGER  371 

neural,  and  vascular,  have  time  to  develop  by  growth  and  repair  to 
their  new  requirements.  In  neural  fatigue  the  changes  are  probably 
largely  metabolic  and  vascular,  while  in  nerve-exliaustion  the  shrinking 
of  the  nerve-cells  (as  Hodge  has  shown)  is  obvious  under  the  microscope. 
This  is  probably  of  far-reaching  import.  All  degrees  of  it  are  perceptible, 
some  arising  even  from  what  might  be  fairly  termed  normal  fatigue 
(see  Fig.  2G,  page  58). 

The  general  sensations  bring  out  the  difference  between  a  massive  or 
voluminous  sensation  of  low  intensity  and  a  special  sensation  which 
originates  in  the  functioning  of  a  single  sort  of  end-organ.  Compare 
the  feelings  caused  by  a  day's  long  climb  with  those  arising  in  an  un- 
trained finger  fatigued  on  one  of  the  ancient  Mosso  ergographs  so  com- 
mon in  the  laboratories.  The  latter  experience  is  mostly  a  localized  ache, 
the  former  a  wide-spread  general  sensation  of  low  intensity,  while  neither 
is  like  the  pain  caused  by  the  overstimulation  of  a  few  pain-organs  by 
part  of  the  red-hot  coal  of  a  parlor-match.  Widespread  stimulation 
to  their  limit  of  intensity  of  cutaneous  sense-organs  is  dangerous  to  life 
from  sheer  neural  shock.  It  appears  to  be  the  tissue-protoplasm  itself 
which  gives  the  feeling  of  fatigue.  To  attempt  therefore  to  trace  out 
nerves  or  nerve-centers  of  these  sensations  is  worse  than  useless,  because 
from  one  point  of  view  misleading.  For  fatigue  is  in  the  protoplasm 
of  the  muscles  mostly,  although  that  of  the  nervous  system  and  doubtless 
of  the  glandular  tissues  have  their  share.  (For  the  metabolic  changes 
occurring  in  muscular  action,  see  below,  page  3S2.) 

Thirst  is  also  a  general  sensation  (one  originating  all  over  the  body) 
dependent  on  a  decrease  in  the  fluidity  of  the  body-protoplasm  and  of 
the  circulating  lymph-plasma.  By  an  arrangement  whose  nature  is 
not  understood,  this  universal  need  is  referred  to  one  place,  the  throat 
and  mouth.  The  principle  here  as  elsewhere  is  that  the  protective 
sensation  is  felt  in  the  physiologically  right  place.  In  this  case  the  sensa- 
tion requires  that  the  water,  needed  all  over  the  organism,  shall  be 
placed  in  the  entrance  to  the  alimentary  canal,  for  from  this  organ  alone 
it  may  be  promptly  absorbed  into  the  circulation.  The  condition  is 
general  and  not  local,  for  it  may  be  promptly  relieved  by  injecting  water 
into  the  stomach  without  its  touching  the  mucosa  of  the  tongue  and 
pharynx,  as,  for  example,  through  a  gastric  fistula  made  for  feeding  the 
patient  in  cases  of  cancer  of  the  esophagus.  Again,  on  taking  the 
required  water  by  the  mouth  the  condition  is  not  relieved  as  the  liquid 
passes  over  the  tongue,  etc.,  but  only  after  the  twenty  seconds  or  so 
required  for  absorption  from  the  duodenum  into  the  blood  to  begin. 
The  sensation  may  have  perhaps  a  local  origin  besides  the  normal 
one  in  the  general  body-protoplasm.  Opium,  for  instance,  checks 
secretion  in  the  alimentary  mucosa,  as  do  many  other  substances,  while 
salt  dries  the  membranes  by  changing  their  osmotic  relations  to  the  blood 
and  lymph  within  them.  ^likl  inflammation  of  the  gastric  and  intestinal 
membranes  reflexly  produces  sometimes  the  sensation  of  thirst,  as  many 
persons  are  apt  to  know  the  morning  after  a  too  hearty  dinner. 


372  THE  SENSES 

The  afferent  nerves  concerned  in  the  sensation  of  thirst  are  evidently 
those  of  the  throat:  the  ninth  cranial  (glosso-phargngeal)  especially,  but 
also  probably  branches  of  the  tenth  (vagus)  and  the  fifth  (trigeminus). 

^Yater  is  by  far  the  best  liquid  for  relieving  thirst,  since  it  is  water  which 
forms  the  60  or  70  per  cent,  of  protoplasm.  Warm  water  relieves  it  as 
Cjuickly  as  cold,  but  affects  the  sensation  of  thirst  less  quickly  because  it 
lacks  the  coldness  which  so  promptly  relieves  the  mild  inflammation 
reflexly  begun  in  the  throat.  An  average  person  will  die  of  thirst  in 
four  or  five  days. 

Hunger  is  a  condition  similar  to  thirst  save  that  in  this  case  the  body's 
protoplasm  lacks  proteids,  carbohydrates,  fats,  and  inorganic  salts  instead 
of  water. 

The  experience  of  the  general  sensation  of  hunger  varies  with  the 
habits  of  the  person  as  regards  eating.  Many  accustomed  to  omit  their 
meals  or  food  entirely  for  a  day  or  even  two  at  a  time  fail  to  feel  the 
ordinary  phenomena  of  the  average  man  accustomed  to  go  without 
food  for  ten  hours  at  the  most  and  that  in  part  while  asleep.  Normal 
hunger  exhibits  a  feeling  of  weakness  plus  an  indescribable  sensation 
in  the  stomach  not  unpleasant  at  first  but  rapidly  increasing  to  a  "gnaw- 
ing" pain.  This  is  relievable  temporarily  by  taking  even  quite  indigesti- 
ble matter  into  the  stomach,  or  by  water.  After  two  or  three  days  the 
feeling  in  the  stomach  decreases  and  disappears  and  only  the  ever- 
increasing  feeling  of  weakness,  in  addition  to  the  other  bodily  phenomena 
of  inanition,  remains. 

What  causes  these  sensations  in  the  stomach  we  do  not  know.  They 
are  very  erratic,  sometimes  being  present  when  the  stomach  is  full  (as 
in  cases  of  duodenal  fistula),  and  on  the  other  hand  entirely  absent  when 
no  food  has  been  taken  for  days,  as  is  customary  in  gastritis,  for  example. 
Here,  then,  as  in  case  of  thirst,  we  have  a  general  sensation  normally 
referred  to  the  organ  where  the  demand  is  usually  supplied.  The 
stomach  is  really  no  hungrier  than  is  the  kidney,  yet  the  pain  is  in  the 
stomach,  for  here  the  means  of  relieving  it  are  needed.  In  this  case  the 
impulses  go  inward  along  the  tenth  cranial  (vagus)  nerve,  (the  chief 
sensor}^  nerve  of  the  stomach),  and  pass  to  the  almost  universally  con- 
nected roots  of  this  nerve  in  the  medulla  oblongata.  By  what  periph- 
eral organs  the  stimuli  are  started  toward  the  brain  we  do  not  know. 
In  most  normal  cases  distention  of  this  hollow  viscus  seems  to  provide  the 
opposite  sensation,  satiety. 

Xauska  is  another  general  sensation  referred  to  the  stomach,  but 
about  it  little  of  a  physiological  nature  is  known.  It  originates  from 
a  variety  of  causes.  It  comes  from  local  irritation  or  over-distention  of 
the  stomach  (csjK'cially  in  children),  and  from  stimulation  in  the  medulla 
or  cerebellum  (as  for,  example,  in  sea-sickness).  It  is  occasioned  l)y  the 
various  central  nauseants,  e.  r/.,  apomorphine,  and  by  many  other  drugs 
acting  locally  on  the  stomach  or  centrally  on  the  nerves.  (See  the 
descri})lion  of  vomiting,  p.  1S'(J.) 


CHAPTER    XL 


jniuscular  action. 


The  sense-orrans  which  we  have  iust  briefly  studied  are  at  the  begin- 
ning  of  the  typical  reflex  arc  in  the  nervous  system.  They  originate  the 
impulses  which  pass  into  the  cord  and  the  brain.  The  organs  which  we 
are  now  to  study  for  a  little  are  at  the  other  end  of  the  reflex  arc  and  are 
the  chief  means  by  which  the  individual  accomplishes  his  purposes. 
These  organs  are  the  muscles  found  in  nearly  all  parts  of  the  body. 
Homologous  to  them  as  active  instruments  are  the  glands,  and  these  we 
have  already  considered.  In  general  terms  the  function  of  the  muscles 
is  to  cause  the  approximation  of  two  parts  of  the  body  or  to  constrict  a 


Fig.  223 


Fig.  224 


Epithelio-muscular   cell 


muscular    prolongations 
(Dubois.) 


from    the    cell-body. 


A  diagram  suggesting  how  muscle-fibers 
originate:  a,  a  formative  cell  or  myoblast; 
b  and  c,  stages  in  development  of  contractile 
fibers  out  of  the  undifferentiated  protoplasm  in 
a  frog.      (R.  Hertwig.) 


hollow  tube  or  viscus.  Biological 
histology  deals  with  the  minute 
structure  of  various  contractile  or- 
gans, and  to  the  text-books  of  this 
science  the  reader  is  referred.  In 
some  of  the  simplest  animals,  even 
in  the  Protozoa  (for  example,  Sten- 
tor),  one  already  finds  contractile 
organs.  Here  they  are  in  the  form 
of  very  delicate  threads  technically 

called  myoids,  and  it  is  their  sole  lousiness  to  cause  the  animal  to  cjuickly 
shorten.  It  is  likely  that  something  very  similar  to  the  myoids  of  the 
simplest  animals  persists  in  all  muscular  tissue,  in  the  elaborately  evolved 
cross-striated  variety  as  well  as  in  smooth  muscle.  The  intimate  structure 
of  the  three  sorts  of  muscle  found  in  man  (cross-striated,  cardiac,  and 
smooth  muscle)  must  be  thoroughly  understood  in  connection  with  this 
chapter.  Knowledge  also  of  the  methods  of  grouping  of  the  contrac- 
tile cells  into  muscle-bundles,  of  those  within  the  anatomical  muscle,  and 


374 


MUSCULAR  ACTION 


of  the  relations  of  the  muscles  and  functional  groups  to  their  nerve- 
and  blood-supply  should  likewise  be  thoroughly  in  mind  before  the  study 
of  this  chapter  is  begun. 

Fio.  225 


Cilio-epithelio-muscular  filaments  of  the  parasite  Sagastia.      At  the  bottom  of  each  cell  one 
sees  the  part  most  like  the  smooth  muscle-fiber  of  man.      (Dubois.) 


Fig   226 


The  evolution  of  muscle:  o,  epithelio-muscular  cell;  b,  a  subepithelial  muscular  fiber;  c,  a 
longitudinal  muscular  fiber  (from  a  worm);  c,,  transverse  section  of  the  same;  e,  the  same  in  a 
bird;  d,  dorso-ventral  fiber  (from  a  marine  planarian);  /,  the  same  from  a  bird;  ff,  branched 
mu.scular  fibers  (^from  the  «(•]  of  a  otenopliore).      (Dubois.) 

The  Contractile  System  in  Man. — It  is  sometimes  ill-appreciated  how 
nearly  universal  in  the  organism  is  some  variety  or  other  of  contractile 
tissue — muscle.  There  are  more  than  four  hundred  more  or  less  inde- 
pendent muscles  classed  as  cross-striated  or  "voluntary,"  ranging  in 
size  from  the  vastus  extemus  to  the  stapedius  and  in  site  from  the  ends 


MUSCULAR  ACTION 


375 


of  the  toes  and  fingers  to  the  scalp.  Unstriated,  smooth,  or  "invoKintary" 
(reflex  or  "vegetative")  muscle  is  present  throughout  the  entire  vascular 
system  and  the  lymphatic  vessels,  placed  in  almost  exery  portion  of  the 
body;  in  the  wall  of  the  whole  alimentary  canal  from  the  pharynx  to  the 
anus;  in  the  gall-bladder  and  common  bile-duct;  in  the  trachea,  bronchi, 
and  bronchioles;  in  the  kidneys,  ureters,  bladder,  and  urethra;  in  the 
spleen;  in  the  adrenals;  in  many  gland-ducts  and  mucous  membranes;  in 


Fig.  227 


The  universality  of  muscle-tissue.  When  one  mentally  combines  the  fragmentary  views  shown 
here  and  extends  them  all  over  the  body  it  is  obvious  that  muscle  is  essentially  a  universal 
contractile  fabric  of  the  organism.      Functionally  it  is  not  merely  a  collection  of  separate  organs. 


the  skin;  in  the  sweat-glands;  in  the  mamma,  mammilla,  ovaries,  uterus. 
Fallopian  tubes,  vagina,  epididymis,  vas  deferens,  prostate,  tunica 
dartos,  seminal  vesicles;  in  the  iris;  and  probably  in  still  other  places. 
The  heart  is  made  largely  of  a  sort  of  muscle  partaking  of  the  nature 
apparently  of  both  these  other  sorts  of  muscle.  Van  Beneden  claims 
that  the  rays  of  the  amphiaster-spindle  in  mitosis  are  contractile  in  nature, 


376 


MUSCULAR  ACTION 


while  the  ciha  and  the  flagella  of  spermatozoa  are  certamly  so,  although 
not  classed  as  muscle.  Thus,  the  nervous  system,  epithelium,  the  skele- 
ton, certain  parts  of  the  sense-organs,  the  body-liquids,  and  the  epidermal 
structures  are  about  the  only  regions  (and  these  of  relatively  small 
volume)  in  which  muscle  of  some  sort  is  not  present.  INIuscle  is  the 
organ  or  tissue  of  gross  (as  distinct  from  molecular)  movement,  and  but 
few  indeed  of  the  active  organs  of  the  body  do  not  need  its  help.  Rather 
more  than  half  the  mass  of  the  adult  human  body  is  muscle,  and  this  is 
distributed  verv  widelv,  as  we  have  seen. 


Fig.  228 


Fig.  229 


A  muscle-cell  from  a  (nematode)  worm,  showing 
an  early  stage  of  diflferentiation.      (Glaus.) 


Lonsitudinal  partly  diagrammatic  section 
in  human  heart-mu.scle  to  show  especially  the 
bridges  of  contractile  tissue  extending  from 
one  cell  to  the  next.      (MacCallum.) 


The  Structure  of  Muscle. — Like  all  the  other  sorts  of  tissue  in  the  body, 
muscle  is  composed  of  protoplasm  arranged  (probably  because  of  the 
modes  of  producticm  and  reproduction)  in  cells.  In  the  cross-striated 
muscle-cells,  however,  difi'erentiati(jn  has  gone  very  far,  so  that  the 
cellular  plan,  if  we  think  of  an  average  epithelial  cell  as  the  type,  as  is 
commonly  done  cannot  very  readily  be  made  out.  In  the  smooth 
variety  of  muscle  and  in  that  of  the  heart  the  cellular  form  is  more 
apparent. 

We  may  divide  our  brief  descrij)tion  of  muscle  into  the  three  sorts 
above  mentioned:  smooth  or  "unstriated,"  cnj.ss-striated,  and  cardiac. 
It  .seems  likely  that  did  we  know  better  the  finer  structure  of  muscle  these 
sorts  would  in  part  be  found  to  merge  histologically  as  they  do  physio- 
logically, for  the  e.ssentia]  fibril  is  aj)parenlly  |)rcsent  in  all. 


MUSCULAR  ACTION 


377 


SirooTH  MUSCLE  is  made  up  of  fusiform  anisotropic  cells  ranging  in 
length  from  about  0.040  to  0.225  mm.,  and  in  width  from  0.004  to 
0.008  mm.  They  reach  their  known  maximum  size  in  the  uterus  in  its 
pregnant  state,  where  they  are  often  more  than  double  the  maximum  given 
above.  The  reticulated  nucleus  is  elliptical  and  is  placed  nearly  in  the 
middle  of  the  cell.  Striations  (myoids?)  are  clearly  to  be  made  out  run- 
ning the  entire  length  of  the  cell.     Those  about  the  periphery  of  the  cyto- 

FiG.  230 


€£< 


Smooth  muscle-fibers  of  the  uterus:    a,  from  a  virgin;   h.  from  a  pregnant  woman 

(Bumm.) 

plasm  are  relatively  coarse  and  straight,  while  within  they  are  finer  and 
constitute  a  distinct  reticulum.  Between  the  fibrils  is  the  homogeneous 
and  transparent  sarcoplasm.  The  cells  are  collected  together  in  spindle- 
shaped  bundles,  each  bundle  being  enclosed  in  a  delicate  fenestrated 
membrane  (as  is  also  each  cell)  called  its  sarcolemma.  The  meaning 
of  the  oval  openings  in  this  membranous  bundle-covering  is  not  yet  clear. 
Several  histologists  have  described  fine  protoplasmic  bridges  connecting 
the  sarcoplasm  of  the  cells  in  the  bundle,  but  these  have  lieen  declared 


378 


MUSCULAR  ACTION 


artifacts  by  others,  and  hence  the  matter,  so  important  for  the  physi- 
ology of  muscle,  must  be  a  little  lonojer  considered  in  doubt.  The  free 
transmission  of  the  contraction-wave,  for  example,  in  hollow  organs  like 
the  ureters,  makes  probaVjle  some  such  mode  of  connection  between  the 


Fig.  231 


The  smooth  muscle  in  the  bronchioles  of  the  dove's  lung.      (Eberth.) 

various  cells  and  bundles  whether  the  staining  methods  at  present. in 
use  show  such  connections  clearly  or  not.  Each  fiber-cell  is  surrounded 
by  a  very  delicate  transparent  sheath  which  wrinkles  more  or  less  when 
the  fiber  changes  its  shape  in  contracting. 

Cross-striated  muscle  is  the  variety  most  fully  under  the  will's 
control,  and  it  is  therefore  often  called  voluntary  muscle ;  it  is  frequently 
attached  to  the  bones  and  hence  is  sometimes  termed  skeletal  muscle. 


Fig. 


Nucleus- ^ir.- 


Intercelliil'i 
hridij' 


<&i  ■ 


Longitudinal  section  in  the  smooth  muscle  of  a  dog's  \:uv.<-  infistine,  to  show  especially  the 
intercellular  bridges,      ^'"/i-      (Szymonowicz  and  MacCallum.) 


Cross-striated  mu.scle,  like  the  smooth  sort,  is  made  up  of  fusiform 
cells.  These  are,  however,  apparently  of  much  greater  structural  com- 
plexity and  differ  much  from  the  others  in  size  and  mode  of  action.  The 
fibers  or  cells  (each  fiber  being  apparently  a  highly  specialized  cell),  of 
cro.ss-striated  muscle,  are  more  or  less  cylindrical  in  shape.  In  size  they 
may  be  even  as  much  as  12  cm.  long  and  0.1  wide,  and  they  are  thicker 
in  the  male  than  in  the  female.     Roughly  speaking,  the  fibers  are  smaller 


MUSCULAR  ACTION 


379 


in  the  more  finely  adjustable  muscles  (such  as  those  of  the  eye)  than  in 
the  coarser  muscles  (like  the  glutei,  for  example).     ^lost  of  the  fibers  in 


Fig.  233 


The  anastomosis  of  muscle-bundles  as  found  in  the  urinary  bladder  of  the  cat. 
nerve-cells  and  -fibers  are  to  be  seen  between  two  of  the  muscle-bundles. 


Intermuscular 
(Metzner.) 


Fig.  234 


Nucleus 


Primitive  fihril 


Vmi  liUs<\iH{\l III 


/i/iiiinuMni?»i!| 

U  iiiiiiiiiiiiiiOiil 

•  JLniiiiifih'ritn.q 
[! iiiiiu  I  if  i»"i.'i 


.Transverse  line  of  Briicke 


Krnuse's  memhrnne 


C^ 


A  bit  of  a  cross-striated  muscle  of  a  frog,  showing  the  nucleus  and  the  ease  of  its  division 
both  transversely  and  longitudinally,     '^"/j.     (Szymonowicz  and  MacCullum.) 


3S0 


MUSCULAR  ACTION 


man  are  not  more  than  4  cm.  long.  The  fiber  usually  ends  in  its  ten- 
don in  a  quickly  tapering  single  point,  but  where  a  layer  of  tissue  such  as 
the  skin  is  to  be  moved,  and  in  the  tongue,  the  fibers  branch  repeatedly. 
About  the  fiber  is  a  sarcolemma,  a  thin,  transparent,  and  tough  elastic 
membrane  best  seen  when  the  enclosed  fiber  is  torn  apart.  The  muscle- 
substance  itself  is  elaborately  composed  of  units  whose  exact  status  is 
not  yet  clear.  The  regular  arrangement  of  these  units  (called  by  Schafer 
sarcomeres)  is  such  that  under  the  microscope  the  fiber  seems  striated 
both  transversely  and  longitudinally.     A  section  of  units  transversely 


Fig.  235 


Fig.  236 


Across-striated  mu.scle-fiber  from  the  epi- 
physis cerebri  (pineal  gland;  of  the  ox. 
(Dimitrova.) 


Tlie  capillary  network  of  cros.s-striated  mus- 
cle: a,  arteriole;  h,  veinlet;  c  and  d,  the  retic- 
ulum of  cai)illarie.s.      (v.  Frey.) 


divided  constitutes  a  disk  (such  as  Schafer  shows  from  a  beetle's  leg- 
muscle)  but  longitudinally  considered  it  is  a  fihril  or  sarcostyle  extending 
the  length  of  the  fiber  or  cell.  Each  of  these  transverse  disks  is 
usually  about  1.5  microns  thick  when  a  muscle  is  moderately  extended, 
but  sometimes  not  more  than  half  of  that.  The  sarcostyles  or  fibrils, 
each  consisting  of  a  row  of  prismatic  sarcomeres  or  sarcous  elements,  are 
separated  from  each  f)ther  in  the  fiber  by  a  small  amount  of  transparent 
.substance  called  .sarc()j)lasm.  The  fibrils  or  .sarcostyles  are  in  turn 
made  up  of  fibrils,  and  by  some  writers  unfortunately  it  is  these  which 


MUSCULAR  ACTION 


381 


are  termed  sarcostyles.  Cross-striated  muscle  is  well  named,  therefore, 
for  numerous  striations  in  both  directions  divide  the  protoplasm  into 
many  sorts  of  minute  cubical  compartments  or  units  whose  respective 
significance  is  not  yet  made  out  either  structurally  or  functionally. 
The  histology  of  muscle  is  still  further  complicated  l^y  the  complex 
optical  properties  of  the  substance,  so  that  the  appearances  under  one 
set  of  conditions  are  quite  unlike  those  in  the  same  structure  under 
another  set,  while  preservmg  and  staining  methods  produce  very  vari- 
ous effects.  It  is  possible,  as  MacCallum  suggests,  that  the  optical 
appearance  of  this  sort  of  muscle  is  partly  due  to  a  reticulum  with  regu- 
lar meshes  extending  through  the  protoplasm,  of  which,  the  ultimate 
fibrils  and  Krause's  membrane,  so  called,  are  the  chief  elements.  (See 
Fig.  278  page  499.) 

According  to  a  common  notion,  in  the  middle  of  each  of  these  sarcomeric 
parts,  and  transversely  across  it,  is  Krause's  "membrane;"  on  either  side 
of  it  an   intermediary  disk  of  clear  isotropic  substance  (sarcoplasm  or 


Fig.  237 


...F 


Cross-section  in  human   heart-muscle,  above 

or  else    below    the  nucleus:  C,    central  sarco- 

plasm-mass;     <S,    sarcoplasmic   disk;     F,  fibril- 
bundle.      (MacCallum.) 


Longitudinal  section  in  human  heart-muscle: 
S,  sarcoplasmic  disks;  F,  fibril-bundle;  K, 
Krause's  membrane.      (MacCallum.) 


lymph);  next  a  broad  dark  band  which  is  bisected  by  Hensen's  median 
(light)  disk,  and  finally  this  in  turn  by  the  median  (dark)  disk  of  Heiden- 
hain.  Krause's  "membrane"  appears  to  extend  across  the  fiber  and  to 
be  continuous  with  the  sarcolemma.  An  observation  chance  made  by 
Kiihne  seems  to  place  the  consistence  of  the  crossing-structures  still 
more  in  doubt  than  before.  If  really  membranous,  Krause's  "mem- 
brane" is  of  only  slightly  greater  consistence  than  its  surroundings. 

It  is  rather  more  than  possible  that  the  individual  fibers  are  connected 
by  some  sort  or  other  of  bridges  made  of  muscular  tissue. 

The  nuclei  of  the  cells  of  striated  muscles  of  man  are  mostly  just  within 
the  sarcolemma,  but  sometimes,  as  in  the  red  sort  oi  rabbit-muscle,  deep 
within  the  fiber-cell.  About  the  nuclei  is  often  a  more  or  less  granular 
substance. 

The  vascular  and  nervous  service  of  muscle  is  verv  al^undant,  the 


382  MUSCULAR  ACTION 

blood-vessels  being  large  and  numerous  and  intimately  distributed,  and 
the  nerves  of  large  size  and  much  complexity  of  course  and  endings. 
L}Tnphatics  are  abundant  in  the  connective-tissue  coverings  of  the 
different  muscular  parts,but  do  not,  anymore  than  do  the  blood-vessels, 
extend  mto  the  cells,  apparently.  (For  the  nerve-endings  of  muscle,  see 
the  preceding  chapter,  page  329.) 

Cardiac  muscle  is  striated  in  both  directions,  but  always  less  dis- 
tinctly than  is  cross-striated  muscle.  Another  leading  characteristic  is 
the  relatively  large  amount  of  sarcoplasm,  as  may  be  seen  in  Figs.  237 
and  238,  by  MacCallum.  Moreover,  the  morphological  units  (cells)  are 
closely  connected  in  such  a  way  as  to  appear  branched,  combining  in 
this  way  to  constitute  a  coarse  striated  network  made  up  of  sarcostyles, 
which  in  turn  are  strings  of  sarcomeres.  No  thick  sarcolemma,  it  is  said 
by  some  observers,  appears,  but  the  sarcostyles  have  sheaths.  There 
may  be  three  or  four  nuclei  in  each  cell ;  they  are  oval  in  shape  with 
distinct  chromatin  reticulum  and  surrounded  (as  in  skeletal  muscle)  with 
granular  protoplasm  whose  granules  increase  with  the  individual's  age. 
Ultimate  fibrils  compose  the  sarcostyles  as  in  other  sorts  of  muscle  and 
pass  uninterruptedly  from  one  morphological  cell  to  the  next. 

The  importance  of  an  extension  of  our  knowledge  of  cardiac  muscle 
for  therapeutic  reasons  cannot  easily  be  over-estimated,  the  saving  of 
many  lives  lying  in  this  direction  of  reasearch. 

The  Chemistry  of  Muscle. — ^This  subject  is  of  importance  because  the 
muscles,  by  their  metabolism,  furnish  a  large  part  of  the  energy  and  of 
the  heat  of  the  body,  and,  furthermore,  because  it  underlies  the  mode  of 
working  of  the  muscle. 

In  crude  and  general  terms  human  muscle  is:  water,  73  per  cent.; 
proteids,  19  per  cent.,  fats,  2  per  cent.;  "inorganic"  salts,  2  per  cent.; 
and  chemical  sundries,  4  per  cent.,  these  latter  being  mostly  carbohy- 
drates, purin  bodies,  and  gelatin.  It  is  not  obvious  that  the  water  of 
the  muscle  is  concerned  in  the  actual  metabolism  of  the  tissue,  but,  as 
we  have  already  pointed  out,  it  is  essential  to  the  active  movement  of 
these,  as  of  all  other  organs.  The  proteids  of  dead  muscle  may  not  be 
those  of  living  muscle,  but  of  the  former  we  know  only  a  little,  and  of  the 
latter  nothing.  There  are  two  proteids  probably  peculiar  to  muscle: 
the  globulin,  called  para-myosinogen  (called  myosin  by  Fiirth),  and 
myosinogen.  These  two  proteids  become  myosin  under  many  condi- 
tions, this  process  being  probably,  for  example,  at  the  basis  of  ricjor 
mortis.  Dubois  suggests  an  instructive  formula  by  which  the  katabolism 
of  albumin  might  conceivably  be  conducted,  and  it  is  reproduced  here 
chiefly  as  a  sort  of  chemical  diagram,  infinitely  simpler,  of  course,  than 
the  reality,  and  useful  chiefly  as  a  list  of  the  products  named. 

CjjHijjXjgSOj^.  albumin  +  20(H.2O),  water  = 
7(C0X,H,),  urea 
+  ofCfiHu.Oj),  filycopen 
+  C.^,H4eO,  cliolcsterin 
+  ;^rC,H5N0,),  glvcocoll 
+  r,H.NSO.„  taurin 
+  (ill,  liy<lrof;en 


MUSCULAR  ACTlOy  383 

It  is  in  part  the  goal  of   biochemistry  and  of  chemical   physiology  to 
replace  this  possible  outline  with  the  actual  formula  in  all  its  details. 

Carbohydrates  are  present  in  muscle  only  in  a  small  percentage,  as 
we  have  seen,  but  their  importance  in  the  metabolism  of  this  tissue  is 
apparently  great.  The  two  chief  carbohydrates  present  are  glycogen 
and,  in  much  smaller  proportion,  dextrose.  The  former,  glycogen, 
present  in  most  animal  tissues,  if  not  all,  is  doubtless  the  chief  source 
of  muscular  energy.  Manche  found  that  a  limb  made  to  contract  for 
about  an  hour  showed  about  14  per  cent,  less  glycogen  than  the  corre- 
sponding resting  limb,  and  that  ligation  of  the  arteries  produced  a  like 
result.  In  starvation  the  glycogen  rapidly  disappears  from  the  muscle. 
In  muscular  paralysis,  whatever  its  cause,  glycogen  accumulates  in  this 
tissue.  Most  abundant  of  the  elements  in  the  inorganic  salts  of  muscle 
are  potassium  (which  is  preponderant),  sodium,  calcium,  magnesium, 
chlorine,  sulphur,  and  phosphorus,  the  three  last  being  represented  as 
the  chlorides,  sulphates,  and  phosphates  of  the  others.  It  is  a  striking 
fact  that  a  muscle  does  not  contract  spontaneously  in  aqueous  solutions 
containing  no  ions,  for  example,  in  a  distilled-water  solution  of  chemically 
pure  cane-sugar.  The  large  amount  of  research  which  has  recently 
been  made  into  the  relations  of  muscular  activity  and  inorganic  salts  is 
left  to  tell  us  what  chemism  and  electricity  have  to  do  with  muscular 
action.  Urea,  creatin,  creatinin,  xanthin,  hypoxanthin,  and  carnin  are 
found  in  muscle,  as  well  as  many  other  nuclein  bases.  Just  how  these 
substances  are  produced  in  the  katabolism  of  muscle  it  is  impossible  at 
present  to  say. 

The  Modes  of  Action  of  Muscle. — It  is  one  thing  to  understand  the  struc- 
ture and  composition  of  a  complicated  mechanism,  but  quite  another 
sometimes  to  know  exactly  how  it  works.  In  the  case  of  muscle  this 
problem  is  made  worse  by  the  minuteness  of  the  structures  and  by  the 
intricacy  of  the  physics  concerned  in  the  action  of  this  highly  differ- 
entiated kind  of  protoplasm.  As  yet  we  cannot  tell  how  muscle  develops 
its  contractile  energy,  so  the  best  we  can  do  is  to  describe  summarily  a 
few  of  the  various  theories  as  to  the  matter.  Our  immediate  problem 
is,  then,  as  to  exactly  how  and  why  the  fibrils  of  muscle  shorten  and 
thicken  and  then  immediately  lengthen  and  attenuate  again.  Do  cross- 
striated  and  smooth  muscle  act  in  the  same  way?  (See  also  page  487.) 
We  can  go  a  certain  way  on  relatively  solid  ground.  We  know  the 
probable  structure  of  cross-striated  muscle,  substantially,  so  far,  at  least, 
as  appearances  go.  We  know  that  it  consists  of  two  sorts  of  substances, 
one  (anisotropic)  doubly  refracting  polarized  light,  the  other  (isotropic) 
refracting  it  singly.  We  know  that  when  the  contraction  occurs  in 
cross-striated  muscle  the  latter  kind  of  material  changes  its  place  some- 
what, while  the  former  kind  does  not  do  so.  We  are  sure  that  the 
metabolism  of  all  sorts  of  muscle  is,  in  part,  the  oxidation  of  carbo- 
hydrates and  of  protein,  sarcolactic  acid  being  a  way-product,  and 
carbon  dioxide  and  water  among  the  end-products.  The  more  active 
the  contraction  of  the  muscle  the  more  oxvofen  it  consumes  and  the 


384  MUSCULAR  ACTION 

more  carbon  dioxide  is  liberated  from  it.  We  know  that,  as  often 
happens  in  protoplasm,  the  chemism  of  metabolism  gives  rise  to  at  least 
three  sorts  of  kinetic  energy:  movement,  heat,  and  electricity,  for  these 
may  be  measured  and  variously  studied. 

If  we  start  out  with  the  fact  that  it  is  chemism  undoubtedly  which 
liberates  these  energies,  we  have  the  basis  of  the  chief  various  theories 
of  muscle-action.  To  one  (Engelmann)  it  seems  clear  enough  that 
the  chemism  gives  rise  to  heat,  which,  by  causing  imbibition  of  sarco- 
plasm,  brings  about  the  contraction.  Another  "school"  (Pfliiger, 
Bernstein,  Verworn,  Fick)  supposes  that  the  chemism  directly,  i.  e., 
without  the  intervention  of  heat,  alters  the  two  differing  substances  in 
such  a  way  that  the  isotropic  one  swells  into  the  anisotropic.  A  recent 
group  of  thinkers  (Miiller,  Loeb)  suppose  that  electricity  is  involved  in 
causing  the  contraction.  To  others  (e.  g.,  Weber),  the  chemism  seems 
to  alter  the  natural  elasticity  of  the  myoids  or  fibrils,  making  them 
shorten  and  then  lengthen.  Numerous  other  hypotheses  still  less 
probable  have  been  published  at  various  times. 

The  Ther:mo-dynamic  Theory. — ^The  thermo-dynamic  theory  just 
now  seems  perhaps  more  satisfactory  than  any  other.  By  means  of  a 
coil  of  platinum  wire  surrounding  a  short  string  of  catgut  kept  warm  in 
a  proper  solution,  Engelmann  demonstrated  that  this  form  of  proto- 
plasm at  least  shortens  when  heat  is  applied  to  it  (the  heat  was  produced 
by  sending  an  electric  current  through  the  platinum  wire).  Rubber 
behaves  essentially  in  the  same  way.  The  curve  made  on  a  rotating 
smoked  drum  by  both  of  these  substances  under  these  conditions  is 
much  like  that  traced  by  a  contracting  gastrocnemius  of  the  frog  (see 
p.  473  of  the  Appendix).  This  experiment  was  at  the  basis  of  Engel- 
mann's  thermochTiamic  theory.  His  supposition,  in  fine,  then,  is  that 
metabolism  (probably  the  katabolism)  of  carbohydrates  causes  a  liber- 
ation of  heat  in  or  about  the  myoids  of  muscle,  and  so  causes  them  to 
shorten.  The  main  objections  raised  to  this  theory  amount  to  an 
assertion  (as,  for  example,  by  Fick)  that  the  heat-increase  which  actually 
obtains  in  a  contracting  muscle  is  not  sufficient  to  produce  the  effects 
observed.  In  answering  this,  Engelmann  suggests  a  rather  far-reaching 
principle,  useful,  perhaps,  in  more  than  this  one  place:  the  temperature 
of  some  of  the  chemically  acting  individual  particles  in  a  muscle  might 
increase  many  degrees  and  yet  not  raise  the  temperature  of  the  muscle- 
mass  (two-thirds  \\'atei-j  more  than  a  thousandth  of  a  degree.  At  the 
.same  time  the  heat  rapidly  produced  l)y  means  of  these  relatively  few 
metabolizing  particles  might  very  well  cause  the  muscle  to  contract.  In 
general  terms,  that  which  takes  place  in  an  ultra-microscopic  group  of 
molecules  may  be  very  different  from  what  our  relatively  gross  instru- 
ments allow  us  to  observe  in  an  organ  as  a  whole. 

On  the  basis  of  this  rapid  heating  and  cooling  of  minute  metabolic 
parts  of  a  muscle  the  next  supposition  of  the  thermodynamic  theory  is 
that  this  heating  of  the  segments  of  the  myoids  or  sarcostyles  causes  the 
liquid  of  the  isotropic  (light-ljanded)  segments  of  the  sarcomere  to  be 


MUSCULAR  ACTION 


385 


absorbed  by  the  dark  or  anisotropic  disks.  The  lymph  or  sarcoplasm 
flows  in  at  Hensen's  Une  and  then  in  the  two  opposite  directi(jns  of 
Krause's  "membranes."  The  work  of  Schiifer,  histological  in  nature, 
tends  to  corroborate  the  suppositions  of  Engelmann  and  to  make  this 


Fig.  239 


Relaxation 

Anaboli'Sm. 
Glycogen 


Contraction. 
Katabol/sm. 
Oxygen. 


Dextrose,  etc. 


Carbon  dioxide, 

yyater. 

Lactic  Acid,  etc. 


iSpong/oplasm, 
Sarcoplasm. 


Thermic  pdrtides  o/       •       ^ 
caj-jbohydrcLte.        *   *    •      • 


Muscular  action  according  to  the  Engelmann-Schafer  theory  of  plasniic  imbibition 
caused  by  heat. 

theory  of  sarcomeric  imbibition  of  muscle-plasm  more  prol)able  than  any 
other.  Blindly  ending  canals  seem  to  Schafer  to  constitute  the  essen- 
tial part  of  the  minute  sarcomeres,  these  swelling  outward  laterally  and 
shortening  as  they  fill  with  the  muscle-lymph  from  the  isotropic  disks. 
25 


3S6  MUSCULAR  ACTION 

If  these  suppositions  are  true,  there  remains  to  be  worked  out  the  ther- 
mogenic metaboHsm  and  also  the  spatial  relations  of  the  heating  particles 
to  the  structural  elements  of  the  sarcostyles.  (See  Fig.  239.)  On  what 
basis  to  adapt  this  working-hypothesis  to  smooth,  "unstriated"  muscle 
is  not  apparent.  Little  or  nothing  is  kno^^^l  about  the  finer  structure 
of  the  myoids  and  muscle-fibrils,  and  this  ignorance  makes  application 
of  so  elaborate  a  theory  out  of  the  question  at  present. 

On  the  whole,  then,  the  thermogenic  theory  of  sarcomeric  imbibition 
cannot  be  said  to  be  wholly  satisfactory;  but  it  is,  perhaps,  the  best  so 
far  devised. 

The  Chemi-surface-tension  Theory. — The  chemi-surface-tension 
theory  has  been  of  late  perhaps  better  championed  by  Verworn  than  by 
others.  This  theory,  as  set  forth  especially  by  him,  has  already  been 
given  briefly  in  the  chapter  on  protoplasm,  but  purely  from  the  point  of 
view  of  undifferentiated  protoplasm.  Surface-tension  is  the  cause  of 
the  tendency  to  surface-contraction  characteristic  of  liquids.  It  is  this 
force,  for  example,  which  makes  a  drop  of  dew  on  a  leaf  spherical  instead 
of  flat.  It  is  a  potential  energy  of  cohesion,  apparent  y,  between  the 
adjacent  molecules  at  the  bounds  of  a  mass  of  liquid. 

Perhaps  we  could  not  do  better  justice  to  this  theory  of  muscular  con- 
traction than  to  state  it  in  the  terms  of  Verworn:  "During  the  explo- 
sive decomposition  of  the  biogens  [protoplasmic  units]  either  in  the  iso- 
tropic or  the  anisotropic  substance  (which  latter  is  regarded  by  Engel- 
mann  as  the  specially  contractile  element),  the  chemical  constitution  of 
the  biogen-molecules  is  so  changed  that  a  molecular  attraction  arises 
between  them  and  certain  constituents  of  the  other  substance.  As  a 
result  of  this,  the  surface-tension  between  the  two  disks  (the  sarcomeres) 
must  necessarily  diminish  (or  even  become  zero),  i.  e.,  an  intermingling, 
a  mutual  penetration  of  the  two  substances  must  take  place.  In  this 
process  the  isotropic,  as  the  more  mobile,  substance  will  necessarily 
diffuse  into  the  anisotropic,  as  the  more  fixed,  i.  e.,  the  muscle-segment 
will  necessarily  decrease  in  length  and  increase  in  breadth.  There  will 
thus  be  in  principle  the  same  process  as  in  swelling,  except  that,  as 
Engelmann  assumes,  there  will  be  not  a  simple  admission  of  water,  but 
a  chemical  swelling,  in  which  along  with  the  water  other  chemical 
substances  will  enter,  such  as  take  part  in  the  regeneration  of  the  decom- 
posed biogen-molecules.  But  in  proportion  as  these  molecules  are 
regenerated  and  by  the  introduction  of  oxygen  are  brought  back  to  the 
maximum  of  their  labile  constitution,  a  change  in  the  molecular  rela- 
tions occurs,  and  now,  in  contrast  to  what  happened  previously,  a  separa- 
tion of  the  two  substances  will  take  place,  whicli  will  give  to  the  muscle- 
segment  its  original  form. 

"Although  the  processes,  which  for  tiie  present  are  wholly  unknown, 
may  in  reality  take  place  very  differently,  at  all  events  the  principle  of 
modification  of  the  molecular  attraction  by  changes  in  the  chemical 
constitutifm  of  the  molecules,  the  same  principle  that  explains  ameboid 
movement,  appears  to  be  able  to  elucidate  in  its  essential  points  the 


MUSCULAR  ACTION 


387 


obscure  plienomena  of  muscular  movement.  Thus,  contraction-move- 
ments in  their  most  essential  points  are  controlled  by  the  direct  inter- 
changes of  chemical  and  meclianical  energy  without  the  mediation  of 
another  form  of  energy,  such  as  heat  or  electricity." 

It  is  to  be  noted  that  according  to  this  theory  the  most  essential  process 
preliminary  to  relaxation  is  the  absorption  of  oxygen  and  oxidation. 
This  soon  would  cause,  we  might  suppose  (from  analogy  with  ameboid 
movement),  a  loosening  of  the  surface-molecules  of  the  sarcomeres,  a 
lessening  of  surface  tension,  and  a  flowing-backward  of  the  liquid  sar- 
coplasm  into  the  isotropic  sarcomeres,  lengthening  and  attenuating  the 
sarcostyles  or  fibrils  to  the  uncontracted  condition.  Contraction  thus 
is    katabolic,  oxygen   being  absorbed;   relaxation  is  anabolic,  oxygen 


Fig.  240 


TM 


Four  types  of  arrangement  of  the  muscle-fibers  of  skeletal  muscles:  M,  belly  of  muscle;  T,  T', 
tendons  of  origin  and  insertion;  a,  b,  length  of  muscular  belly.  It  is  obvious  that  in  a  muscle 
short  fibers  usually  mean  small  but  powerful  movement,  while  long  fibers  bring  about  consider- 
able movement  of  relatively  little  force.  Compare,  e.  g.,  the  gastrocnemius  (type  D)  with  the 
sartorius  (type  A).      (Beaunis  and  Bouchard  via  Gray.) 

passing  out  as  part  of  the  carbon  dioxide  excreted  from  all  protoplasm. 
The  two  phases  are  interdependent  parts  of  one  rhythmic  function. 

Other  theories  of  muscular  contraction  we  have  here  no  reason  to 
discuss,  for  the  evidence  for  them  seems  at  present  less  than  for  the  two 
theories  already  outlined. 

When  the  complexity  of  the  protoplasmic  metabolism  and  the  minute- 
ness of  the  muscular  structure  is  considered,  the  details  of  which  are  as 
yet  largely  unkno^Ti,  it  is  not  strange  that  the  precise  method  by  which 
muscle  works  is  not  yet  learned. 

The  Neuro-muscular  Mechanism  has  been  already  described  in  part  in 
this  book — the  nerve-centers  and  nerve-paths  in  the  chapter  on  the  Ner- 
vous System,  and  the  kinesthetic  sense-organs,  etc.,  in  the  discussion  of 


3S8  MUSCULAR  ACTION 

the  senses.  It  remains  here  to  look  at  this  muscular  coordination  and 
control  mostly  from  the  side  of  the  muscles.     (See  Fig.  ISS,  p.  334.) 

It  has  been  emphasized  that  the  nerves  form  with  the  muscles  (and 
glands  and  sense-organs)  a  functional  wiiiy  if  not  a  complete  structural 
continuum  of  protoplasm,  a  principle  of  importance  in  the  theory  of 
muscular  control.  Philosophically  one  has  to  consider  the  nerve- 
muscle  group  of  organs  as  agent  of  the  individual  will  ready  at  all  times 
to  bring  about  whatever  movement  the  biological  needs  of  the  animal 
demand.  It  is  only  by  the  intimate  union  of  the  nervous  system  with  the 
muscle  system,  reaching  thereby  nearly  every  body-cell,  that  the  muscles 
are  made  almost  the  universal  instrument  of  every  function  in  one  way 
and  degree  or  another.  In  other  words,  the  all-pervading  "nerve-net" 
brings,  perhaps,  into  the  immediate  service  of  every  part  of  the  body 
practically  the  whole  muscle-mechanism. 

The  relations  of  voluntary  movement  to  reflex  movement  were  dis- 
cussed in  the  chapter  on  the  Nervous  System.  It  is  largely  a  matter  of 
habit,  of  repetition  until  the  action  is  on  a  mechanical  basis  almost,  that 
finally  turns  a  laborious  new  voluntary  movement,  made  only  at  first  by 
exercise  of  perhaps  strained  attention,  into  a  reflex  group  of  movements 
nearly  free  of  mental  effort.  The  muscles  in  unity  with  the  nerve-net 
learn,  acquire  readiness  and  coordinated  accuracy,  what,  in  short,  is 
knouTi  as  skill  or,  more  broadly  looking,  cleverness.  What  is  the  mus- 
cular side  of  the  development  of  this  capacity,  one  of  the  most  precious 
of  man's  powers,  one  of  the  largest  elements  in  the  evolution  of  his 
civilization  and  culture  ?  While,  indeed,  "the  reign  of  the  brain  is  plain,'' 
it  is  easy  to  limit  too  closely  what  we  mean  by  "brain"  and  to  forget  that 
the  nervous  system  is  above  all  a  system  of  conducting  paths.  These  are 
so  infinitely  devious  that  in  a  sense  they  form  a  net,  and  yet  they  are 
useless  without  something  to  connect,  without  some  way  of  expressing 
in  the  material,  practical  world  that  system  of  adjustments  which  com- 
bined are  life.  The  most  immediate  agent  in  this  direction  is  the  mus- 
cular system.  How  then  does  a  musculature  learn?  and  in  learning, 
what  development  does  it  undergo? 

There  are  two  directions  in  which  a  muscle  may  develop:  vigor  and 
strength,  and  skill  or  delicacy  of  adjustment.  The  latter,  skill,  involves 
a  degree  of  the  former,  vigor,  but,  on  the  other  hand,  the  vigor  may  be 
present  with  little  delicacy  of  coordination.  To  some  extent,  indeed,  in 
their  higher  degi-ees  these  are  opposed  and  in  practice  rarely  present  in 
the  same  muscle-group.  The  strong-man  in  the  circus  is  seldom  a  grace- 
ful dancer,  and  the  expert  engraver  or  musician  is  only  rarely  an  athlete. 
The  reason  for  this  lies  largely  in  the  fact  that  the  time  rcfjuired  for  one 
sort  f)f  flevclopmciit  excludes  development  of  the  other  kind;  but  there  is 
a  true  physiological  opposition  of  a  certain  degree.  In  athletic  training 
the  endeavor  is  constantly  to  overcome  this  oj)j)ositi()n,  to  acquire  skill 
in  playing  combined  with  a  large  degree  of  strength.  The  games  in 
which  both  mean  mufh,  such  as  tennis,  golf,  rowing,  or  base-ball,  are 
then  theoretically  the  l)est  for  the  general  good  oi'  tiie  organism. 


MUSCULAR  ACTION  389 

In  developing  strength  the  muscles  and  their  nutrition  are  almost 
solely  concerned,  although  the  exercise  involved  indirectly  tends  to 
develop  all  parts  of  the  body  (see  below).  It  is  not  easy  to  find  any  data 
of  a  precise  histological  nature  on  the  effects  of  long-continued  exercise 
or  work  on  the  muscle-fiber  itself,  either  smooth  or  cross-striated,  but 
the  effects  on  a  muscle  in  general  are  fairly  well  known.  In  the  first 
place,  when  a  muscle  by  working  becomes  stronger,  it  grows  somewhat 
larger,  and  this  notwithstanding  that  the  thin  layers  of  fat  within  the 
muscle  are  oxidized  and  disappear.  The  muscle-fibers  probably  in- 
crease not  only  in  number  but  in  size  as  well.  A  second  condition  obvious 
in  a  strong  muscle  (and  a  better  strength-index  than  size)  is  hardness  or 
tone  together  with  an  increase  of  elasticity.  The  growth  of  the  fiber 
distends  more  fully  the  sarcolemma  and  that  of  the  fiber-bundles  their 
coverings  of  fascia.  In  an  abundantly  fed  muscle  the  elasticity  is  greater 
than  in  one  poorly  fed.  A  fourth  change  which  takes  place  as  a  muscle 
strengthens  is  a  marked  increase  in  the  collagen  coverings  (sarcolemma, 
fascia,  aponeurosis,  etc.)  of  the  muscle-bundles.  These  membranes 
are  very  strong  and  elastic,  for  their  function  is  to  keep  in  place  the  muscle- 
fibers  and  muscle-bundles  which  are  more  than  half  liquid,  allowing  them 
at  the  same  time  to  glide  with  little  friction  over  or  within  each  other.  In 
a  poorly  nourished  man,  especially  if  at  the  same  time  his  muscle  be 
overworked,  these  coverings  are  especially  prominent,  developing  out  of 
proportion  to  the  protein  muscle-fibers.  This  consideration  has  a 
bearing  on  the  contention  of  Chittenden  that  most  men  eat  far  too  much 
protein,  being  against  the  supposition  as  applied  to  those  who  do  much 
muscular  work.  A  fifth  but  accessory  change  in  a  hard-worked  muscle 
is  a  development  of  the  blood-vessels  to  allow  of  a  freer  nutritional  supply 
and  excretion.  There  is  a  corresponding  new-growth  of  nerve-fibrils 
which  more  than  replaces  those  lost  by  metabolic  and  mechanical  wear- 
and-tear,  especially  at  the  beginning  of  training. 

In  developing  skill  (delicacy  and  accuracy  of  adjustment),  a  group  of 
muscles  develops  not  only  itself  and  its  immediate  blood-  and  nerve- 
supply,  but  without  a  doubt  no  small  part  of  the  nervous  system  also. 
A  man  who  is  very  skilful  in  one  set  of  muscular  movements  has  acquired 
much  more  than  adroitness  with  that  one  muscular  mechanism,  for  he 
has  learned  how  to  become  generally  skilled,  and  his  neuro-muscular 
mechanism  has  developed  to  a  higher  degree  of  efficiency  in  every  sort 
of  activity. 

In  just  what  this  sort  of  development  consists  so  far  as  the  muscle  is 
concerned  is  not  yet  known,  nor  indeed  are  certain  data  at  hand  as  to 
what  then  happens  in  the  nervous  system.  Keeping  in  mind  the  nature 
of  the  nervous  system,  especially  its  fibrillar  structure,  we  may  suppose 
that  in  the  muscles  there  is  a  proliferation  of  aft'erent  and  efferent  end- 
organs,  and  that  in  the  cortex  cerebri  (on  both  sides  of  Rolando's  fissure 
or  in  the  cerebellum)  a  corresponding  increased  interlacement  between 
neurones  develops.  This  sort  of  d'ft'erence  between  muscles  capable 
of  fine  adjustment  antl  those  incapable  of  it  is  apparent  in  the  number 


390  MUSCULAR  ACTION 

of  muscle-fibers  to  one  nerve-fiber  in  the  eye-muscles  compared  with  their 
number  in  the  gluteus  maximus  or  other  strong,  gross  muscle;  it  is  many 
times  greater  in  the  former  case.  In  other  words,  each  muscle-cell  is 
controlled  in  more  detail  in  a  skilled  muscle  than  one  which  is  unskilled. 
The  power  of  coordination  with  its  neighbors  is  by  this  means  greatly 
enhanced,  and  the  resulting  bodily  movements  are  within  limits  of 
accuracy  not  before  realized. 

When  this  skill  in  adjusting  movements  has  been  acquired  by  many 
functional  groups  of  muscles  in  different  parts  of  the  body,  the  nervous 
system  developing  in  ever-increasing  ratio,  we  call  the  individual  clever, 
meaning  thereby  that  he  can  do  many  things  well. 

A  person  becomes  clever  as  an  individual,  as  a  "mind,"  usually  only 
through  having  done  many  sorts  of  things  with  his  neuro-muscular 
mechanism.  This  is  a  firm  basis  for  the  philosophy  of  utilitarianism, 
and  a  reason  for  a  large  increase  in  the  "manual"  training  and  the 
"physical"  education  of  men  and  women.  Except  to  the  narrowest 
individualism,  knowing  (however  clear  and  deep  the  insight)  without 
some  sort  of  doing  is  almost  a  reproach. 

In  the  actual  psychophysical  personality,  then,  we  cannot  separate 
that  which  is  the  immediate  outcome  of  muscular  activity  from  that 
known  to  the  older  psychology  as  "mental."  These  two  aspects  develop 
together,  stand  in  the  same  grade  of  values,  and  both  take  important 
part  in  men  and  women  as  we  would  always  wish  to  know  them.  Per- 
haps at  a  later  day  physiologists  will  be  able  to  explain  this  fact,  which 
is  more  and  more  obvious  to  educators,  by  reference  to  association- 
impulses  running  ever}nvhere  in  the  body,  especially  in  the  brain. 

Special  Muscular  Functions. — The  means,  largely  muscular  and 
neural,  by  which  posture,  locomotion,  speech,  and  emotional  reactions  are 
accomplished  seem  important  enough  to  receive  special  description, 
however  Vjrief  it  must  necessarily  be  in  comparison  with  the  complexity 
of  these  processes  themselves.  Speech  especially  is  an  intricate  sub- 
ject of  importance  which  can  receive  here  by  no  means  adequate  dis- 
cussion, having  to  make  room  for  things  more  immediately  practical. 
These  brief  descriptions  will  serve  not  only  to  explain  these  particular 
neuro-muscular  processes,  but  also  as  examples  of  the  numberless 
highly  elaV)orate  coordinated  movements,  etc.,  which  the  vegetative  and 
voluntary  muscles  and  the  nervous  system  achieve. 

Posture. — ^We  have  several  times  mentioned  nuiscular  tone,  and  it  is 
in  discussing  posture  that  we  see  one  of  its  functions  so  far  as  the  skeletal 
muscles  are  concerned.  These  latter  are  not  wholly  organs  for  producing 
active  movement,  l)ut  have  another  important  use  in  maintaining  the 
body  and  its  parts  in  the  ninnl)erless  positions  into  which  previously 
they  have  placed  the  body.  During  life  this  muscular  tonus  plays  a 
very  important  part  in  our  control  of  our  organisms.  It  is  characteristic 
of  life  and  is  maintained  even  in  the  deepest  sleep.  It  departs,  however, 
at  death  unless  the  conditions  are  such  that  it  is  promptly  merged  into 
rigor  mortis.     If  one  compare  the  posture  of  a  sleeping  body  lying  flat 


MUSCULAR  ACTION  391 

on  its  back  with  a  dead  body  in  the  same  position,  the  absence  of  the 
tonus  in  the  latter  case  is  obvious  enough,  and  in  other  bodily  positions  is 
still  more  striking.  It  is  in  part  then  by  the  tonus  of  the  muscles  that 
posture  is  maintained. 

The  central  nervous  system  is  probably  the  organ  in  which  the  co- 
ordination of  muscle-tonus  is  brought  about.  How  the  body's  intention 
to  maintain  a  certain  posture  is  connected  with  the  nerves  we  have  no 
hint,  and  here  we  do  not  need  to  inquire.  With  little  doubt  the  co- 
ordinated tonus  is  maintained  in  most  postures  by  the  streaming  of  very 
numerous  mild  impulses  from  the  muscles'  nerve-centers  into  the  muscle- 
bundles.  These  do  not  occasion  a  full  twitch  of  the  muscles,  but  only 
just  enough  contraction  to  maintain,  so  to  say,  the  "status  quo."  These 
impulses  are  of  somewhat  the  same  nature  as  those  which  increase 
muscular  metabolism  without  causing  any  contraction,  spoken  of  in  our 
discussion  of  thermotaxis.  They  are  douVjtless,  however,  of  greater 
intensity  than  the  latter,  just  as  these  in  turn  are  of  less  intensity  than  the 
influences  which  bring  about  active  molar  contraction. 

It  is  interesting  to  observe  how  widely  the  intensity  of  contraction,  if 
not  of  its  stimidi,  must  vary  to  maintain  a  posture  under  the  many  vary- 
ing conditions  of  resistance  and  muscular  vigor.  Either  of  these  mechan- 
ical conditions  in  any  case  may  vary  within  wide  limits,  but  the  nervous 
system  must  and  normally  does  see  to  it  that  just  the  right  degree  of 
contraction  is  maintained  to  preserve  the  bodily  position  assumed. 

In  some  cases  the  maintenance  of  posture  does  not  rest  largely  with 
the  muscles,  for  the  bones  bear  the  weight.  By  this  means  considerable 
needless  work  is  taken  from  the  actively  metabolic  muscles  and  assumed 
by  the  tissues  (largely  bones,  tendons,  aponeuroses,  cartilages),  that  serve 
more  or  less  in  a  passive  way.  It  is  the  work  of  the  muscles  in  these  cases 
to  pose  the  various  parts  of  the  body  so  that  they  are  in  equilibrium,  and 
to  keep  them  thus,  while  the  strain  comes  largely  on  the  bones.  In  this 
way  only  a  minimum  of  exertion  is  demanded  of  the  muscles.  Perhaps 
the  most  important  illustration  of  this  is  in  standing. 

Standing. — It  was  formerly  thought  that  the  muscles  were  largely 
responsible  directly  for  the  maintenance  of  the  erect  position.  The 
work  of  Braime  and  Fischer,  v.  ]Meyer,  and  others  shows  that  the  body's 
equilibrium  is  almost  wholly  a  passive  affair  so  long  as  the  joint<'enters 
are  kept  in  the  "normal  position"  and  the  muscle-tonus  maintained. 
In  this  exact  posture  the  center  of  gravity  of  the  body  and  all  the  joint- 
centers  are  in  line.  The  knee-joints,  hip-joints,  the  atlo-axoid,  and  the 
ankle-joints  lie  in  the  same  vertical  plane  in  which  are  also  the  centers  of 
gravity  of  the  head,  trunk,  thighs,  legs,  upper  arms,  forearms,  and  hands. 
Hence  in  normal  standing  each  of  these  parts  and  joints  is  in  balance 
and  also  the  whole  body  together.  Braune  and  Fischer  found  that  the 
knee-joint's  mid-point  was  4  cm.,  the  hip-joint's  5  cm.,  and  the  atlo- 
axoid's  3.5  cm.  in  front  of  the  vertical  plane  passing  through  the  ankle- 
joint's  mid-points,  while  the  center  of  gravity  of  the  head  was  4  cm.  and 
of  the  whole  body  4.2  cm.  in  front  of  this  plane.     The  center  of  gravity 


392  MUSCULAR  ACTIOX 

of  the  trunk  is  only  0.6  cm.  behind  it.  Altogether  the  balance  is  a  very 
perfect  one  and  is  maintained  with  a  very  small  expenditure  of  effort  in 
comparison  with  the  considerable  weight  sustained. 

Ix  SITTING  the  weight  is  sustained  on  the  tuberosities  of  the  ischia,  and 
the  trunk,  leaned  either  against  some  surface  (as  the  back  of  a  chair)  or 
else  leaned  forward,  is  sustained  in  balance  somewhat  as  in  standing. 

Locomotion  consists  of  some  sort  of  rhythmic  alternation  of  the  limbs 
made  in  such  a  way  that  the  body  advances  as  a  whole.  Aside  from 
jumping  and  rolling,  the  chief  means  of  natural  human  locomotion  are 
walking,  running,  creeping,  and  swimming.  Of  these  we  need  discuss 
only  the  first  two. 

Walking  and  Running. — Braune  and  Fischer  have  advanced  some- 
what upon  the  classic  studies  of  Weber  brothers  and  of  Marey  into  the 
phenomena  of  walking  and  running.  By  attaching  tiny  electric  lamps 
to  different  parts  of  the  body,  accurately  photographing  in  the  dark  the 
respective  courses  of  these  lights,  and  afterward  working  them  out  with 
mathematical  exactness,  these  researchers  have  arrived  at  many  of  the 
actual  physical  conditions  of  these  important  motor  functions,  and  with 
surprising  precision.  For  a  general  understanding,  however,  of  these 
processes  the  instantaneous  photographs  of  Marey  (made  in  part  in 
daylight  from  a  man  running  and  in  part  in  the  dark  from  illuminated 
lines  and  lights  attached  to  the  man's  costume)  furnish  us  the  best 
material. 

The  muscles  of  walking  and  the  process  itself  are  somewhat  as  follows 
(Richer):  Pushed  forward  by  a  muscular  action,  which  will  be  noted 
later  on,  the  leg  which  is  swinging  falls  again  by  its  own  weight  on  the 
ground.  At  this  instant  it  is  in  a  condition  of  almost  complete  muscular 
relaxation  or  rest.  As  soon  as  it  begins  to  support  the  body's  weight 
again,  even  before  the  foot  is  completely  on  the  groimd,  the  muscular 
contraction  begins.  The  middle  gluteus  begins  to  shorten  and  its 
energetic  contraction  lasts  during  the  time  of  one-sided  support  to  pre- 
vent the  rotation  of  the  pelvis  by  the  swinging  leg  attached  to  it.  The 
midflle  gluteus  and  probably  also  the  gluteus  minimus  directly  oppose 
the  lateral  fall  of  the  pelvis,  and  are  aided  by  the  upper  part  of  the  gluteus 
maximus  and  the  tensor  fasciae  latse.  The  gluteus  maximus  in  its 
entirety,  meanwhile,  contracts  during  the  entire  posterior  step  and  thus 
prevents  the  falling  of  the  trunk  forward,  but  its  activity  stops  at  the 
moment  of  verticality  and  does  not  begin  again  during  the  anterior  step. 
The  quadriceps  also  is  one  of  the  first  muscles  of  the  supporting  leg 
to  contract,  and  maintains  thus  the  extension  of  the  weight-bearing  leg 
whifh  else  would  bend;  like  the  gluteus  maximus,  it  is  quite  inactive 
during  the  anterior  step.  The  muscles  of  the  (lower)  leg  are  all  slightly 
relaxed  during  the  posterior  step,  l:)ut  at  the  time  of  verticality  the  poste- 
rior and  lateral  muscles  contract  vigorously,  the  contraction  increasing  to 
the  step's  end.  The  calf-muscles  (gastrocnemii  and  peronei)  energetic- 
allv  raise  the  heel,  and  the  latter,  as  it  leaves  the  ground,  raises  and 
pushes  forward  the  body  simultaneously.     Hence  these  muscles  are  the 


MUSCULAR  ACTION 


393 


true  agents  of  propulsion.  Flattening  of  the  arch  of  the  foot  is  prevented 
only  by  the  powerful  action  of  the  lateral  })eronei.  The  posterior 
femoral  muscles,  flexors  of  the  supporting  leg,  begin  contracting  during 
the  anterior  step,  and  the  contraction  soon  becomes  marked  and  flexes 
tlie  leg  oft"  the  ground. 

The  previously  supporting  leg  now  becomes  the  swinging  leg.  At 
this  moment  the  gastrocnemii  and  the  peronei  relax,  and  at  the  same 
time  the  extensors  of  the  toes  and  the  tibialis  anticus  contract,  the  last 
serving  to  raise  the  toes  off  the  ground  to  prevent  their  touching  it  as  the 
leg  swings.  The  flexors  of  the  leg  are  contracted,  but  the  flexors  of 
the  thigh  on  the  pelvis  (sartorius,  etc.)  contract  so  as  to  draw  forward 
the  thigh  and  the  rest  of  the  leg.  Thus  the  swinging  leg  advances,  but  as 
it  passes  the  vertical  the  quadriceps  femoris  shortens  v  gorously  so  as  to 
extend  the  leg  from  the  thigh;  this  is  a  quick  movement  and  is  quite 
finished  before  the  advancing  leg  has  stopped.  (The  swelling  seen  in 
the  thigh  later  than  this  is  due  to  the  relaxation  rather  than  to  the  con- 
traction of  this  large  mass  of  muscle) 


Fig,  241 


The  periods  of  a  double-step.  The  first  shows  the  period  of  double  support,  the  second  the 
posterior  step,  the  third  the  moment  of  verticality,  the  fourth  the  anterior  step,  and  the  last  the 
period  again  of  double  support.      (Richer.) 

Other  accompanying  contractions  are  to  be  seen:  The  spinal  muscles 
contract  on  the  side  of  the  oscillating  leg,  as  does  also  the  deltoid,  the 
anterior  and  posterior  fibers  of  the  latter  controlling  the  natural  swinging 
of  the  arms. 

The  work  of  Fischer,  then,  tends  to  minimize  the  old  passive  pendular 
movement  notion  of  the  Weber  brothers  and  to  show  that  it  is  largely  a 
muscular  propulsion. 

In  running  the  phenomena  are  essentially  those  of  walking,  the  main 
difference  being  in  the  vigor  of  the  supporting  leg's  action.  All  the 
movements  are  exaggerated  and  the  supporting  leg  (gastrocnemius)  in 
extending  the  foot  on  the  ankle  raises  the  body  so  strongly  that  the  latter 
entirely  clears  the  ground  and  falls,  a  moment  later,  considerably  fur- 
ther forward  on  the  far-extending  other  leg.  Running,  like  walking,  is 
then  a  system  of  fallings  first  on  one  leg  and  then  on  the  other.  The 
energy  expended  is  about  double  (^larey)  that  of  riding  a  bicycle,  but 


394  MUSCULAR  ACTION 

partly  because  the  number  of  nervous  and  muscular  movements  is  much 
greater,  the  fatigue  is  much  more  than  in  this  ratio.  The  cerebral  center 
may  be  the  corpus  striatum. 

Speech. — The  neuromuscular  mechanism  by  which  we  use  our  voices 
is  one  of  the  most  complex  in  the  body.  ^Vhile  complicated  in  the  large 
number  of  nerves  of  muscles  and  muscle-bundles  employed,  it  is  doubt- 
less vastly  more  so  as  respects  its  central  neural  apparatus.  This  has  to 
put  it  in  intimate  relation  on  the  one  hand  with  practically  all  aspects  of 
our  intelligence,  and  on  the  other  with  the  centers  of  many  of  the  motor 
functions.  It  is  only  artificially,  then,  that  we  can  separate  the  phenom- 
ena of  speaking  from  the  more  mental  principles  of  language;  they  are 
aspects  of  one  and  the  same  broad  function,  the  expression  of  intelligence. 
"Without  this  we  would  still  be  brutes.  In  writing,  the  same  language- 
phenomena  are  employed,  but  the  voice-muscles,  etc.,  partake  in  it  only 
reflexly  and  sympathetically.  Here  we  are  concerned,  then,  only  with 
voice-production  and  not  at  all  with  language  itself  or  with  the  other 
modes  of  its  expression.  The  physiology  of  language,  merging  into  the 
formation  of  spoken  and  written  words  on  one  side  and  the  abstruse 
psychology  of  conception  on  the  other,  is  outside  our  present  range 
(see  page  417). 

The  apparatus  concerned  in  vocalization  includes  the  muscles  and 
nerves  of  most  of  the  external  respiratory  mechanism;  the  larynx;  the 
air-chambers  connected  with  the  nose;  and  the  mouth-cavity,  including 
the  tongue  and  lips.  These  all  are  active  instruments  of  speech.  For 
the  detailed  anatomy  of  these  parts  the  reader  is  earnestly  referred  to 
anatomical  text-books  in  order  that  he  may  clearly  understand  the  rela- 
tions of  these  organs  to  each  other.  The  most  complex  part  of  this 
mechanism,  aside  from  the  nerves  connected  with  it,  is  the  larynx; 
its  parts  and  their  respective  functions  are  even  yet,  after  three  centuries 
of  study,  only  partly  determined.  The  thorax  furnishes  most  of  the 
motive  power  of  vocalization.  The  larynx  contains  the  vibrating  sound- 
producers  proper.  The  nasal  air-chambers  are  the  chief  resonators  of 
this  sound-producer.  The  mouth-cavity  and  the  lips,  tongue,  and  teeth 
within  it  or  part  of  its  walls  are  largely  the  means  by  which  the  "sound" 
sent  into  it  from  the  larynx  are  differentiated  into  words  and  other 
utterances  with  a  myriad  shades  of  tones  and  meaning.  Controlling 
all  of  these  and  coordinating  them  into  one  useful  mechanism,  the  valued 
servant  of  the  individual,  are  the  nerves  and  the  nerve-centers  connected 
with  them. 

The  respiratory  beij.ows  is  concernefl  with  voice  chiefly  in  the 
expiratory  phase  of  its  mf)vements.  In  very  high-pitclied  singing  or 
speaking  the  current  sent  through  the  trachea  is  a  powerful  one,  one 
estimate  making  the  tracheal  air-pressure  70  mm.  of  mercury  or  more. 
In  ordinary  tones  it  is  probably  not  over  one-sixth  of  this  amount.  It  is 
to  furnish  this  draft  of  the  tidal  air  that  the  thorax  is  used  in  speaking. 
In  this  function  of  the  bellows-mechanism  of  the  trunk  one  sees  how 
perfectly  under  voluntary  guidance  the  respiratory  muscles  are.     With- 


MUSCULAR  ACTION  395 

out  this  minute  and  careful  control  of  the  air-currents  through  the  larynx 
the  significant  functions  of  cultured  and  emotional  speaking  and  singing 
would  be  quite  impossible.  When  one  considers  that  the  abdominal 
muscles,  the  diaphragm,  and  many  muscles  of  the  thorax  take  part  in 
the  respiratory  movements,  the  wide-reaching  extent  in  the  body  of  the 
influence  of  vocalization  is  obvious. 

The  larynx  is  the  automatically  adjusting  reed-box  by  which  the 
voice  is  actually  produced  except  apparently  in  one  sort  of  whispering. 
The  essential  organs  of  the  larynx  are  the  true  vocal  cords.  The  tonal 
conditions  of  these  vibrating  reeds  are  determined  and  varied  by  the 
nine  intrinsic  muscles  of  the  larynx,  not  including  those  attached  to  the 
epiglottis.  In  general  terms  there  are  four  duties  which  these  muscles 
perform:  to  increase  and  decrease  the  ejffective  vibratory  length  of  the 
vocal  cords  and  the  space  between  them.  The  former  pair  of  functions 
concern  the  pitch  of  the  sound,  the  latter  its  loudness. 

The  air-chambers  connected  with  the  throat,  nose,  and  mouth, 
including  the  antrum  of  Highmore,  are  resonators  of  the  tones  started 
in  the  larynx.  Without  these  chambers  the  sounds  produced  by  the 
vocal  cords  would  have  little  of  that  volume  and  richness  in  some  degree 
characteristic  of  all  voices.  It  is  largely  owing  to  the  uniqueness  of  the 
combined  shape  of  these  chambers  in  each  individual  that  each  voice  is 
different  from  every  other. 

The  mouth-cavity,  including  the  tongue  and  the  lips,  is,  like  the  other 
chambers  above  and  in  connection  with  the  larynx,  when  closed  a 
resonance-chamber  of  the  fundamentals  and  partials  of  the  voice.  It  is, 
however,  much  more  than  merely  this,  for  only  by  means  of  its  muscular 
walls,  so  cleverly  trained  in  the  passing  centuries,  has  spoken  language 
become  possible.  Speech  is  primarily  a  large  ri\<\  elaborate  system  of 
vocal  symbols,  and  these  are  produced  almost  wholly  through  the  proper 
adjustment  and  coordination  of  the  muscles  in  and  about  the  mouth- 
cavity.  Of  these  muscles,  the  tongue  is  by  far  the  most  versatile, 
although  the  soft  palate  and  the  lips  also  play  important  parts  in  enun- 
ciation. 

The  nervous  control  of  the  mechanism  of  voice-production  re- 
quires little  special  mention,  for  the  nerves  actuating  the  separate  parts 
of  the  mechanism  have  been  already  discussed,  while  about  the  central 
connections  producing  the  complicated  coordinations  nothing  in  detail 
is  known.  To  the  student  of  mental  processes  especially  this  neural 
apparatus  would  have  great  importance  could  he  know  it,  since  it  serves 
better  than  any  other  in  the  body  perhaps  to  link  the  events  of  idea- 
formation  with  the  motor  events  expressing  them — it  "connects"  more 
closely  than  elsewhere,  it  may  be,  the  body  and  the  intellectual  aspects 
of  the  mind.  We  must  think  that  the  mental  aspect  of  an  idea  is 
somehow  intimately  associated  with  its  symbols  of-  motor  expression  to 
others,  but  we  do  not  know  just  where  or  even  in  what  manner  to  look 
to  discover  its  material  mechanism.  Vocal  movements,  like  other 
gestures,  involve  muscles  and  the  nerves  which  coordinate  them,  but  the 


396  MUSCULAR  ACTION 

relations  of  the  speech-center  with  other  aspects  of  body  and  of  mind 
we  can  as  yet  but  guess  about.  Here  in  especial  degree  hypotheses 
are  vain,  so  far  apart  in  character  are  an  idea  and  the  moving  parts 
which  express  it. 

The  chief  nerve-trunks  containing  fibers  concerned  in  speech  and 
respiration  have  already  been  mentioned.  The  larynx  is  supplied  by 
the  superior  laryngeal  and  by  the  inferior  or  recurrent  laryngeal  branches 
of  the  vagus.  The  other  nerves  vitally  concerned  in  speech  are  prac- 
tically those  of  deglutition  and  of  mastication. 

The  speech-center  in  the  child,  according  to  Gowers,  like  most  centers, 
is  probably  bilateral,  but  it  gradually  builds  most  of  its  connections  into 
the  left  hemisphere.  ^^Tiether  or  not  the  common  and  unfortunate 
development  of  one-sided  hand-function,  "right-handedness,"  is  the 
cause  of  this  unilateral  location  of  the  speech-center  is  as  yet  not  known. 
]More  likely  than  not,  however,  this  is  the  reason  of  it.  In  left-handed 
persons  the  center  is  in  the  right  hemisphere.  There  is  considerable 
evidence  that  in  childhood  or  later  if  one  speech-center  area  be  destroyed 
the  same  region  of  the  opposite  hemisphere  may  take  up  its  function  of 
remembering  the  motor  ideas,  etc.,  of  speech.  We  have  seen  above 
that  the  real  motor-center  of  the  vocal  process  is  in  the  ambiguous 
nucleus  of  the  vagus,  the  influence  coming  to  it  (by  way  of  the  spinal 
accessory?)  from  some  part  of  the  cortex  cerebri  above  by  some  road  as 
yet  not  sure.  By  its  association-powers  this  knot  of  fibers  wherever  it  be 
placed  in  the  cortex,  over-sees  or  perhaps  controls  the  more  mechanical 
and  truly  motor  centers  in  the  cerebellum,  medulla,  or  cord,  it  contains 
the  kinesthetic  traces  used  in  articulating  words. 

The  exact  location  of  this  supervising  associating  center  in  the  cortex 
was  determined  by  Broca  following  up  valuable  w^ork  by  Bouilland,  who 
in  turn  was  inspired  (Howell)  by  the  work  of  the  famous  pre-scientific 
phrenologist  Goll.  It  is  seated  undoubtedly  in  the  third  or  lower  frontal 
convolution  in  the  region  surrounding  the  short  anterior  vertical  branch 
of  the  fissure  of  Sylvius.  In  this  area  of  four  or  five  square  centimeters 
of  knotted  neurones  are  somehow  stored  and  associated  the  kines- 
thetic directions  for  moving  the  speech-organs  via  other  centers  in  the 
medulla.  It  is  to  be  noted  that  this  center  is  part  of  the  so-called 
"motor  area"  of  the  brain,  or  at  least  it  is  close  to  the  region  representing 
all  movements  of  the  neck,  face,  and  mouth.  Just  below  this  area,  on 
the  other  side  of  the  Sylvian  fissure  in  the  superior  gyrus  of  the  temporal 
lobe  are  traced  the  memories  of  the  word-symbols  themselves  in  their 
relations  to  the  senses  and  other  yet  more  purely  psychical  conditions. 
From  this  former  region  the  motor  fibers  extend  deeply  inward  to  the 
posterior  part  of  tlie  lenticular  nucleus  and  then  downward  to  the 
medulla  as  above  mentioned. 

Aphasia. — The  various  kinds  of  aphasia  are  practically  important 
sometimes  for  locating  cerebral  disease,  and  theoretically  of  great  interest 
because  of  the  light  they  tlirow  on  the  psychomotor  a])paratus  of  speech 
and  of  language.     They  are  varieties  of  sj)eech-(lefect  corresponding  to 


MUSCULAR  ACTION  397 

the  different  aspects  of  the  total  function  of  these  processes.  Re- 
moval by  cyst,  tumor,  or  wound  of  the  motor  speech-area  noted  aljf)ve 
causes  loss  of  speaking-power.  The  memory-directions  for  working 
the  right  muscles  in  the  right  order  then  no  longer  exist,  at  least  in  this 
cortical  region  of  voluntary  use.  This  defect  is  motor  aphasia,  ayhemia. 
In  case  the  motor  inability  is  in  using  the  hands  for  writing  instead  of 
the  throat,  etc.,  for  speaking,  it  is  agraphia.  AMien  there  is  not  a  com- 
plete loss  of  speech,  but  only  a  defect  (as  in  paresis,  intoxication,  etc.), 
it  is  called  ataxic  aphasia.  Other  kinds  of  speech-derangement,  caused 
by  mental  rather  than  by  bodily  motor  disturbance,  are  rather  misleadingly 
called  sensory  aphasias.  Thus  amnesic  aphasia  indicates  a  loss  of  mem- 
ory of  either  some  words  or  all  words.  The  forgetting  of  proper  names, 
especially  those  of  persons,  is  its  most  common  and  least  abnormal  form. 
There  is  word-blindness  and  word-deafness,  wherein  the  words  are  read 
and  heard  properly  but  not  recognized  as  symbols  of  meanings,  not 
"apperceived."  In  paraphasia  the  word-sounds  or  word-shapes  are 
recognized  but  associated  with  the  wrong  meanings,  wrongly  apperceived. 
The  opposite  condition  is  a  variety  of  ataxic  aphasia  relatively  common 
in  which  the  patient  has  the  meaning  in  his  mind  properly  but  uses  the 
wrong  words  in  trying  to  express  it.  There  are  many  combinations  of 
these  various  conditions  found  at  times,  but  for  description  of  them  works 
on  nervous  and  mental  disease  should  be  consulted.  These  aphasias  are 
all  of  much  interest  physiologically  as  examples  of  direct  psychophysical 
relations  and  of  the  vast  complexity  of  brain-processes. 

Emotional  Reactions. — As  will  be  pointed  out  more  explicitly  in  the 
next  chapter,  the  bodily  aspects  of  the  actual  individual,  as  distinct 
from  his  mental  aspects,  are  not  all  related  to  his  "will"  (voluntary), 
or  to  carrying  on  reflexly  the  vegetative,  somatic,  and  protective  func- 
tions of  the  body.  Besides  these  there  is  a  class  of  movements  and 
tendencies  to  movement  called  strains  which  form  part  of  the  emotional 
feeling-aspects  of  the  individual.  These  are  commonly  called  emotional 
reactions  or  emotional  "expressions,"  but  they  are  also  essential  parts  of 
feeling-phenomena  too  simple  and  feeble  to  be  called  true  emotions. 
Thus,  when  we  feel  surprised  our  muscles  make  at  least  our  faces 
show  it,  unless  (as  is  likely)  we  have  trained  ourselves  to  inhibit  these 
muscular  movements.  If  we  feel  very  glad  of  something  and  are 
alone,  that  is,  have  no  reason  for  inhibiting  the  natural  movements  and 
"repressing  our  feelings,"  we  are  apt  to  smile  and  laugh  and  perhaps 
be  more  lively  and  expansive  than  usual.  When  we  are  suffering  from 
an  acute  sorrow  the  opposite  tendencies  are  obvious  in  our  "manner," 
that  is,  in  our  muscular  conduct.  In  terror  our  face-muscles  move  in  a 
certain  combination  and  make  us  "look  frightened,"  and  if  we  are 
angered  the  infant  even  recognizes  it  instinctively  because  of  the  par- 
ticular set  of  muscle-movements  characteristic  of  the  emotion  of  anger. 
The  classic  works  of  Darwin,  Piderit,  Lavater,  Rudolph,  etc.,  describe 
and  finely  picture  this  wealth  of  emotional  reaction  in  man  and  other 
animals.     The  striking  thing  about  the  matter  physiologically  is  that 


398  MUSCULAR  ACTION 

every  feeling  and  emotion  has  a  different  set  of  movements  involving, 
when  strong  enough,  practically  the  whole  body.  In  these  complex  sets 
of  movements  the  muscles  of  course  play  the  chief  part,  whether  in  the 
wall  of  an  arteriole  or  of  the  gut,  in  the  diaphragm,  or  in  the  face.  Epi- 
thelium also  takes  part.  Our  present  inquiry  asks  how  these  motor  reac- 
tions are  coordinated  and  the  principles,  if  there  are  any,  underlying 
the  different  sets  of  movements.  The  more  psychic  aspects  of  feeling 
are  discussed  in  the  next  chapter,  so  here  we  briefly  glance  only  at  the 
"reactions"  in  so  far  as  they  are  a  muscular  function. 

We  have  seen  that  the  motor  nervous  apparatus  works  probably  on 
the  reciprocating  plan:  when  one  muscle-group  is  caused  to  contract 
its  antagonist  is  correspondingly  inhibited  and  relaxed.  About  the 
hinge-joints  are  two  opposed  sets  of  muscles,  the  one  flexor  and  the  other 
extensor  in  function.  There  are  pronators  and  supinators,  elevators 
and  depressors,  adductors  and  abductors,  sphincters  or  constrictors  and 
dilators,  the  members  of  each  pair  being  opposed  or  opposite  in  action 
to  each  other.  Again,  there  is  another  sort  of  antagonism  of  a  vascular 
sort  in  the  vaso-motor  mechanism.  WTien  vaso-constriction  occurs  in  a 
more  or  less  well-defined  area  of  the  body  vaso-dilatation  is  brought  about 
to  compensate  in  some  other  area.  Finally  w^e  find,  if  we  compare  vari- 
ous emotions,  that  there  is  antagonism  in  the  degree  of  muscle-activity: 
in  grief,  for  example,  we  tend  to  use  our  muscles  little,  in  joy  and  glad- 
ness and  pleasure  much.     . 

These  basal  antagonisms  in  the  action  of  the  muscles  have  been  studied 
not  a  little  in  relation  to  emotions  which  involve  them  in  some  char- 
acteristic ways.  ]\Iixed  up  with  the  theories  of  pleasure  and  of  pain,  for 
example,  is  the  degree  of  general  activity:  pain  hinders  metabolism 
and  activity,  and  pleasure  furthers  it.  In  general,  however,  the  only 
correspondence  which  can  be  made  out  between  aspects  of  feeling  and 
emotion  and  these  motor  oppositions  (besides  that  just  mentioned)  is 
a  general  agreement  between  pleasant  emotions  and  contraction  of 
extensor  muscles  and  unpleasant  emotions  and  the  action  of  muscles 
classed  as  flexors.  To  this  rule  even  there  are  many  exceptions,  just  as 
some  beneficial  things  have  a  bitter  taste  and  many  deadly  poisons  are 
sweet.  Some  emotions  lack  more  or  less  any  tone  of  the  pleasant  or 
unpleasant,  yet  have  well-marked  muscular  reactions.  It  is  possible 
that  some  quality  of  the  mental  side  of  an  emotion  other  than  pleasant- 
ness or  unpleasantness  determines  the  motor  combination.  It  is  even 
possible  that  we  may  have  finally  to  look  to  the  intricacies  of  the  nervous 
"net"  and  to  its  connections  with  the  elements  of  the  muscle-fabric 
in  order  to  account  for  the  motor  aspects  of  emotions.  Meanwhile  there 
is  always  before  us  for  admiration  this  marvellous  structure  of  muscle 
and  nerve  and  fjtiicr  tissuess  wliose  parts  and  action-principles  even 
centuries  of  self-rewanHng  but  tantalizing  research  may  not  exhaust. 


CHAPTER    XII. 

MENTAL   FU.XCTIOX. 

Another  of  the  various  modes  of  activity  which  are  in  one  way  or 
another  directly  connected  with  the  human  organism  is  consciousness,  or 
mind.  Reduced  to  its  very  simplest  biological  terms,  this  is  the  feeling  of 
being  alive.  It  is  necessary  to  discuss  this  aspect  of  the  individual  for 
several  reasons,  the  most  important  of  which  perhaps  is  the  fact,  obvious 
but  often  ignored,  that  every  person  is  not  merely  a  body  but  also  a  mind, 
neither  being  complete  or  easily  thinkable  without  the  other.  It  is  one  of 
the  greatest  defects  in  the  practice  of  the  scientific  medical  art  that  many 
far  too  often  disregard  the  mental  aspect  of  the  individual.  Indeed, 
only  in  very  recent  years  has  the  medical  profession  as  a  whole  begun  to 
realize  the  importance  of  this  mental  "half"  of  his  patients.  These  two 
aspects  practically  inter-act  in  almost  every  phase,  and  the  mind  is 
scarcely  more  dependent  on  the  body  than  is  the  body  on  the  mind.  In 
no  sense,  however,  is  the  mental  process  a  function  of  the  body  but  rather 
in  reality  the  body  is  only  the  material  instrument  of  the  mind.  We  have 
no  intention  of  entering  for  a  moment  upon  any  metaphysical  discussion 
of  the  relations  of  body  and  mind.  It  is  only  necessary  here  to  assume 
the  common  theory  that  these  "two"  probably  are  different  aspects  of 
one  reality.  If  we  take  Fechner's  famous  simile  of  the  arc  of  a  circle, 
the  bodily  events  are  like  the  outer  aspect  of  this  curve  and  the  mental 
process  the  same  line  as  seen  from  the  inside.  Consciousness,  properly 
speaking,  cannot  be  defined.  Its  only  definition  consists  in  living  it, 
and  yet  we  may  say  that  in  a  narrow  sense  the  mental  process  is  the 
experience  that  an  animal  has  of  its  external  and  internal  environment. 

Consciousness  is  inherently  a  process,  and  psychology  no  longer  pur- 
sues its  ancient  search  after  a  substantial  soul.  The  soul  for  modern 
thought  is  an  ethical  thing  and  psychologically  that  which  James  has 
made  known  the  world  over  as  the  stream  of  consciousness.  In  the 
following  brief  description  of  the  mental  functions  all  that  we  wish  to 
examine  is  facts,  the  "what"  without  the  "how"  and  usually  without 
the  "why."  We  desire  only  a  simple,  straight-forward  description  of 
the  outlines  of  the  human  mental  process  in  those  aspects  most  closely 
connected  with  the  organism.  This  is  properly  a  part  of  physiology, 
not  only  because  from  any  and  every  point  of  view  mind  is  connected 
undeniably  with  organic  function,  but  because  the  physician  and  the 
student  need  to  know  much  better  than  they  often  do  the  other  side  of 
man's  nature,  about  his  "fire"  as  well  as  about  the  structure  of  his 
"clay."     The   time  has  nearly  come  when   the  scientific   physiologist 


400  MEXTAL  FUXCTION 

will  no  longer  shy  at  hearing  the  word  consciousness  or  even  at  the  sight 
of  the  psychologist  in  his  laboratory,  for  the  truth  is  marching  on  that 
the  subject-matter  and  the  methods  of  science  do  not,  after  all,  conflict 
with  or  even  necessarily  concern  the  honored  interests  of  philosophy. 
In  merely  describing  in  a  simple  way  the  phenomena  of  mind,  we  need 
never  go  outside  of  science,  nor  indeed  outside  of  physiology  considered 
as  the  general  science  of  vital  processes. 

There  is  nothing  in  consciousness  more  difficult  of  understanding 
than  many  of  the  functions  and  structures  already  described,  of  the 
kidney,  the  brain,  or  the  lung.  The  impression  to  the  contrary,  so 
common  among  medical  students,  arises  partly  from  the  novelty  of  the 
mental  topics  but  more  from  the  fact  that  these  psychic  objects  cannot 
be  literally  handled  but  must  be  felt  otherwise  and  studied  as  they  stand 
before  the  mind  in  the  imagination.  Bones  may  be  taken  out  of  the  box 
and  their  tuberosities  compared  visually  with  the  pictures  in  the  text- 
book, and  brains  and  muscles  may  be  handled  in  the  dissecting-room, 
cut  open,  and  preserved.  We  are  accustomed  to  this  mode  of  studying 
material  things,  and  it  is  easy  for  us.  Here,  on  the  other  hand,  are  only 
sensations,  emotions,  percepts,  ideas,  objects  not  material  but  objects 
none  the  less,  well-defined,  separate  in  a  way,  with  qualities,  relations, 
and  real.  Indeed  the  aspects  of  consciousness  are  the  realest  of  all 
real  things,  ^^^lo  is  there  whose  life  has  not  been  influenced  more  by 
some  ideas  or  volitions  or  feelings  than  by  every  sort  of  material  object 
whatsoever?  For  every  man  crushed  by  a  falling  rock  or  an  overturning 
car  dozens  are  crushed  by  mental  objects  such  as  these  others.  These 
things,  then,  are  significant  and  real  and  can  be  taken  apart  somewhat, 
observed  and  examined,  analyzed,  synthesized,  classified  in  many  ways 
— in  short,  scientifically  studied. 

Terms  different  from  those  of  anatomy  of  course  will  have  to  be 
employed  at  times  and  psychological  expressions  with  technical  meanings. 
In  no  other  way  can  things  be  scientifically,  that  is  tersely  and  accurately, 
denoted  or  described.  The  terms,  however,  are  mostly  simple  compared 
with  many  in  the  text-books  of  anatomy,  histology,  and  chemistry  to 
which  we  are  accustomed.  It  is  their  novelty  alone  which  makes  them 
now  and  then  somewhat  forbidding. 

The  "Functions"  of  the  Mental  Process. — In  reality  the  mental  process 
as  experienced  by  individuals  has  no  function;  it  is  the  essential  part  of 
the  personality.  Properly  speaking,  then,  it  is  only  the  body  which  has 
functions:  that  it  may  serve  as  the  temporary  instrument  of  the  per- 
sonality. Xone  the  less,  from  a  purely  biological  point  of  view  we  may 
point  out  one  or  two  uses  or  functions  of  this  "internal  radiance,"  as 
Morat  rather  strikingly  calls  consciousness.  The  most  conspicuous  of 
these  })y  far  are  those  which  inhere  in  memory  and  in  the  synthetic 
activities  of  mind.  It  is  eas^'  to  think  of  an  unconscious  organic  machine 
which  woukl  receive  and  preserve  impressions  (such  as  those  which 
produce  light  and  sound)  from  the  environment,  l)ut  it  is  perhaps  im- 
possible to  imagine  any  means,  other  than  that  we  call  consciousness,  by 


MENTAL  FUNCTION  401 

which  all  these  experiences  could  be  summarized,  systematized,  and 
recalled  at  any  future  time  for  the  benefit  of  the  organism.  Minot's 
formula  for  this  fact  is  that  consciousness  dischronates  the  products  of 
experience.  It  does  more  than  this,  however,  for  it  combines  them, 
allows  or  causes  them  to  interact  and  so  produce  results  often  entirely 
new  and  of  the  utmost  use  in  the  evolution  of  humanity. 

Without  consciousness  human  life  were  well-nigh  inconceivable.  It 
could  have  no  interest  either  to  God  or  to  man,  would  be  nothing  more 
than  a  self-repairing  and  self-reproducing  material  process,  part  of  the 
inert  universe  of  matter  which  is  dead  and  meaningless.  There  would 
be  no  persisting  unity  in  this  automatic  mechanism — without  conscious- 
ness in  its  sensory  aspects  our  very  feet  would  be  foreign  bodies  to  us. 
In  fact,  we  could  not  speak  of  "our"  or  "us"  at  all,  for  there  would  be  no 
unitv,  or  if  a  material  unitv  could  be  maintained,  there  would  be  nothing 
to  lend  it  value,  no  self-consciousness,  no  significant  human  life.  It  is 
only  from  such  points  of  view  as  these  that  we  can  mention  certain 
"functions"  of  consciousness. 

Certain  General  Characteristics  of  the  Mental  Process. — When  we  closely 
observe  for  a  time  the  stream  of  consciousness  as  it  passes  in  our  expe- 
rience we  find  at  least  three  conspicuous  characteristics  which  are 
universal  (James). 

We  shall  be  most  strongly  impressed  perhaps  with  the  continual 
changefulness  of  the  content  of  this  passing  "stream."  Indeed,  if  we 
examine  closely  or  think  over  the  nature  of  that  which  "passes  through 
our  minds"  for  say  one  minute,  we  are  apt  to  be  struck  with  the  fact 
that  although  similar  experiences  may  recur  meanwhile,  the  same 
thought  for  example,  twice,  these  are  never  twice  exactly  alike.  There 
is  perpetual  change  here  as  elsewhere  in  Nature  and  especially  in  organic 
life.  We  never  actually  experience  anything  more  than  this  process, 
this  ever-changing  yet  persistent  conscious  tide,  now  narrow  and  swift, 
now  broader  and  gentle  and  slow.  This  changefulness  seems  to  be 
dependent  all  the  while  on  the  changing  bodily  life — although  perhaps 
we  never  can  discover  exactly  how.  If  the  mental  process  has  one  con- 
stant characteristic  it  is  this  of  constant  change,  and  "nought  is  constant 
in  the  world  but  change." 

Because  the  bodily  life  is  similarly  in  "perpetual  flux,"  in  continual" 
molecular  and  molar  movement,  it  is  natural  to  say  that  the  former 
changefulness  is  in  some  way  related  to  the  latter  changefulness  just  as 
a  sensation  involves  movements  in  a  sense-organ  and  in  certain  nerves 
and  centers.  One  need  only  look  backu'ard  and  review  the  functions 
of  the  organism  to  appreciate  that  material  movement  and  activity  are 
universal  in  them.  Protoplasm  itself  is  largely  water  in  order  that  its 
essential  function,  adapted  and  varied  activity,  may  be  carried  out. 
Anabolism  and  katabolism  everywhere  go  hand  in  hand  and  both  have 
as  their  essence  none  other  than  molecular  change.  Into  all  the  sense- 
organs  is  continually  pouring  a  stream  of  stimuli,  which  are  themselves 
activity  and  which  produce  activity  in  every  portion  of  the  nervous 
26 


402  MENTAL  FUXCTIOX 

system.  Every  muscle-fiber  is  continually  in  a  state  of  at  least  tonic 
contraction,  and  every  viscus  of  the  thorax  and  the  abdomen  knows  only 
a  relative  sort  of  rest.  Thus  changeful  is  the  "physical  basis"  of  the 
mental  process,  but  how  it  is  not  here  our  business  to  inquire. 

Another  characteristic  of  the  stream  of  consciousness  is  that  while 
thus  made  up  of  "parts,"  yet  these  more  or  less  merge  into  each  other  and 
form  a  vniiy.  In  technical  terms  consciousness  is  a  continuum.  In  a 
similar  way  an  hour  is  a  continuous  series  of  minutes  and  seconds,  and  a 
river,  although  made  up  of  drops  or  gallons,  is  yet  a  continuum  of  water 
flowing  as  a  stream.  A  little  later  we  shall  see  something  of  the  nature 
or  at  least  of  the  origin  of  these  quasi  parts  which  pass  into  the  continuum 
of  consciousness.  As  long  as  life  endures  the  mental  process  stops  no 
more  than  does  the  metabolism  of  the  heart  or  the  chemical  activities 
of  the  brain,  although  its  intensity  and  its  breadth  and  depth  vary  greatly 
from  minute  to  minute,  and  become  much  lessened  especially  during 
sleep.  Heraclitus  of  old  used  to  say  that  a  man  could  bathe  in  a  river 
only  once,  for  the  river  in  which  he  bathed  the  second  time  was  no 
longer  the  same.  Closer  analysis  of  the  stream  of  consciousness  suggests 
that  a  person  cannot  bathe  in  the  same  river  even  once,  for  even  while 
he  is  bathing  the  stream  is  changing  around  him.  It  is  the  chief  purpose 
of  descriptive  psychology  to  make  plain  the  numerous  shifting  but 
recurring  qualities  of  this  conscious  river. 

The  third  characteristic  of  consciousness  of  which  the  introspecting 
individual  is  always  aware  is  that  its  states  are  invariably  referred  to  a 
unifying  fersonaliiy.  Continually  there  is  self-reference,  a  certainty 
of  a  personal  identity.  It  is  only  in  abnormal  conditions  whose  physical 
"basis"  is  unknown  that  the  mental  process  related  to  any  organism 
loses  its  identity  and  splits  into  two  or  more  personalities.  Here  is  one 
of  the  paradoxes  which  continually  remind  us  of  the  intricacy  of  things. 
Notwithstanding  this,  however,  we  may  be  sure  that  the  mental  process 
of  the  normal  man  or  woman  is  always  unified  by  an  underlying  sense 
of  individuality.  The  feelings  we  experience  and  the  thoughts  we 
think  get  their  value  for  us  only  as  they  come  directly  or  indirectly  into 
relation  with  this  personal  suVjjectivity  which  behind,  beneath,  and  all 
through  this  tide  of  changing  experience  persists  unchanged.  By  this 
alone  consciousness  is  made  real,  kept  in  range  of  flesh  and  blood,  made 
something  more  than  the  evanescent  shadow  of  a  dream. 

This  individuality  not  only  experiences  the  stream  of  consciousness,  but 
directs  it  to  a  greater  or  a  less  degree.  We  cannot  only  control  and 
force  our  thoughts  into  any  desired  direction  under  normal  conditions, 
but  our  feelings  are  more  or  less  subconsciously  determined  by  the 
nature  of  our  personalities  as  developed  by  our  experience.  AMiat  one 
.sees  and  takes  an  interest  in  is  determined  by  no  means  wholly  by  the 
nature  of  what  his  eyes  actually  see.  What  we  perceive  is  often  to  a  large 
extent  decided  by  what  is  already  present  in  our  minds.  A  lumberman, 
for  example,  sees  in  a  forest  the  size  and  straightness  and  number  and 
proportions  of  the  trees.     An  artist  sees  in  the  same  trees  only  their 


MENTAL  FUNCTION  403 

beauty.  A  trapper  sees  them  as  the  homes  of  animals  and  as  sources 
of  firewood.  The  forester  and  the  botanist  find  in  them  chiefly  a 
subject  for  study.  Yet  the  forest  of  trees  has  mostly  the  same  physical 
properties  for  all.  It  is  the  nature  of  the  perceiving  self,  as  determined 
largely  bv  its  habits  or  its  will,  that  decides  the  direction  of  the  conscious- 
ness  of  that  individual.  We  should  expect,  for  example,  a  clergyman 
who  saw  a  street-fight  to  try  to  stop  it  in  some  way,  but  if  a  passing 
pugilist  did  so  we  might  be  somewhat  surprised.  The  nature  of  the 
selfness  then  determines  not  only  the  trend  of  the  internal  consciousness 
but  the  external  bodily  activity  as  well. 

Besides  these  three  general  characteristics  of  the  mental  process,  we 
find  differences  in  quality,  quantity,  and  intensity.  The  qualities  we 
shall  soon  attempt  to  discriminate  and  briefly  to  describe.  An  example 
of  quality  is  painfulness.  The  quantity  of  the  mental  process  at  any 
time  is  what  is  technically  known  as  the  extensity  of  the  experience. 
As  an  example,  the  exposed  nerves  of  four  teeth  give  a  more  extensive 
pain  than  that  of  one  would  give.  The  intensity  of  consciousness  at  any 
one  time  means  the  degree  of  interest  which  it  has  for  the  individual. 
A  severe  ache  in  a  tooth  is  more  interesting  than  a  milder  one  would  be. 

There  is  one  other  general  attribute  of  the  total  stream  of  conscious- 
ness which  must  be  noted:  it  has  at  different  times  every  degree  of  fulness. 
The  range  in  this  respect  is  from  the  most  conscious  experience  (the 
most  intense  pain,  the  most  exquisite  pleasure,  or  the  deepest  thought) 
down  to  the  vanishing-point  of  sub-consciousness  at  the  "  lower"  levels. 
From  the  physiological  point  of  view  these  sub-conscious  mental  pro- 
cesses merge  into  protoplasmic  forces,  especially  into  nervous  impulses. 

The  Descriptive  Aspects  of  Consciousness. — Introspection  of  our 
passing  mental  experience  shows  us  that  it  has  three  dominant  aspects 
that  we  may  denote  as  feeling,  willing,  and  knowing. 

The  term  aspect  used  in  this  sense  is  theoretically  important  as  well 
as  descriptive.  The  aspects  of  consciousness  are  not  parts  of  it,  but 
rather  precisely  what  the  term  itself  with  sufficient  clearness  indicates. 
If  in  every  period  of  adult  human  consciousness  we  can  discover  elements 
of  feeling,  willing,  and  knowing,  it  is  not  that  these  are  in  any  sense 
separate  portions  of  the  conscious  stream.  At  one  time  one  of  them 
may  be  the  most  conspicuous  and  the  next  moment  perhaps  another. 
These  three  are  various  ways  of  looking  at  the  mental  process,  aspects 
abstracted  for  the  purposes  of  scientific  description  from  a  continuum 
which  is  not  objectively  separable  into  different  processes.  Every 
temporal  portion  of  consciousness  (with  exceptions  which  will  be  noted 
later)  has  all  of  these  three  aspects  of  feeling,  willing,  and  knowing. 
These  phases  are  mentally  abstracted  for  purposes  of  description  as  if 
they  were  actually  separate. 

Feeling. — The  word  feeling  is  the  psychological  term  for  a  class  of 
mental  events,  and  it  must  not  be  confused  in  any  way  with  the  term 
used  so  variously  in  common  speech — feeling  a  touch,  feeling  cold,  feeling 
a  pin-prick,  etc.     These,  as  we  saw  in  studying  the  senses,  are  sensations. 


404  MEXTAL  FUXCTIOX 

The  feelings  proper  are  more  complex  experiences,  some  of  wliose 
characteristics  we  shall  shortly  describe;  it  is  necessary  first  to  learn 
about  feeling  in  general. 

Feeling  may  be  considered  the  primary  or  primal  aspect  of  mind.  By 
primal  here  is  meant  the  most  basal,  possibly  the  simplest  and  the  most 
closelv  related  to  the  matter  of  the  body.  Perhaps  besides  it  was  the  first 
aspect  of  consciousness  to  develop  on  the  evolution  of  dead  matter  into 
protoplasm.  In  the  new-born  infant  feeling  certainly  is  a  very  con- 
spicuous part  of  the  consciousness,  far  more  so  than  are  its  knowing 
functions.  In  the  human  fetus  (as  possibly  in  the  simplest  animals) 
feeling  more  largely  still  predominates  over  knowing  and  willing.  In  the 
human  adult  it  touches  the  personality  more  closely  than  do  these  other 
aspects  of  the  mental  process. 

Sexsatiox. — We  can  describe  feeling  in  general  best  by  taking  up 
its  elements  and  observing  what  mental  events  compose  them.  At  the 
basis  of  feeling,  indeed  of  consciousness  itself,  undoubtedly  are  sensations. 
A  sensation  may  be  defined  as  an  abstracted  aspect  of  analyzed  conscious- 
ness representing  the  activity  of  a  sense-organ.  As  to  how  it  represents 
it  we  know  absolutely  nothing.  Of  all  the  relations  and  problems  in 
physiology  the  precise  relation  between  the  material,  protoplasmic  sense- 
organ  and  its  centers,  and  the  accompanying  consciousness  seems  the 
most  insoluble.  The  description  of  the  sense-organs  and  their  actions 
in  a  previous  chapter  have  shown  how  various  are  these  end-organs  of 
the  afferent  nerves  and  how  numerous  are  the  modes  of  their  activity. 
Attempts  to  estimate  the  number  of  elementary  sensations  at  the  basis 
of  consciousness  have  been  various ;  as  accurate  as  any  other  doubtless 
is  that  of  Titchener: 

Eye 30,850  Tendon I 

(Brightness,  700;  colors,  150.)  Joint I 

Ear 11,550  Alimentary  canal  .      .      .  (?)  3 

(Tones,  11,000;  noises,  550.)  Blood-vessels ? 

Nose (?)     10,000  Lungs (?)  1 

Tongue  ....       (only?)  4  Sexual  organs 1 

Skin 3  Ear  (static  sense) 1 

Muscle 1  All  organs  (pain) 1 

These  fifty  thousand  are  the  difi'erent  qualities  of  sensation,  but  they  do 
not  for  the  most  part  represent  the  various  intensities  of  the  sensations 
(the  quantity,  so  to  say,  of  each)  and  of  course  not  the  number  or  the 
local  signs  of  the  sense-organs  which  produce  them.  From  one  point  of 
view  a  strong  sen.sation  (one  of  great  intensity)  is  a  very  (Hflerent  sensa- 
tion and  experience  from  a  weak  sensation  arising  in  the  same  end- 
organ.  For  example,  while  the  skin  may  have  only  four  sorts  of  sensa- 
tion (touch-pressure,  heat,  cold,  and  pain),  it  has  of  course  many  thou- 
sands of  end-organs  serving  these  four  senses,  and  the  experience  conu'iig 
from  each  end-organ  (as  we  have  seen)  may  be  different  from  that  of  every 
other,  especially  by  that  space-  or  locality-element  known  as  its  local  sign. 


MEXTAL  FUXCTIOX  405 

Before  we  try,  liowever  unsuccessfully,  to  understand  how  the 
"'product"  of  the  myriad  end-organs  fuse  into  the  continuum  of  conscious- 
ness, let  us  look  at  the  nature  of  a  sensation  in  general  from  the  descrip- 
tive standpoint.  It  is  true  that  a  sensation,  properly  speaking,  cannot  be 
described,  but  it  can  be  marked  off  from  the  other  aspects  of  the  mental 
process  in  a  way  which  amounts  more  or  less  to  description.  Suppose, 
then,  a  newly  born  infant  waking  from  sleep  in  a  room  l)rilliantly  lighted 
by  sunlight  entering  through  bright  crimson  window-shades.  For  a 
longer  or  a  shorter  ])eriod  this  newl^orn  infant's  consciousness  we  might 
suppose  would  l)e  largely  a  pure  sensation  of  redness.  This  redness- 
sensation  it  is  obvious  can  be  described  only  by  reference  to  similar 
experience — no  mere  words  could  ever  make  one  blind  from  birth 
realize  what  redness  is  like.  To  this  child  whose  consciousness  as  yet 
had  not  had  time  to  develop  its  various  latent  aspects,  the  red-sensation 
would  for  the  time  be  all-inclusive  and  it  would  be  essentially  a  pure 
unmixed  sensation,  namely  of  redness.  Now  suppose  an  adult  awaken- 
ing gradually  in  the  same  sun-lit  room  early  in  the  morning  after  too  few 
hours  of  sleep.  AMien  his  eyes  opened  the  sensation  of  redness  would 
more  or  less  monopolize  also  his  mental  process,  and  his  whole  conscious- 
ness might  for  a  few  seconds  be  only  of  this  one  all-pervading  redness. 
Theoretically,  then,  even  an  adult  may  have  sensations  unmixed  with 
the  other  aspects  of  mind,  "pure"  sensations.  In  fact,  however,  pure 
sensations  in  the  adult  are  both  rare  and  very  brief.  Thus,  in  the 
example  cited,  within  a  few  seconds  other  conscious  elements  would 
begin  to  fuse  into  the  sensation  of  redness,  elements  of  knowing  and  of 
willing.  The  man  would  begin  almost  at  once  to  think  and  to  intend 
or  to  wish  or  to  fear  or  to  enjoy  or  to  do  something  else  among  the  numer- 
ous possible  processes  of  his  mental  action.  The  flood  of  crimson  sun- 
light would  continue  to  pervade  his  experience,  but  previous  experiences 
with  all  their  multiform  traces  and  activities  would  have  already  begun 
to  arise  in  the  man's  memory  and  to  take  possession  of  his  mind.  He 
would  then  no  longer  experience  a  pure  sensation  in  his  mind,  but  rather 
the  usual  complex,  variously  composed  of  feeling-elements  more  or  less 
mixed  with  elements  of  cognition  and  of  will.  Thus,  then,  we  see  what 
sensation  as  such  is :  it  is  the  consciousness  corresponding  to  the  activity 
of  one  sort  of  sensory  end-organ.  Sometimes  only  one  of  these  end- 
organs  may  be  concerned  in  a  sensation,  but  often  there  are  thousands, 
as  in  the  example  given.  The  number  matters  not  so  long  as  the  result- 
ing consciousness  is  a  strictly  homogeneous  experience  of  the  sort  now 
sufficiently  suggested. 

Fusion  is  one  of  the  most  basal  operations  of  the  mental  process.  Its 
simplest  form  brings  about  the  cohesion  of  the  sensory  elements  (really 
represented  by  sense-organ  elements)  into  actual  sensations  which,  for 
the  naive  muUitude,  are  themselves  elementary.  The  trained  musician, 
the  tea-taster,  the  skilled  color-mixer,  whether  artist  or  artisan,  the  intro- 
spective psvchologist,  all  and  many  others,  have  more  or  less  the  means  of 
reducing  perhaps  even  to  their  lowest,  that  is  organic,  terms,  the  sensory 


406  •=  MEXTAL  FUXCTIOX 

complexes  given  somehow  Avholly  or  in  part  through  the  sensory  end- 
organs.  One  has  to  think  of  this  process  of  fusion  as  almost  the  chief 
underlying  activity  of  consciousness.  As  to  its  means,  nothing  is  known. 
We  see  anatomically  discrete  sense-organs  and  other  protoplasmic  units — 
we  experience  in  ourselves  the  products  of  their  fusion.  No  present 
facts  or  theories  satisfactorily  bridge  this  gap  in  our  understanding  of  our 
consciousness.  Unsupported  hypothesis  is  not  enough  in  science,  else 
we  might  perhaps  attempt  a  solution  of  the  problem  by  supposing  that 
it  is  the  general  body-protoplasm  which  represents  consciousness  rather 
than  the  nervous  system  (including  its  disparate  sense-organs)  alone. 

The  various  degrees  of  activity  of  the  sense-organs  in  the  body  imply 
many  degrees  in  the  intensity  of  the  sensations  they  represent.  Each 
sense  has  a  range  of  intensities  from  the  threshold  to  that  at  which  no 
further  increase  of  sensation  is  possible  and  the  sense-organ  is  injured. 
But  what  of  the  effects  produced  by  stimuli  below  the  threshold-intensity? 
In  the  case  of  a  frog's  gastrocnemius  muscle,  it  will  be  seen,  on  reference 
to  the  laboratory  experiments  (No.  45)  in  the  Appendix,  that  there  exists 
a  summation  in  stimuli  which  singly  are  inadequate  to  produce  a  con- 
traction. In  other  words,  if  the  threshold-stimulus  of  a  muscle  be  found 
and  then  stimuli  of  less  intensity  be  repeatedly  thrown  into  the  muscle 
a  few  seconds  apart,  contraction  finally  occurs.  The  slight  stimuli  do 
then  influence  the  muscle  and  leave  traces  in  it  which  summate  and  after 
a  while  reach  the  threshold- value  and  occasion  a  contraction.  One  sees 
the  same  thing  in  the  sensory  realm.  It  is,  for  example,  an  almost 
universal  human  habit  to  knock  repeatedly  rather  than  once  on  a  door 
when  one  would  attract  the  attention  of  those  within,  in  part  on  this 
same*  principle  of  summation.  Stimuli,  then,  below  the  threshold  do 
affect  the  organism's  protoplasm,  and  leave  some  sort  of  an  impression 
more  or  less  persistent.  This  fact,  as  we  have  seen,,  is  easily  proved  by 
actual  experiment,  and  so  proved  becomes  the  basis  of  an  important 
principle  in  the  relations  of  the  stimulus  to  the  reaction  both  psychical 
and  somatic.  It  leads  to  an  understanding,  in  a  way,  of  the  far-reaching 
phenomena  of  the  "sub-conscious"  aspects  of  the  mental  process. 

In  a  text-book  of  physiology  we  need  not  be  concerned  even  for  a 
moment  with  that  interesting  but  futile  scholastic  doubt  whether  a 
sensation,  an  aspect  of  consciousness,  can  be  said  ever  to  be  unconscious. 
We  cut  the  doubt  promptly  here,  as  in  the  chapter  on  the  senses,  by  the 
fourfold  assertion  that  it  is  a  matter  only  of  terminology;  that  "sensa- 
tion" is  not  in  all  cases  an  accurate  term,  in  so  far  as  it  usually  implies 
conscious  experience;  that  there  are  all  degrees  of  consciousness,  the 
lesser  degrees  merging  into  (neural?)  influences  which  singly  have  no 
consciousness  capable  of  being  felt;  and  finally  that  these  subconscious 
influences  constitute  the  place,  the  time,  and  the  means  wherein  the 
mental  process  fuses  into  the  other  processes  which  physiology  describes. 
What  these  influences  or  impulses  or  conditions  of  activity  are  and 
where  they  originate  we  do  not  know  completely.  We  think  we  know 
that  the  neural  maze  is  their  pathway  througli  the  body.     We  suppose 


MENTAL  FUNCTION 


407 


that  some  of  them,  mider  various  conditions  of  intensity  or  of  other 
requisites,  are  ahvays  risen  into  what  we  call  full  consciousness,  and  that 
the  others  are  meanwhile  concerned  in  carrying  on  the  vastly  complex 
processes  of  the  neuro-myo-glandular  mechanism  of  the  body.  These 
former  and  these  latter  combine  to  constitute  the  "bulk"  or  "mass"  or 
"substance"  of  the  mental  process  as  physiology  understands  it,  while 
the  sum  of  the  latter  influences  alone  constitute  what  is  known  as  sub- 

FiG.  242 


A  metaphorical  cross-section  of  the  "stream  of  consciousness."  The  shifting,  free  attentive 
consciousness  of  the  individual  may  be  aware  of  nearly  anything  on  the  earth  below  or  in  the 
heavens  above.  Beneath  it  is  the  mass  of  varied  sensation,  and  this  below  merges  into  sub- 
conscious mental  processes,  and  these  in  turn  into  the  neural  and  general  vital  energies  of  the 
body-protoplasm.  The  obstructions  and  personal  peculiarities  of  the  body  affect  markedly  all 
aspects  of  consciousness,  as  these  are  the  structures  by  which  the  mental  process  is  .supported. 
The  dependence  of  the  conscious  stream  on  the  integrity  of  the  protopla.^m  by  which  it  is 
guided  is  peculiarly  close. 


consciousness.  In  general  terms  our  total  consciousness  during  normal 
sleep  tends  to  be  of  the  subconscious  sort,  although  apparently  nearly 
always,  perhaps  always,  blended  with  attentive  consciousness  also.  We 
have  to  think  subconsciousness  as  made  up,  then,  of  "sensations"  (and 
other  mental  aspects)  which  do  not  at  the  time  occupy  the  conscious 
attention  of  the  individual,  and  this  might  serve  as  a  rude  definition 
of  subconsciousness.  (For  the  other  subcon.scious  aspects  of  the  mental 
proce-ss  see  below,  under  Willing  and  Knowing.)     The  description  of 


408  MENTAL  FUNCTION 

the  subconscious  is,  however,  as  difficult  as  its  physiology  is  important. 
E.  von  Hartmann  has  described  it  once  for  all  in  his  weighty  but 
oppressive  "Philosophy  of  the  Unconscious,"  while  numerous  students 
of  abnormal  mind,  of  the  phenomena  of  hypnosis,  of  suggestion,  and  of 
sleep,  of  multiple  personality,  etc.,  add  continually  to  the  knowledge  of  its 
influence,  and  (but  much  more  slowly)  to  that  of  its  more  precise  nature 
in  phvsiological  terms. 

The  relations  of  the  subconscious  aspects  of  mind  are  perhaps  best 
illustrated  by  the  admirable,  if  trite,  simile  of  a  stream:  Let  the  water 
of  a  deep  and  rapid  river,  then,  represent  the  sensory  mass  of  conscious- 
ness, its  rocky  bed  the  basal  organism,  its  surface  the  thin  and  changing 
focus  of  attentive  consciousness,  and  the  manifold  and  active  mass  below 
the  subconscious  parts  of  the  mental  process.  These  lower  portions 
are  not  readily  appreciated,  for  they  flow  deeply  and  more  or  less  darkly 
beneath  the  surface,  down  near  their  unexplained  channels  in  the  proto- 
plasm. On  these  lower  strata  of  the  stream  the  upper  layers  rest.  It 
is  only  the  surface  which  is  fully  realized  at  any  moment.  Any  disturb- 
ance below  (in  the  subconscious)  produces  changes  above,  while,  on  the 
contrary,  any  commotion  of  the  surface  (conscious)  portion  of  the  river 
may  influence  only  to  a  less  degree  and  less  easily  the  depths  beneath — 
especially  little  those  which  are  deepest  and  closest  to  the  bodily 
functioning.  Obstructions  in  the  minor  channels  in  this  river-bottom 
(say  an  inflamed  nerve)  produce  upheavals  not  only  in  the  mass  (the 
subconsciousness),  but  also  on  the  surface  (in  full  consciousness).  This 
stream  never  stops  so  long  as  its  banks  are  present  to  direct  and  continue 
its  movements,  but  its  foggy  surface  may  at  times  be  all  but  invisible  (as 
in  coma),  althougli  perhaps  always  in  existence.  With  the  ultimate 
destination  of  the  river  physiology  is  not  concerned  any  more  than  with 
its  primal  origin.  It  is  enough  now  if  we  realize  that  its  relations  both 
to  the  attentive  consciousness  above  and  to  the  bodily  substratum  below 
are  most  intimate — even  if  still  undefined. 

The  Feelings  and  Emotions. — As  we  have  just  seen,  in  the  adult 
mental  process  pure  sensations,  untinged  and  unexpanded  by  other 
aspects  of  mind,  scarcely  exist  as  such.  What  we  experience  mostly  are 
sensations,  feelings,  volitions,  and  cognitions  fused  together.  Feelings 
in  one  sense  and  figuratively  speaking  are  largely  made  out  of  sensations. 
The  canvas  and  the  richly  varied  pigments  of  a  beautiful  painting  are 
somewhat  like  the  sensations;  the  picture  itself,  significant  and  valual)le, 
tingling  with  life,  is  like  the  feeling  itself.  In  one  sense,  then,  the  feeling 
is  made  up  r)ut  of  the  sensations,  but  always  it  is  immensely  more,  even 
as  the  beautiful  picture  is  greatly  more  than  a  yard  of  canvas  and  an  ounce 
or  two  of  paint.  These  additional  affective  elements  come  from  the 
fusion  and  the  intcriictioiis  which  fake  j)liice  between  the  parts  of  the 
mental  function. 

Feeling  in  general  has  at  least  three  characteristics  in  addition  to  its 
V)asis  found  in  the  muscular,  joint,  glandular,  and  visceral  sensations 
underlying  and,  in  a  .sense,  causing  it.     These  three  qualities  are  some 


MENTAL  FUXCTION  409 

degree  of  excitement;  the  directing  of  the  conscious  attention  toward  the 
things  causing  the  feehng  (termed  the  object);  and  a  tone  of  pleasantness 
or  of  unpleasantness.  Another  element  of  feeling,  a  necessary  conse- 
sequence  of  the  others  named,  is  an  increased  self-reference.  The 
excitement  means  in  physiological  terms  that  the  activity  has  increased, 
and  the  element  of  attention  directed  toward  the  feeling's  object  implies 
only  that  a  new"  relation  has  been  set  up  between  some  object  or  condi- 
tion and  the  mental  process  as  a  whole.  It  is  the  tone  of  pleasantness  or 
of  unpleasantness  and  the  various  combinations  of  bodily  sensations 
which  are  the  distinctive  marks  of  the  feelings  and  emotions  (if  we 
leave  out  of  our  consideration  now  the  bodily  movements  which  actuate 
the  sensations).  These  certainly  are  the  two  elements  of  a  feeling  most 
conspicuous  to  the  person  at  the  time,  although  either  element  may  be 
always  inappreciable  in  certain  feelings  and  when  of  low  intensity  in 
many  feelings.  The  tone  of  pleasantness  or  of  unpleasantness  (as  the 
case  may  be)  of  a  feeling  or  emotion,  however,  may  be  of  almost  zero 
intensity.  Y^o  could  say  whether  even  a  violent  emotion  of  anger  or  of 
surprise,  for  example,  were  pleasant  or  unpleasant? 

The  characteristic  sensation-complex  (and  the  affective  tone)  of  the 
feeling  or  emotion  are  usually  sufficiently  well-marked  to  be  describable. 
We  find  developed  in  man  certain  fixed  sets  of  bodily  "expressive" 
reactions  or  movements  each  of  which  is  more  or  less  characteristic 
of  some  emotion.  Each  expression  is  accompanied  by  the  particular 
set  of  sensations  which  these  movements  and  strains  in  the  muscles, 
joints,  skin,  and  glands  would  inevitably  produce  in  them  through  the 
sense-organs  (James).  On  the  other  hand,  most  of  the  feelings  and 
emotions  are  either  distinctly  pleasant  or  unpleasant,  and  it  is  by  this 
criterion  that  they  are  usually  classified.  The  typical  pleasant  emotion 
is  joy,  while  a  typical  unpleasant  one  is  sorrow  or  fear.  If  one  observes 
intelligent  dogs,  apes,  savages,  or  young  children  while  experiencing 
such  emotions  as  these  it  will  be  obvious  what  the  "expression"  of  each 
of  these  emotions  is,  and  it  will  be  seen  that  each  tends  to  be  physiologi- 
cally alike  in  all  similar  animals.  In  civilized  and  cultured  men  and 
women, however, these  characteristic  "expressions"  have  been  hereditarily 
repressed,  and  the  latter  are  not  to  be  found  under  normal  conditions  in 
these  men  therefore  in  their  physiological  purity.  Even  in  such  constrained 
animals,  however,  we  can  see  that  joy  tends  to  general  expansion  and  is 
enacted  by  the  extensor  muscles  much  more  than  by  the  flexors.  Sorrow, 
on  the  contrary,  is  restricted  and  condensative,  and  "expresses"  itself 
more  largely  by  the  flexor  muscles  of  the  body.  The  smile  and  laugh  are 
the  characteristic  expression  of  joy,  but,  on  the  other  hand,  tears  flow  both 
from  sorrow  and  from  an  extreme  degree  of  mirth.  Technically,  this 
term  the  "expression"  of  an  emotion  is  misleading,  for  the  bodily  actions 
are  at  least  as  primary  as  the  sensation-feelings  accompanying  them. 

As  for  the  various  difl^erent  feeling-experiences  and  sets  of  actions, 
the  feelings  and  emotions,  they  are  numberless  ami  imclassifiable.  To 
say  that  they  are  of  fouror  five  general  sorts,  such  as  sensuous,  intellectual, 


410  MEXTAL  FUXCTIOX 

moral,  esthetic,  is  only  to  erect  wholly  artificial  barriers  between  a  multi- 
tude of  feelings  many  of  which  have  the  cliaracteristics  of  two  or  even  of 
all  of  these.  The  student  of  ethnology  will  realize  how  closely  allied  at 
their  bases  are  some  of  the  feelings,  for  example,  of  religion  and  of  sex, 
and  the  dividing  line  between  the  esthetic  and  the  sensuous  feelings  is  like- 
wise cjuite  indefinite.  The  feelings  have  not  yet  been  described  because 
so  numerous,  so  complex,  and  in  some  cases  so  indefinite.  A  few  of  the 
stronger  and  more  elaborate  of  the  emotions,  such  as  joy,  anger,  grief, 
hate,  shame,  surprise,  contempt,  have  very  well-defined  phenomena,  and 
descriptions  of  some  of  these  are  to  be  found  in  the  technical  literature 
and  monographs.  The  majority  of  the  lesser  emotions  and  the  feelings 
into  which  they  merge  have  no  such  marked  characters, bodilyand  mental,, 
and  remain  for  physiology  something  like  a  chaos  of  ill-defined  activities. 
One  principle,  however,  seems  common  to  them  all :  each  tends  to  involve 
actions  which  either  by  the  nerves  or  the  circulation  or  both  often  im- 
plicates every  portion  of  the  body.  The  bodily  aspect  of  a  feeling  or  an 
emotion,  then,  is  not  a  matter  of  activity  in  a  few  muscles  or  a  few  nerves. 
Changes  in  blood-pressure,  diffusion  in  the  central  nervous  system,, 
local  vaso-motions,  affections  of  the  alimentary,  respiratory,  muscular,  or 
glandular  systems,  involve  practically  the  whole  unified  body  more  or  less 
in  every  feeling  or  emotion  of  fair  intensity.  The  recent  work  with  the 
reflecting  galvanometer  (]\Iorton  Prince)  shows  how  intimately  related 
are  the  electrical  resistance  of  the  organism  and  affective  excitement 
even  of  the  lowest  degrees.  Such  physical  facts  open  up  wide  regions  for 
the  stiuly  of  the  relations  of  mind  and  body.     (See  also  below,  p.  418.) 

Willing. — The  second  or  willing  aspect  of  the  mental  function  is 
denoted  often  by  the  synonymous  terms  volition,  conation,  or  action. 
From  the  purely  biological  point  of  view  the  will  of  any  animal  is  basally 
its  vital  principle.  Its  will  to  live  is  the  sum  of  its  exceedingly  complex 
vital  processes,  until  by  evolution  this  somatic  phase  of  the  living  animal 
merges  into  the  psychological  aspects  of  the  will.  We  can  no  more  draw 
a  sharply  dividing  line  between  the  psychological  will  and  the  physiologi- 
cal life-movements  than  we  can  between  a  subconscious  sensation  and 
the  nervous  impulses,  etc.,  related  to  it.  Inasnuich,  however,  as  the  will 
of  an  animal,  man  for  example,  is  describable  only  through  some  sort  of 
movement,  it  is  customary  in  modem  times  to  discuss  the  will,  as  also 
the  emotions,  in  terms  of  the  actions  of  the  individual. 

From  this  point  of  view  we  speak  of  four  aspects  of  volition.  The  first 
of  these  is  the  reflex  movement.  Underlying  this  kind  of  activity  there  is 
a  mass  of  nervous  influences  for  each  one  of  the  countless  different  reflex 
actions,  while  directing  this  mass  of  sensori-motor  influences  is  the 
inevitable  motor  idea  of  the  movement.  "This  has  already  been  described 
under  the  head  of  kinesthesia  in  the  two  preceding  chapters,  and  consists 
of  the  traces  left  in  the  motor  portions  of  the  brain  by  the  numberless 
active  and  passive  movements  already  made  by  the  animal.  In  the  case 
of  this  reflex  kind  of  willing  the  motor  idea  is  subconscious:  either 
practically  unconscious  or  of  such  a  nature  as  to  occuj)y  some  portion 


MENTAL  FUNCTION  411 

of  the  attention  of  the  individual.  This  variety  or  phase  of  vohtion  is 
inherited  from  our  ancestors  and  constitutes  primarily  the  chief  part  of 
the  mental  (sensori-motor)  inheritance  of  the  infant. 

The  second  sort  of  action  thought  of  as  viill  is  the  hah'dual  voluntanj 
movement.  If  we  take  the  closure  of  the  eyelid  at  the  sudden  approach 
of  an  object  as  a  typical  reflex  volition,  a  good  illustration  of  an  habitual 
voluntary  movement  would  be  the  act  of  walking  as  it  is  performed 
by  the  adult.  This  process  is  a  reflex  movement  with  conspicuous 
conscious  voluntary  aspects.  Underlying  it  is  the  same  mass  of  nervous 
influences  present  in  reflex  movement.  In  this  case,  however,  these 
nervous  influences  are  in  larger  part  sensory.  By  this  means  they 
keep  the  conscious  individual  so  fully  aware  of  where  he  is  going  and 
what  he  is  walking  on  that  the  process  may  be  accurately  directed  and 
controlled.  In  addition,  then,  to  the  mass  of  nervous  influences  and 
sensory  impulses  (the  motor  idea)  in  habitual  voluntary  movement, 
there  are  elements  of  deliberate  attention  more  or  less  conscious.  Num- 
berless examples  of  these  habitual  voluntary  movements  will  readily 
occur  to  the  reader,  for  most  of  the  every-day  routine  actions  involving 
cross-striated  muscle  are  in  this  class.  They  are  all  essentially  voluntary 
movements  which  have  become  sufficiently  reflex  to  recjuire  less  conscious 
attention  than  formerly.     (See  Expt.  88  in  the  Appendix.) 

The  third  sort  of  will  given  us  in  terms  of  actions  are  neiv  voluntary 
movements.  Were  the  student  of  medicine  to  undertake  to  artistically 
engrave  an  intricate  monogram  on  a  silver  vase,  he  would  have  in  his 
experience  a  striking  illustration  of  a  new  voluntary  movement.  If  we 
analyze  this  experience  physiologically,  we  shall  find  in  it  the  same  mass 
of  nervous  influences  and  sensory  impulses  that  were  present  in  the 
habitual  voluntary  movement.  In  the  present  case,  however,  the  ner- 
vous influences  are  almost  all  accompanied  by  clear  kinesthetic  sensa- 
tions. Besides  this,  there  is  required  a  large  degree  of  deliberate  atten- 
tion to  the  movements  and  strains  of  the  arms  and  trunk,  and  in  addition 
to  this  a  continually  exerted  choice  that  the  movements  shall  continue  in 
just  the  right  way.  In  psychological  terms  we  have  here  the  motor  idea 
coming  into  the  brain  from  these  exclusively  voluntary  muscles  plus 
forced  and  carefully  directed  attention  plus  deliberate  choice  to  continue. 
All  of  these,  it  will  be  observed,  are  highly  conscious  processes.  It  is 
only  in  this  third  sort  of  volition  that  the  aspects  of  will  as  commonly 
known  to  the  average  man  become  conspicuous.  In  such  movements 
as  these,  made  by  the  motor  nerve-centers  and  the  cross-striated  muscle 
often  under  great  stress  of  effort  and  continued  only  by  great  fatigue  and 
even  pain,  every  man  would  recognize  the  exertion  of  his  will.  The 
other  two  aspects  of  will  which  we  have  just  described  are  volitions  from 
a  somewhat  more  biological  point  of  view. 

The  fourth  and  last  sort  of  will  which  we  need  to  briefly  describe  is 
that  which  may  be  best  perhaps  called  choice,  or  free-choice  decision. 
It  is  almost  wholly  about  this  aspect  of  willing  that  our  philosophical 
ancestors  talked  and  wrote  so  much  in  the  century  before  the  last.     In 


412  MEXTAL  FUXCTIOX 

those  days  the  discussions  (mostly  with  a  religious  bearing)  concerning 
volition  were  almost  wholly  arguments  as  to  the  "freedom"  of  the  will, 
as  to  whether  the  individual  was  free  to  determine  alternatives  for  himself 
independently  of  all  else.  Into  this  discussion,  still  undecided  from  the 
biological  point  of  view,  we  have  no  idea  of  going  here  more  than  to 
suggest  that  every  normal  personality  believes  unalterably,  whatever 
he  may  say  and  argue,  that  his  will  is  free.  The  whole  system  of  human 
justice  rests  upon  this  intuitive  certainty.  Physiologically,  however,  it 
is  very  difficult  to  define  any  basis  for  this  sort  of  willing.  There  may 
be  a  bodily  movement  present  or  apparently  there  may  be  none  in  any 
particular  determination  of  choice.  ^^Qien  a  muscular  movement  is 
present,  there  are  motor  ideas  and  motor  nerve-impulses  accompanying  it. 
These  perhaps  would  not  actually  contract  the  muscles  but  only  change 
their  tonus.  T\Tien  the  choice  is  wholly  a  matter  of  thought,  the  motor 
side  of  the  process  is  probably  located  chiefly  in  the  mechanism  of 
speech  (see  pages  394  and  420). 

The  normal  willing-process  in  general,  comprising  a  stimulus  and  a 
motor  reaction  thereto,  requires  an  appreciable  and  easily  measurable 
period  of  time.  As  any  one  familiar  with  the  processes  of  the  complicated 
neuro-muscular  system  would  expect,  the  time  differs  for  every  combi- 
nation of  events.  Thus,  if  electrical  apparatus  be  arranged  so  that  some 
part  of  the  skin  is  to  be  touched  and  the  reactor  is  to  press  an  electrical 
key  as  soon  as  he  can  after  he  feels  the  touch  (the  type  of  all  determina- 
tions of  reaction-time),  the  time  is  longer  when  it  is  the  toe  that  is  touched 
than  when  it  is  the  ear.  It  is  shorter  to  pressure  than  to  light,  but  longer 
to  sound  than  to  pressure.  If  the  reactor  has  to  decide  which  of  two 
possible  sorts  of  stimuli  it  is  (as  for  example  red  or  blue)  before  react- 
ing, the  time  is  longer  yet.  It  is  longer  to  weak  stimuli  than  to  strong; 
becomes  shorter  by  practice;  is  longer  in  dull  persons  than  in  bright 
persons,  etc.  By  this  general  means  many  of  the  relations  and  pro- 
cesses of  mental  function  have  been  studied  and  thousands  of  exact 
time-measurements  made  with  the  chronoscope,  measuring  accurately 
to  the  thousandth  of  a  second.  Some  individuals  are  accurate  and 
quick,  some  accurate  and  slow,  some  inaccurate  and  quick,  and  some 
inaccurate  and  slow.  Some  persons  recognize  the  stimuli  quickly  but 
react  slowly,  and  others  are  quick  of  muscle  but  slow  of  sense.  In 
general  terms  the  sm.aller  a  muscle  the  more  quickly  it  reacts.  Habit, 
however,  has  more  to  do  with  the  shortness  of  the  reaction-time  than 
anything  else:  for  example,  one  reacts  sooner  with  the  index  finger  than 
with  the  fifth.  It  is  not  difficult  by  practice  (habit)  to  make  a  voluntary 
movement  practically  automatic  by  continued  repetition  under  constant 
conditions;  the  reaction-time  then  is  also  much  shortened. 

On  the  average  a  person  touclied  on  the  liaiid  can  move  his  finger  in 
about  0.110  second;  if  the  stimulus  be  received  through  Uie  eyes,  in  al)out 
0.180  second;  and  if  through  the  ears,  in  about  0.120  second.  If  the 
reactor  be  thinking  of  the  stimulus  rather  than  concentrating  his  attention 
on  the  movement  to  be  made,  the  reaction  to  light  is  about  0.270  second 


MENTAL  FUNCTION  413 

(instead  of  0.180  second).  This  indicates  the  extent  to  which  the  inertia 
of  muscle  (and  nerve?)  may  be  reduced  by  hokHng  the  organ  in  the 
utmost  tonic  readiness.  If  one  has  to  discriminate  between  colors  in 
the  stimuhis,  the  average  reaction-time  is  over  0.300  second,  while  recog- 
nition of  a  printed  letter  or  short  word  requires  0.020  second  longer.  It 
is  found  that  in  general  a  quantitative  choice  or  judgment  and  choice 
(between  two  stimuli,  that  is,  of  the  same  sort  but  dirterent  intensities) 
is  about  0.060  second.  Wlien  it  has  become  automatic  the  discrimina- 
tion between  two  colors  may  require  no  more  than  0.011  second,  quality- 
difference  being  more  quickly  perceived  than  quantity-difference. 

These  reactions,  it  will  have  been  observed,  are  under  conditions 
which  represent  the  ordinary  will-actions  of  every-day  life  reduced  for 
exact  measurement  to  their  very  lowest  terms.  It  has  been  objected 
(as  by  Cattell)  that  experiments  on  fragments  of  actual  will-process  so 
small  as  these  have  comparatively  little  practical  use,  however  important 
thev  may  be  theoretically.  The  movements  of  every-day  life  are  im- 
mensely complicated  in  every  way,  and  fuse  together  so  as  to  make  a 
medley  of  activities  in  muscle  and  nerve-center  far  beyond  our  present 
power  of  comprehension  or  of  measurement.  Our  consciousness  derived 
from  them  is  at  least  correspondingly  complex. 

Habit  and  Instinct. — An  instinct  is  essentially  an  hereditary  im- 
pulsive and  unstudied  habit  concerned  in  the  biological  interests  of  the 
indivitlual  or  of  the  race.  It  is  a  complex  variety  of  habit  which  needs 
but  little  separate  discussion  here  especially  because  the  many  varied 
instinctive  activities  have  in  them  only  a  minimum  of  attentive  con- 
sciousness. The  mechanism  by  which  the  instincts  are  so  carefully 
bequeathed  from  parent  to  offspring  century  after  century  is  part  of  the 
vital  faculty  hidden  in  the  body-protoplasm.  Our  search  must  be  briefly 
into  the  nature  of  habit,  in  which  instinct  partakes. 

Habit  is  a  motion  of  very  general  significance  in  nearly  all  aspects  of 
the  world.  It  means  in  the  widest  usage  the  adaptation  of  a  material 
to  the  activities  of  that  material,  and  is  therefore  by  no  means  confined 
to  organisms.  Rain-water  running  down  a  hill-side  gradually  forms 
grooves  in  the  soil  and  leads  to  the  formation  of  habitual  water-courses. 
XVild  animals  make  paths  through  the  forest  to  the  ponds  and  springs. 
Complicated  machines  run  much  better  after  a  certain  Uinount  of  use 
has  adapted  the  adjacent  moving  parts  to  each  other  and  into  a  habit 
of  normal  usage.  In  protoplasm,  probably  the  most  complex  of  sub- 
stances, this  universal  adaptation  is  more  complicated  and  consists  not 
only  of  action  but  of  reaction  not  possible  in  inorganic  machines.  Owing 
to  the  extreme  plasticity  of  the  material,  organisms  can  work  in  a  host  of 
different  ways,  each  making  an  impression  on  the  mechanism  in  propor- 
tion to  the  number,  the  frequency,  and  the  vigor  of  the  activities  con- 
cerned. Thus,  right-handedness  unfortunately  becomes  a  settled  and 
almost  unbreakable  habit  in  most  persons'  organisms  before  five  years 
have  passed  and  simply  because  during  the  development  of  voluntary 
movement  the  use  of  the  left  arm  is  neglected.     What  the  traces  are 


414  MEXTAL  FUNCTION 

which  determine  the  habitual  usage  in  the  body  remains  to  be  discovered. 
We  have  to  think  of  them,  however,  as  actual  traces  in  the  protoplasm 
especiallv  of  the  nervous  system,  but  perhaps  in  part  also  of  the  muscles 
and  other  tissues.  This  is  witnessed  by  the  larger  size  of  the  whole 
right  side  in  right-handed  persons.  The  logical  limit  of  this  process  of 
habituation  is  to  be  seen  in  the  so-called  "automatic"  organs:  glandular 
epithelium,  the  heart,  the  ureters,  the  musculature  of  the  intestines,  etc. 
The  lesser  degrees  of  it  are  known  to  all  in  the  thousand  physiological 
minor  habits  of  every-day  life. 

Of  essentially  the  same  nature,  doubtless,  are  the  so-called  mental 
habits  of  feeling,  of  willing,  and  of  thinking. 

The  function  of  habit  is  almost  obvious.  By  means  of  this  continually 
greater  ease  in  the  performance  of  an  action,  "mental"  or  "bodily," 
those  movements  which  necessarily  frequently  recur  become  more  and 
more  reflex  or  automatic.  In  this  way  the  voluntary  aspects  of  the 
brain  are  relieved  of  directing  a  host  of  mechanical  operations  that  are 
biologically  necessary  but  which  would  needlessly  consume  a  large 
amount  of  the  time  and  attention  "of  the  cortex."  The  central  nervous 
svstem  is  thus  left  free  to  learn  new  things,  to  progress  in  capability,  and 
to  assist  in  the  development  of  civilization  and  of  culture. 

Knowing. — The  last  of  the  three  chief  aspects  of  the  mental  process 
is  the  faculty  of  knowing  objects,  qualities,  relations,  and  so  on,  outside 
or  inside  the  organism.  Spionyms  for  this  process  are  cognition, 
ideation,  and  intellection.  In  the  most  general  sense  this  aspect  of  the 
stream  of  consciousness  may  be  called  the  formation  of  ideas.  An 
idea  may  be  roughly  defined  as  a  mental  image  of  any  object  whatever 
outside  or  inside  the  mind.  In  this  definition  the  expression  "object" 
is  used  in  the  very  general  sense  which  includes  not  only  the  so-called 
material  things  but  the  qualities  and  relations  of  a  purely  abstract  nature. 

The  physical  correspondents  of  this  cognitive  process  are  narrower  in 
bodily  range  than  are  those  of  feeling  and  of  willing.  In  general  terms 
we  may  denote  them  as  chiefly  the  movements  and  reactions,  nervous 
and  muscular,  which  are  employed  in  any  mode  of  expressing  language. 
The  physical  basis  of  cognition,  in  other  words,  is  mainly  the  neuro- 
muscular mechanism  of  psychical,  spoken,  written,  pictured,  and  manual 
speech. 

Analysis  of  the  knowing  aspect  of  mind  gives  us  several  steps  in  a 
process  which  is  continually  some  sort  of  fusion.  We  may  distinguish 
the  fundamental  process  of  sensation,  and  upon  that  as  a  basis  "the 
mind"  conducts  the  various  operations  of  perception,  conception,  under- 
standing, and  reason.  The  means  by  which  this  very  complicated  fusion 
accomplishes  the  interaction  and  development  of  the  original  sensation- 
mass  is  hidden  from  us  in  the  largely  unknown  relations  of  the  nerve- 
paths  especially  of  the  brain.  That  these  fuse  in  some  way  so  as  to 
elaborate  the  higher  products  of  the  knowing  faculty,  there  is  litde  doubt. 

The  things  which  are  known  in  cognition  are  of  two  general  sorts: 
things  "outside"  and  those  "inside"  the  mind.     A  chair,  for  example. 


MEXTAL  FL'XCTIOX  415 

which  we  look  at  standing  before  us  and  think  of,  is  ol)viously  an  ol)ject 
outside  the  mind,  while  if  we  then  close  our  eyes  and  observe  our  memory- 
image  of  the  chair  just  seen  we  are  evidently  cognizing  an  object  "inside" 
our  consciousness.  Further  consideration  of  the  former  of  these  processes, 
however,  shows  us  that  when  we  looked  at  the  chair  what  we  really  expe- 
rienced was  not  a  chair  but  a  sensation  of  seeing,  and  that  what  we  thought 
of  in  both  cases  was  a  curious  sort  of  mental  representation  of  a  chair. 
Thus,  we  see  that  in  both  cases  in  reality  what  we  know  is  "inside"  the 
mind,  although  we  appear  clearly  enough  to  see  the  chair  itself  or  its  mental 
representative  at  will.  This  is  the  view  of  the  thoughtless,  the  naive 
realism  of  the  mass  of  mankind,  and  the  view  also,  we  may  see,  assumed 
to  be  the  better  for  physiological  purposes  though  all  the  while  believed 
in  reality  to  be  a  false  view  and  one  which  is  philosophically  misleading. 
Tiius,  we  may  go  on  and  describe  cognition  as  a  process  which  knows 
(at  different  times)  objects  both  outside  the  mind  and  inside  the  mind. 
It  will  appear  shortly  that  without  the  inside-the-mind-object  process 
the  outside-the-mind-object  process  would  give  us  no  knowledge  worthy 
of  the  name.  The  sensations  might  enter  the  mind  from  objects,  but 
without  the  internal  process  they  would  be  of  little  or  no  use  as  knowl- 
edge. We  might  then  have  knowledge  of,  but  not  knowledge  about,  the 
objects. 

First,  then,  as  to  the  process  of  knowing  objects  outside  the  passing 
current  of  consciousness.  To  make  this  clear  w^e  shall  have  to  consider 
sensation,  perception,  and  conception.  These  are  the  different  aspects 
and  degrees  of  this  fusion-process  which  is  in  itself  single  and  devoted  to 
the  sole  end  of  making  the  conscious  animal  (man  in  this  case)  familiar 
as  may  be  with  the  parts  of  his  environment.  It  will  be  seen  that  on  this 
process  almost  the  whole  fabric  of  language  and  so  of  civilization  itself 
depends. 

Sensation  has  already  been  discussed  sufficiently  for  our  physiological 
purpose.  AVe  have  seen  how  various  are  the  sorts  and  shades  of  the  sen- 
sations; that  they  are  the  simplest  elements  of  consciousness,  coming 
closest  to  the  physical  forces  of  the  environment  and  to  the  physical 
protoplasmic  basis  of  mind;  that  they  represent  the  environment  to  the 
individual  only  to  a  slight  extent,  being  largely  subjective  in  nature;  that 
they  fuse  together  in  large  numbers  for  the  most  part  so  as  to  be  indis- 
tinguishable as  units;  that  they  are  hardly  ever  experienced  in  their  pure 
state,  being  always  mixed  with  the  other  mental  aspects  (feeling  and 
will)  in  greater  or  less  proportions;  and  that  it  is  proper  to  consider 
that  the  mass,  so  to  say,  of  the  sensation-stuff  constitutes  the  subcon- 
scious part  of  the  mental  process,  close  "down"  among  the  nervous 
impulses  and  possibly  the  other  protoplasmic  activities.  The  sensations 
represent  the  energy  of  the  environment  acting  against  the  energy  of  the 
animal,  and  it  is  on  this  account  perhaps  that  they  are  so  little  objective, 
that  as  sensations  merely  they  tell  so  little  about  the  qualities  of  objects. 

Perception. — Sensation  is  essentially  subjective  in  nature,  while 
perception  is  inherently  objective.     Let  us  revert  to  our  former  illustra- 


416  MEXTAL  FUNCTION 

tion  of  the  crimson  light  we  used  in  discussing  sensations  (page  405). 
This  might  flood  oin-  consciousness  as  a  sensation  of  redness  but  techni- 
cally would  be  perceived  only  when  we  had  awakened  enough  to  realize 
it  as  an  objective  quality  or  thing  in  the  objective  world  affecting  our- 
selves as  subjects.  This  objectivity  of  perception  is  one  of  the  marvels 
of  consciousness.  To  the  thoroughly  naive  mind,  it  is  the  basal  property 
of  the  knowing  "faculty."  Even  in  thought  in  which  the  subject  knows 
objects  within  the  mind  the  objectivity  of  consciousness  is  at  least  as 
conspicuous  a  quality  as  is  its  subjectivity.  It  is  one  of  the  powers  of 
the  mental  process  that  it  can  perceive  objects  outside  itself  as  well  as 
parts  of  itself. 

Besides  the  objectivity  of  perception  its  leading  characteristic  perhaps 
is  its  process  of  synthesis  or  fusion.  In  our  study  of  the  sense-organs 
a  conspicuous  fact  always  was  the  smallness  and  the  multitude  of  the 
individual  sense-organs  (considering  the  rods,  cones,  and  fibers  of  the 
membrana  basilaris  separate  organs).  Not  only  are  the  sensations  from 
these  put  together  by  the  mental  process  in  perception,  but  also  the 
unlike  sensations  from  different  classes  of  sense-organs.  When  we  per- 
ceive a  flower  we  may  perceive  not  only  color  and  form  but  odor  and 
perhaps  its  softness  and  coldness  and  stickiness  and  taste  of  sweetness. 
By  all  these  means  and  more  at  once  we  may  obtain  a  percept,  as  it  is 
called,  of  a  lily.  Various  sorts  of  sensations  have  been  thereby  combined 
into  a  representation  in  our  mmds  of  a  particular  lily.  To  explain  this 
marvellous  process  is  at  present  quite  beyond  us,  unless  indeed  we  be 
content  to  suppose  that  it  is  accomplished  by  the  close  association  or 
fusion  of  sensory  impulses  in  the  brain. 

Conception. — If  our  knowing  "faculties"  went  no  farther  and  were 
no  more  complex  than  perception,  civilization  would  never  have  evolved 
even  as  far  as  it  has.  Speech  would  have  been  undreamed  of,  as  it 
probably  is  still  among  the  brutes.  Perception  in  some  way  connects 
consciousness  with  particular,  individual  objects  or  groups  of  objects, 
thus  giving  us  a  mental  image  of  them.  Conception  goes  much  farther. 
It  picks  out  the  characteristic  qualities  and  relations  of  objects,  combines 
and  fuses  them,  and  leaves  us  possessed  of  a  general  idea  of  the  object 
or  of  its  qualities  and  relations  by  which  a  similar  one  can  again  be  known. 

The  concept  is  then  tiie  product  given  us  by  the  process  conception, 
the  nature  of  which  is  best  indicated  by  an  example  which  will  bring  out 
how  it  differs  from  perception.  Perhaps  we  can  do  no  better  than  to 
use  our  old  illustration  of  a  black-painted  wooden  chair  standing  before 
us  V>ut  never  perceived  by  us  before.  How  do  we  know  this  chair? 
Only  through  our  senses,  certainly.  Only  because  the  color  of  the  object 
differs  from  that  of  its  background  more  or  less,  vision  shows  us  its  shape 
and  size  and  (indirectly  perhaps)  that  it  occupies  space  and  is  not  a 
painted  image  on  a  screen.  This  last  is  inference  merely,  for  a  suffi- 
ciently cunning  artist  might  paint  it  on  a  screen  so  as  to  quite  deceive  us. 
If  we  go  up  and  touch  the  chair  we  shall  find  it  hard ;  if  we  saw  off  one  of 
its  legs  we  shall  see  that  it  is  made  of   wood,  screws,  etc.,  of  certain 


MEXTAL  FUXCTIOX  417 

forms  and  colors;  if  we  examine  this  wood  with  a  microscope  we  shall 
see  its  structnre;  if  we  lift  tlie  chair  we  shall  find  it  of  a  certain  weight, 
etc.  It  is  only  simple  facts  like  these  that  perception  by  the  senses  gives 
us,  although  the  facts  as  to  an  object  may  be  numerous  to  almost  any 
conceivable  extent.  We  all  really  know  much  more  about  this  black 
wooden  object,  however,  than  our  perception  could  ever  give  us.  In  the 
first  ])lace  we  know  what  a  chair  is,  an  object  to  sit  on,  and  that  it  is 
called  in  English  a  "chair;"  we  know  perhaps  how  it  was  made,  about 
how  much  it  cost,  how  much  it  is  worth,  that  it  would  burn,  float  if 
thrown  into  a  pond,  hurt  us  if  we  ran  against  it,  be  too  low  for  a 
young  child  at  table,  etc.  Furthermore,  more  or  less  unconsciously, 
perhaps,  we  compare  it  with  other  chairs  in  some  or  many  of  the  respects 
which  pertain  to  chairs.  We  are  perceiving  only  one  chair,  this  one,  but 
we  have  in  mind  all  the  time  more  or  less  unconsciously  many  of  the 
chairs  we  have  seen,  bought,  used,  broken,  heard  of,  read  of,  and  told 
about.  In  short,  w^e  all  have  in  our  minds  a  general  idea,  notion,  con- 
cept, expressed  in  English  print  and  speech  by  the  symbolic  characters 
chair.  The  parts  of  this  concept  chair  in  the  minds  of  each  are  many, 
and  they  were  derived  from  very  many  sources.  Each  person's  concept 
of  chair  differs  theoretically  from  that  of  every  other  according  to  the 
percepts  and  the  concepts  which  have  united  and  fused  together  to  form 
each  one's  concept.  If  one  of  us  is  an  artist,  he  knows  chair-concept  in 
one  way;  if  one  is  a  furniture-dealer,  in  another  way;  if  one  be  a  lover  of 
ease,  in  another  way;  if  one  be  cold  for  want  of  fuel,  possibly  in  still 
another  way;  and  so  on  without  end.  Each  of  us,  then,  has  a  notion  of 
chair  in  his  mind  provided  he  ever  saw  one  or  a  picture  of  one,  or 
heard  of  one,  or  read  of  one  before.  Yet  each  of  our  chair-concepts 
is  different  from  every  other. 

This  then  is  the  process  of  conception :  the  abstraction  of  the  qualities, 
characteristics,  relations,  categories,  uses,  etc.,  of  objects,  real  or  ideal,  and 
the  combination  of  these  qualities,  relations,  etc.,  into  general  notions. 
Only  because  of  "the  divine  gift  of  speech"  was  this  abstraction  and 
conceptualization  possible — man  gives  a  name  to  a  thing,  and  a  concept 
of  it  becomes  forthwith  attainable  for  all  men's  use.  In  the  name  of  an 
object  is  epitomized  for  us  the  key  by  which  we  can  recall  the  details, 
qualities,  relations,  etc.,  which  for  each  of  us  make  up  the  concept  of 
that  oV)ject. 

Besides  concepts  of  objects  there  are  concepts  of  every  sort  of  quality, 
relation,  use,  etc.  These  fused  together  make  up  our  knowledge 
of  life.  Each  of  us  has  in  his  mental  process  not  only  concepts  of  cjuality, 
but  concepts  of  relation  of  innumerable  sorts,  of  shape,  weight,  hardness, 
porosity,  value,  perceptibility,  inflammability,  salability,  usefulness, 
space,  causality,  reality,  infinity,  etc.  All  these  and  many  other  sorts 
of  concept  have  united  to  partake  in  our  knowledge  of  the  world  and  all 
within  and  around  it  and  above  it.  Our  knowledge  is  in  terms  of  con- 
cepts and  not  in  terms  of  percepts.  A  farm-hand,  for  example,  sees 
more  blades  of  grass  in  a  day  of  haying  than  a  city-child  might  see  in 
27- 


418  MEXTAL  FUXCTION 

its  lifetime,  yet  if  the  child  were  to  study  botany  or  vegetal  physiology  a 
week  she  might  know  more  about  blades  of  grass  than  the  farmer  would 
learn  in  fifty  years  of  raising  and  curing  them.  The  farmer  would  have 
acquired  an  enormous  perceptual  knowledge  of  blades  of  grass,  and 
the  student  some  conceptual  knowledge  about  blades  of  grass.  For 
almost  every  purpose  the  knowledge  about  is  worth  more  than  the 
knowledge  of. 

UxDERSTAXDiXG  Can  be  described  only  in  the  same  way  as  we  have 
suggested  the  fusion-process  in  conception.  This  indescribable  multi- 
tude of  concepts  which  the  human  adult  of  average  intelligence  has  some- 
how stored  in  his  brain  combine  and  interact  and  develop  what  we  call 
the  understanding  of  things.  As  the  material  of  this  marvellous  process, 
every  man  has  concepts  of  a  multitude  of  different  kinds  of  objects  rang- 
ing from  his  collar-button  to  the  sublimest  notions  of  Ultimate  Reality. 
He  has  stored  away  in  his  nerve-paths  concepts  almost  without  end. 
These  in  some  way  fuse  together  in  his  mind  and  brain  and  give  him  an 
understanding  of  the  facts  and  principles  on  which  our  human  life  is 
conducted.     (See  also  Expt.  88  in  the  Appendix.) 

The  Reasox. — A  very  perfect  s\'nonym  of  the  term  reason  is  the 
expression  common  sense.  It  means  more  than  a  large  store  of  varied 
concepts,  and  much  more  even  than  understanding,  for  it  indicates  our 
capability  of  so  uniting  the  elements  of  the  understanding  as  to  produce 
new  aspects  of  things  and  to  develop  new  truths  about  the  relations  of 
objects.  In  no  one  of  the  human  mental  faculties  do  the  mass  of  men 
differ  more  than  in  their  gifts  of  reason .  ]\Iany  have  good  understandings 
of  essential  principles  who  seldom  combine  their  energies  in  new  ways  so 
as  to  produce  new  results.  This  reasoning  process  is  the  highest  and 
most  advanced  of  the  human  mental  functions. 

The  physical  Vjasis  of  the  understanding  and  the  reason  is  to  be  sought 
in  the  same  process  of  neural  fusion  which  we  have  seen  everywhere 
present  in  desci'ibing  the  stream  of  consciousness.  The  products  of  the 
understanding,  the  multitude  of  concepts,  and  the  percepts  interact 
to  produce  mental  products  which  are  entirely  new,  of  large  value  in  the 
conduct  of  personal  and  social  life  and  in  the  advancement  of  the  world. 

The  Relations  of  Body  and  Mind. — We  liave  now  suggested  in  a  very 
brief  and  inadequate  way  some  of  the  facts  which  can  be  observed  on 
introspection  as  to  the  stream  of  consciousness  of  any  normal  human 
individual.  As  has  been  sufficiently  emphasized,  this  stream  is  a  process 
and  in  no  sense  a  substance.  Tlie  other  chapters  of  the  book  describe 
in  somewhat  more  detail  the  bodily  processes,  the  stream  of  material 
movements.  These  last  are  no  more  substantial  than  the  others,  although 
they  continually  have  reference  to  something  that  we  call  the  body 
which  appears  to  us  to  be  substantial,  l^he  mental  process  is  a  series 
of  movements  in  consciousness.  The  bodily  process  is  no  less  a  series 
of  movements  in  "matter."  Our  next  inquiry  very  briefly  refers  to  the 
relations  between  these  two  .series  of  movements  which  continue  as  long 
as  life  endures.     We  shall  keep  as  far  as  possible  from  the  ultimate 


MENTAL  FUXCTIOX  419 

metaphysical  relation  of  these  two  series,  for  our  entire  object  is  to  point 
out  some  of  the  ahnost  obvious  facts  of  their  relationship. 

Before  doino;  that,  however,  we  mav  merelv  mention  some  of  the  theories 
of  this  association.  These  are  of  three  sorts,  two  of  which  are  monistic 
theories  and  one  dualistic  at  least  for  scientific  purposes.  The  theory 
of  pure  idealism  maintains  that  the  conscious  series  is  the  real  one  and 
that  in  some  incomprehensible  way  the  bodily  series  is  but  an  aspect  of 
consciousness.  The  opposed  hypothesis,  now  clearly  given  up  by 
philosophy  as  a  living  belief,  is  the  materialistic  point  of  view,  namely, 
that  the  conscious  process  is  only  an  epiphenomenon  of  the  bodily  life, 
the  product  of  the  activity  of  protoplasm.  The  dualistic  theory  of  the 
relations  of  body  and  mind  supposes,  at  least  for  scientific  purposes,  that 
there  are  two  kinds  of  series  running  along  always  just  side  by  side  but 
of  essentially  different  natures.  When  these  two  series  are  postulated 
as  entirely  independent  of  each  other,  we  have  the  theory  of  psycho- 
physical parallelism.  Wlien  they  are  assumed  to  be  continually  inter- 
acting, we  have  the  theory  of  interaction. 

Some  biologists  have  supposed  that  only  man  was  conscious,  others 
that  the  mental  process  has  its  basis  only  in  the  nervous  system,  and 
others  still  that  all  protoplasm  has  consciousness  as  part  of  its  life.  If, 
furthermore,  there  be  a  few  who  suppose  that  consciousness  is  attached 
to  the  whole  creation,  it  is  no  affair  of  ours  in  this  connection,  but 
concerns  rather  the  speculations  of  philosophy. 

We  may  perhaps  best  suggest  a  few^  of  the  most  obvious  relationships 
of  mind  and  body  in  addition  to  those  already  intimated  above,  if  we 
take  up  in  turn  the  three  aspects  of  the  mental  process,  feeling,  willing, 
and  knowing.  Far  from  attempting  to  say  how  mind  and  body  are 
related,  we  only  mention  some  of  the  instances  in  which  a  relation  is 
especially  apparent. 

In  the  aspect  of  feeling,  willing,  and  knowing  which  we  call  sensation 
it  is  clear  in  what  way  the  bodily  mechanism  is  concerned.  In  the  chap- 
ter before  the  last  we  studied  the  sense-organs.  We  saw  that  in  every 
case  physical  force  of  some  sort  impinges  on  these  thousands  of  sense- 
organs  on  the  surface  and  in  the  interior  of  the  body,  and  that  the  nervous 
impulses  actuated  by  these  movements  in  the  afferent  end-organs  go  as 
influences  into  the  central  nervous  system.  In  every  case,  moreover, 
whether  we  can  define  it  accurately  or  not,  such  impacts  are  followed  by 
reactions  in  the  central  nervous  system  and  efferent  nerve-influences 
stream  outward.  There  is  little  doubt  at  the  present  time  that  this 
complicated  and  multifarious  maze  of  nerve-impulses  going  and  coming 
everywhere  through  the  body,  forms  the  "basis"  of  the  mental  process. 
Some  of  these  nervous  influences  are  probably  directly  and  intensely 
conscious  to  the  individual,  but  of  the  others  he  knows  nothing  directly. 
Inasmuch  as  sensation  (based  on  these  influences)  is  a  conspicuous  part 
in  almost  every  mental  process,  we  have  here  a  chief  respect  in  which 
the  body  and  the  mind  are  related. 

In  the  mental  process  known  as  feeling  and  emotion  we  have,  as  it 


420  MENTAL  FUXCTIOX 

were,  summarized  for  us  this  conspicuous  mass  of  afferent  and  efferent 
nerve-impulses  representing  much  of  the  stream  of  consciousness.  xA.s- 
we  saw  in  discussing  these  aspects  of  mind,  every  well-defined  feeling 
and  every  emotion  has  as  an  essential  part  of  itself  a  complex  of  move- 
ments within  the  range  of  the  efferent  nerve-impulses.  These  are  largely 
muscular  contractions  and  strains  and  changes  of  tone,  but  they  are  in 
part  also  innervations  of  epithelium.  Preceding  all  these  we  have  to 
suppose  a  somewhat  corresponding  multitude  of  afferent  nerve-impulses 
coming  from  sense-organs  or  perhaps  only  from  portions  of  the  brain  or 
the  spinal  cord.  Altogether  these  represent  every  portion  of  the  feeling 
aspect  of  consciousness  through  bodily  movements  and  strains,  either 
molar  or  molecular.  These  movements  and  impulses  it  is  the  business 
of  psychology  to  define  and  describe  much  more  in  detail  than  has  yet 
been  done  save  in  the  case  of  three  or  four  emotions. 

In  the  phase  of  consciousness  which  we  call  volition  the  bodily 
accompaniments  may  be  no  less  universal  than  in  feeling.  Here  too 
are  concerned  the  multitude  of  afferent  impulses  from  the  sense-organs 
which  determine  especially  the  reflex  aspects  of  will,  while  the  other  side 
of  the  nervous  arc  is  concerned  with  the  vegetative  musculature,  although 
it  may  involve  any  muscle  in  the  body.  The  actions  which  are  classed 
physiologically  as  voluntary  or  deliberate  probably  lack  these  afferent 
impulses  in  some  degree,  and  from  the  fusing  process  perhaps  in  the 
cortex  of  the  brain  impulses  pass  downward  which  actuate  the  cross- 
striated  muscles  as  well  as  those  of  the  smooth  variety.  The  accom- 
paniments of  the  willing  process  are  physiologically  of  two  phases, 
actuating  and  inhibitory,  but  these  alike  doubtless  involve  nerve-currents 
passing  to  or  from  nerve-centers.  In  the  determination  of  choice  we  can 
point  out  the  least  of  bodily  concomitance.  Morat  supposes  that  there 
is  a  continual  circulation  of  nerve-currents  in  the  cortex,  and  that  these 
in  some  way  accumulate  force  which  the  individual  uses  in  typically 
voluntary  movements. 

In  cognition  the  bodily  accompaniments  are  probably  as  before  the 
sensation-mass  represented  by  almost  universal  nerve-impulses.  Be- 
sides these  there  may  be  an  ill-understood  process  of  fusion  in  the  intri- 
cate maze  of  the  cerebral  paths.  Besides  this  general  relationsliip, 
however,  the  entire  mechanism  of  speech  represents  the  intellectual 
functions.  When  a  man  thinks  clearly,  he  thinks  only  in  terms  of  words, 
usually  either  spoken  or  written.  AVhen  a  subject  in  the  laboratory  is 
asked  to  pick  out  from  one  hunch'ed  the  ten  chance  ink-blots  most  like 
a  certain  one  shown  to  him,  he  cannot  do  so  ordinarily  without  having 
a  clear  notion  of  the  similarities  in  verbal  terms  in  his  mind.  When 
one  thinks,  it  is  likely  that  the  brain  sends  out  the  same  impulses  that  it 
would  send  out  to  the  muscles  if  these  words  were  spoken.  The  intellect, 
moreover,  does  not  develop  normally  if  speech  of  every  kind  is  by  any 
means  prevented.  In  general,  then,  ideation  is  impossible  without  the 
kinesthetic  impulses  and  motor-innervations  which  form  this  physio- 
logical basis.  Many  of  these  innervations  are  subconscious,  but  they 
may  not  less  effect  the  mind  on  that  account. 


MEXTAL  FUNCTION  421 

If  there  is  a  speech-center,  then,  in  the  brain,  it  is  not  because  the  in- 
tellectual processes  involve  only  this  small  area  of  the  brain,  but  because 
some  directing  knot  of  neurones  is  necessary  here  as  elsewhere.  Appar- 
ently all  the  centers,  nerve-paths,  and  muscles  concerned  in  speaking, 
writing,  drawing,  or  otherwise  representing  ideas  as  concepts  constitute 
the  special  physical  basis  of  cognition.  (See  the  discussion  of  speech  in 
the  latter  part  of  the  chapter  on  the  Muscles,  page  394.) 

Jennings'  work  on  the  mental  process  of  infusoria  is  of  fundamental 
value  in  the  theory  of  the  relation  of  body  and  mind. 

Memory  is  the  faculty  l)y  which  organisms  retain  their  experiences. 
As  we  have  already  noted,  it  is  the  basis  on  which  habits  are  formed,  and 
in  general  terms  mental  and  bodily  processes  are  inconceivable  without 
it.  Corresponding  with  memory  must  be  traces  of  some  sort  in  the 
body-protoplasm,  but  of  the  nature  of  these  records  no  one  as  yet  has 
the  slightest  notion.  We  know  only  certain  of  the  laws  which  appear  to 
underlie  the  function  in  the  organism. 

Almost  more  than  any  other  attribute  of  mind,  memory  is  a  natural 
gift,  and  it  varies  greatly  in  its  perfection  in  different  individuals,  A  good 
memory  is  a  true  gift  of  fortune  for  it  ordinarily  does  as  much  as  any 
other  thing  to  bring  success  in  life,  since  he  who  has  it  possesses  a  double 
and  quadruple  store  of  percepts  and  of  concepts  at  his  instant  command. 
This  is  the  more  important  because  it  appears  that  the  memory  is  little 
capable  of  true  development.  One  may  acquire  the  habit  of  trying  to 
remember  and  thus  practically  enlarge  to  some  extent  his  memorizing 
powers,  but  observation  no  less  than  actual  experiment  in  the  laboratories 
shows  that  the  grasp  and  range  of  this  recording  and  recalling  faculty 
can  be  little  developed  by  any  known  means.  We  have  to  look  espe- 
cially in  the  nervous  system  for  the  innate  difference  in  memories, 
and  it  may  be  surmised  to  have  its  basis  in  some  unknown  plasticitv 
and  tenacity  of  protoplasm  especially  of  the  neural  variety:  "wax  to 
receive  and  marble  to  retain." 

Sleep  is  another  condition  quite  as  evidently  physiological  as  psvcho- 
logical.  From  either  view-point  there  are  many  things  about  it  still 
unknown  and  the  subject  therefore  of  dispute.  Still,  much  that  is 
definite  about  its  psychophysiology  is  fairly  well  settled.  In  ancient 
times  the  mystery  of  sleep  found  expression  in  some  of  the  most  striking 
suppositions  and  superstitions  of  all  anthropology. 

The  reason  for  sleep  lies  obviously  in  the  fact  that  all  finite,  material 
things  wear  out,  and  to  continue  acting  require  renewal.  Entirelv  de- 
prived of  sleep  a  person  would  live  only  about  a  week — perhaps  not  so 
long.  A  few  organs  which  work  intermittently,  for  example  the  heart, 
rest  amply  between  actions,  but  the  majority  work  continuouslv,  as  it 
were,  for  longer  periods  and  demand  corresponding  periods  of  rest  in 
order  that  the  wear  and  tear  may  be  repaired  and  that  anabolism  may 
restock  the  tissue  with  efficient  energies.  For  this  repair  in  the  muscles 
or  in  the  glands  sleep  is  not  required,  for  these  refit  themselves  for  work 
by  simple  cessation  of  activity.     It  is  the  neural  tissues  apparentlv  that 


422  MEXTAL  FUNCTION 

demand  the  peculiar  conditions  of  sleep  for  the  recovery  of  their  co- 
ordinating energies.  ^Meanwhile,  however,  everv  portion  of  the  body 
rests  more  or  less  completely,  for  cjiiiet  in  the  nervous  system  normally 
implies  repose  in  the  other  tissues.  Did  we  know  the  nature  of  the  ner- 
vous impulse  and  of  nerve-katabolism  generally,  explanation  of  sleep 
would  probably  be  forthcoming,  or  so  far  at  least  as  its  metabolic  accom- 
paniments are  concerned. 

The  metabolism  of  the  whole  body  is  doubtless  lessened  during  sleep. 
All  researchers  into  respiration,  for  example,  find  the  oxygen-carbon- 
dioxide  exchange  decreased  (according  to  Johansson,  31  per  cent.),  and 
this  is  of  course  the  best  criterion  of  energetic  expenditure.  Most  of  this 
loss  probably  comes  from  the  greatly  decreased  action  of  the  voluntary 
muscles,  but  some  is  derived  from  the  lessening  of  activity  in  the  other 
tissues.  We  do  not  know  to  what  extent  the  accumulation  of  lactates 
(from  the  muscles  especially)  influences  the  sleep-conditions  in  the  ner- 
vous tissue.  Perhaps  it  has  nothing  to  do  with  it,  for  mental  fatigue 
easily  produces  sleep  and  the  metabolism  in  nerve  is  certainly  very  much 
less  than  that  in  muscle.  When  nervous  fatigue  is  too  great  and  verges 
on  either  acute  or  chronic  exhaustion,  sleep  sometimes  does  not  come. 
This  too  well-known  fact  would  seem  to  indicate  that  the  occasion  of 
sleep  is  a  chemical  katabolic  product  of  nervous  action  rather  than  of 
muscular  activity,  since  muscular  exhaustion  does  not  show  the  same 
abeyance  of  sleep — unless  it  be  from  muscle-pain.  But  the  truth  is  that 
the  real  immediate  occasion  ("cause")  of  sleep  is  still  unknown. 

During  sleep  the  heart  slows  its  rate  somewhat  and  the  breath-rate 
is  markedly  lessened,  deepened,  and  made  more  regular  (because 
uninterrupted  by  speech,  swallowing,  etc.).  Howell  showed  by  means 
of  the  plethysmograph  that  the  volume  of  the  hand  and  forearm 
gradually  increases  from  the  beginning  of  sleep  up  to  the  end  of  an  hour 
or  an  hour  and  three-quarters,  remains  this  size  until  about  forty-five 
minutes  before  waking,  and  then  returns  rather  quickly  to  the  normal. 
The  "general"  blood-pressure  generally  sinks  because  of  the  lessened 
heart-activity  anrl  the  dilatation  of  the  peripheral  (and  intestinal?)  capil- 
laries. It  is  likely  enough  that  this  alxlonnnal  and  peripheral  dilatation 
is  for  the  purpose  of  reducing  the  blood-supply  and  the  consequent 
metabolism  of  the  brain,  for  cerebral  anemia  is  regularly  observed  in 
sleep.  If  a  man  be  delicately  balanced  on  a  tilt-board  and  then  goes  to 
sleep,  his  head-end  rises  while  his  feet-end  descends,  and  this  tilting  is 
due  to  the  descent  of  blood  from  the  head  into  the  trunk  and  extremities. 
For  the  same  reason  one  feels  drowsy  after  a  hearty  meal,  the  ))lood  then 
going  to  the  alimentary  canal. 

The  jnipils  of  the  eyes  are  contracted  during  sleep,  and  their  smallness 
is  to  some  extent  an  index  of  the  depth  of  the  sleep.  This  action  is 
apparently  due  to  some  central  irritation;  other  sphincters  {e.g.,  of  the 
anus  and  the  bladder)  are  usefully  tightened  in  a  similar  way.  This 
tonic  contraction  is  more  or  less  inhibited  by  afferent  sensory  impulses. 
Like  the  other  voluntary  muscles,  those  moving  the  eyes  are  relaxed 


MEXTAL  FUNCTION 


423 


during  sleep,  witli  the  result  that  the  eyeballs  turn  somewhat  inward  and 
a  good  tleal  u{)ward.  General  complete  relaxation  of  the  voluntary 
muscles  on  retiring  is  an  important  habit  to  acquire,  for  only  so  are  they 
free  of  tonus,  and  this,  as  we  have  seen,  is  a  condition  of  partial  activity. 
The  unique  position  taken  by  the  cadaver  while  lying  flat  is  the  type  and 
limit  of  this  sort  of  muscular  relaxation. 

Sleep  varies  not  a  little  in  its  soundness  at  different  times  during  the 
night.  It  has  been  found  (by  comparing  the  intensities  of  sounds  neces- 
sary to  awaken  the  sleeper)  that  the  depth  of  sleep  slowly  increases  (Mon- 
ninghoff  and  Piesbergen)  for  1.25  hours,  then  deepens  very  rapidly  (see 
curve,  Fig.  243)  for  half-an-hour,  and  becomes  speedily  lighter  during 
the  next  half-hour.  From  this  time  on  until  the  middle  of  the  fifth  hour 
sleep  very  gradually  becomes  lighter,  deepens  slightly  for  another  hour, 
and  then  becomes  slowly  but  progressively  less  deep  until  awakening 
occurs.     Thus  a  person  retiring  at  ten  o'clock  is  most  profoundly  asleep 

Fig.  243 


Graphic  representation  of  the  varying  depth  of  a  natural  sleep  lasting  about  six  hours. 
Light  for  1.25  hours,  it  rapidly  deepens  during  the  next  0.5  hour;  becomes  as  rapidly  lighter 
for  the  next  0.5  hour;  then  more  slowly  for  2.25  hours;  deepens  slightly  for  1  hour  more;  then 
becomes  .slowly  lighter  until  .«ome  slight  stimulus  is  enough  to  recall  the  person  to  the  waking 
consciousness.      (Altered  from  Piesbergen.) 


at  quarter  before  twelve,  and  after  the  second  hour  the  sleep  is  compara- 
tively light  and  easily  disturbable.  Children  sleep  the  most  soundly, 
but  men  more  soundly  than  women. 

The  mental  relations  of  sleep  are  difficult  to  describe  with  certainty. 
We  think  of  sleep-consciousness  as  continuous  but  as  lowered  in  intensity 
and,  which  is  more  important,  as  separated  in  some  manner  from  the 
waking-consciousness.  In  abnormal  cases  one  waking  consciousness  is 
similarly  shut  off  by  forgetfulness  from  another,  this  amnesia  giving  us 
the  phenomena  we  call  double  or  multiple  personality.  Aside  from 
dreams  so  vivid  probably  as  to  partially  awaken  us,  we  do  not  remember 
the  mental  events  experienced  in  sleep.  Yet  there  is  excellent  and  wide- 
spread evidence  that  consciousness  persists  continually,  for  the  more 
suddenly  a  person  is  awakened  the  more  certain  he  is  to  find  himself 
in  the  midst  of  conscious  experiences  of  some  sort.  This  is  not  to  be 
accounted  for  on  any  supposition  other  than  that  consciousness  persists 


424  MEXTAL  FUXCTIOX 

at  least  until  death.  On  this  principle,  demanded  by  the  continual 
advancement  of  knowledge  about  the  relations  of  body  and  mind  and 
the  nature  of  sul^consciousness,  coma  might  give  a  subconsciousness 
down  to  its  vanishing-point,  perhaps,  in  death.  In  this  state,  however, 
the  conditions  are  different  and  abnormal,  the  essence  of  the  state  being 
one  of  depression  quite  unlike  the  partial  rest  of  sleep. 

Dreaming  and  its  congeners  somnambulism,  etc.,  probably  represent 
the  activity  of  certain  more  or  less  localized  parts  of  the  nervous  system 
separately.  One  could  almost  suppose  they  might  depend  on  the  vaga- 
ries of  the  cerebral  vaso-motion.  The  dream  is  an  unusually  vivid  experi- 
ence out  of  the  subdued  sleep-consciousness  and,  however  long  a  time 
its  content  may  represent,  lasts  only  a  very  short  time.  On  the  vaso- 
motor supposition  it  would  be  represented  by  a  temporary  dilatation  of 
some  little  region  of  the  brain-capillaries,  this  congestion  setting  up  for 
a  moment  a  more  active  metabolism  and  function.  Similar  in  origin 
may  be  the  delirium  so  common  when  the  vaso-motor  centers  are  apt  to 
be  deranged,  as  in  high  degrees  of  fever.  This  notion  as  to  the  relation 
of  dreaming  to  local  cerebral  vaso-dilatation  has  never  been  demonstrated 
and  stands  as  an  hypothesis  allowable  only  where  facts,  except  as  to  the 
actual  existence  of  cerebral  vaso-motion,  are  lacking. 

It  is  a  common  experience  that  dreams  are  more  or  less  dependent  on 
sensory  stimuli.  Thus,  a  child  from  whom  the  bed-clothes  had  fallen 
dreamed  of  a  frolic  in  a  cold  snowstorm,  and  an  over-burdened  stomach 
readily  transfers  its  load  to  the  oppressive  weight  of  a  night-mare.  Strains 
or  pressure  on  the  nerves  of  the  arm  may  readily  give  rise  to  indescribable 
impressions  of  being  overwhelmed  by  boundless  waves  of  indefinite 
matter.  Such  an  experience  forms,  moreover,  a  striking  example  of  the 
widespread  and  absorbing  mental  impression  which  may  come  from  the 
stimulation  of  a  single  nerve-trunk.  A  common  characteristic  of  the 
dream-experience  is  its  freedom  from  the  restraints  of  common  sense  and 
fact,  not  less  than  from  other  sorts  of  law:  "In  sleep  a  king,  in  waking, 
no  such  matter."  As  men  grow  old  they  dream  less  and  less,  while 
women  maintain  their  early  frequency  in  this  respect  and  dream  at  all 
life-periods  more  than  do  men  (Heerwagen).  According  to  Jastrow  it 
is  "the  vividness  of  the  emotional  background  elaborated  by  the  imagina- 
tion that  furnishes  the  predominant  characteristic  and  tendency  to 
dreams."  It  is  betv/een  the  ages  of  twenty  and  twenty-five  that  dreams 
are  vividest,  while  in  childhood  they  are  by  far  the  most  numerous. 

Despite  the  evil  dreams  that  come  at  times,  sleep  makes  up  much  of 
the  happiness  of  life,  just  as  it  constitutes  about  one-third  its  duration. 
Very  few  persons  can  work  or  feel  well  on  less  sleep  than  seven  hours 
daily,  althf^ugh  six  suffice  some;  rarely,  after  childhootl  is  passed,  does 
one  need  over  eight  hours  of  rest.  Sleep  is  indeed  to  the  world's 
multitude 

".      .      .     the  certain  knot  of  peace, 
'J'lie  Ijaiting-place  of  wit,  the  lialm  of  woe, 
The  poor  man's  wealth,  the  prisoner's  release, 
Th'  iiidiffcTciit  jiidfie  between  the  hi<rh  and  low." 


MENTAL  FUXCTJOX  425 

It  is  unfortunate  that  so  relatively  little  yet  is  known  about  its 
psychical  status  as  well  as  about  its  physical  basis.  Plspecially  does 
science  need  to  know  the  nature  of  the  break  in  memory  between  the 
sleep-consciousness  and  that  of  wakin^;  hours. 

Hallucinations,  Illusions,  and  Delusions, — These  three  sorts  of  mental 
experiences  are,  strictly  speaking,  more  or  less  abnormal,  but  they  are  of 
such  fundamental  importance  in  the  theory  of  insanity  and  so  instructive 
physiologically  that  we  may  describe  them  briefly  here.  It  is,  however, 
only  the  exceptional  "normal"  man  (and  normality  is  a  very  indefinite 
sort  of  thing)  who  does  not  often  experience  in  some  degree,  usually  as  a 
victim,  various  illusions  and  delusions.  Furthermore,  about  one-tenth 
of  the  public  have  some  time  or  other,  if  only  for  a  few  seconds,  been 
mider  the  strange  spell  of  a  true  hallucination.  (See  the  "Census  of 
Hallucinations"  made  by  H.  Sidgwick.) 

An  hallucination  is  a  percept  without  objective  occasion  or  representa- 
tion, while  an  illusion  is  a  wrongly  interpreted  percept.  A  delusion,  on 
the  other  hand,  is  of  a  conceptual  rather  than  perceptual  nature,  and  is 
a  system  of  notions  and  beliefs  contrary  to  the  facts. 

It  is  plain  from  these  definitions  that  hallucinations  and  illusions  are 
of  the  same  general  nature  and  they  probably  have  the  same  neural  basis. 
In  normal  perception  the  stimulus  comes  in  through  a  sense-organ  and 
goes  on  into  the  perceptual  brain-centers,  each  percept  employing  doubt- 
less very  many  neural  paths.  In  normal  imagination  these  same  brain- 
centers  are  doubtless  employed,  but  whether  the  sense-organs  and  the 
afferent  paths  also  are  we  do  not  know.  \Mien  an  hallucination  occurs 
these  perceptual  centers  are  stimulated  in  the  same  way  or  to  the  same 
degree  as  when  a  percept  is  formed,  and  not  in  the  manner  of  the  imagina- 
tion, and  no  one  ever  mistakes  the  product  of  imagination  for  that  of 
perception.  How  it  is  that  these  centers  are  stimulated  so  as  to  give 
the  same  sort  of  experience  as  in  perception,  no  one  as  yet  knows.  It  is  a 
process  of  imagination  changed  to  the  vividness,  objectivity,  and  reality 
of  actual  perception.  Sometimes  the  individual  is  deceived  into  sup- 
posing the  hallucination  a  true  perception,  but  more  often,  owing  to 
contradiction  between  the  hallucination  and  perceptions,  the  false 
"object"  is  realized  to  be  fallacious. 

In  illusion  there  is  some  sort  of  objective  occasion  or  stimulus,  and  the 
afferent  neural  apparatus  (end-organ  and  nerve)  employed  is  the  same 
as  in  perception.  The  result  given  to  the  brain  is  wrongly  interpreted 
by  that  organ,  so  that  the  person  perceives  differently  from  the  objective 
reality.  For  example,  if  in  looking  at  the  short  curved  lines  of  dried 
bacilli  on  a  microscope-slide  one  sees  them  bend  and  infers  therefore 
that  they  are  alive,  he  is  the  victim  of  illusion,  and  illusions  are  easy  and 
very  common  in  microscopy.  A  white  stump  in  a  swamp  at  midnight  is 
much  more  apt  to  seem  a  ghost  than  as  a  portion  of  a  dead  tree.  These 
are  illusions  and  obviously  differ  from  hallucinations  in  being  wrongly 
interpreted  perceptions;  in  hallucinations  the  latter  are  wholly  absent. 
The  physical  basis  of  both  of  these  experiences  is  evidently  much  like 


426  •  MENTAL  FUNCTION 

that  of  dreams.  Hallucinations  are  about  half  as  frequent  again  in 
women  as  in  men,  and  more  common  in  Brazilian  women,  for  example^ 
than  in  Eno'lish  women. 

Delusions  exist  wherever  knowledge  about  the  relations  of  things  is 
deficient,  mistaken,  or  deranged.  Thus,  one  thinks  of  Eddyism  as  a 
delusion  which  for  obvious  reasons  has  had  a  certain  popularity.  The 
delusions'  names,  like  their  natures,  in  the  history  of  civilization  have  been 
legion,  but  with  the  advancement  of  learning  they  continually  become 
fewer  and  "less  dangerous.  In  the  individual  delusions  are  of  all  sorts, 
all  degrees,  and  all  importances.  Some  of  the  dearest  beliefs  the  world 
knows  are  delusions:  surely  Santa  Claus  is  the  precious  birth-right  of 
every  child. 

It  is  with  the  delusions  at  the  basis  of  paranoia  (monomania),  paresis, 
etc.,  that  mental  and  legal  medicine  are  most  often  concerned.  Some- 
times these  are  based  on  hallucinations  or  on  illusions.  Whatever  their 
source  (and  we  have  no  idea  of  it  in  pathological  terms),  the  delusions  of 
an  alienated  mind  often  make  him,  long  before  he  is  put  in  a  hospital, 
one  of  the  most  dangerous  of  beings,  so  cunning  and  so  cruel  are  the 
purposes  of  such  unfortunates  apt  to  be  under  the  unnatural  stimuli  of 
these  delusions.  These  are  unknown  derangements  in  the  powers  of  the 
reasoning  aspects  of  the  mental  process. 

Anesthesia. — This  term  commonly  means  not  only  the  absence  of 
"feeling,"  as  the  word  itself  implies,  but  also  the  absence  of  pain,  anal- 
gesia. In  the  use  of  laughing-gas  (nitrous  oxide),  for  example,  pain  may 
be  lost  and  feeling  retained,  and  this  is  the  case  also  in  the  lightest  degrees 
of  the  effects  of  ether-  and  of  chloroform-inhalation.  Analgesia  and 
anesthesia  may  be  either  general  or  local.  In  the  former  case  the  anes- 
thetic is  inhaled  and,  entering  the  circulating  blood  through  the  alveolar 
walls,  is  taken  quickly  to  every  part  of  the  body.  It  is  its  action  on  the 
nervous  system  especially  which  causes  the  disturbance,  shutting  off, 
or  "loss"  of  consciousness.  Local  anesthetics  seem  to  act  by  cutting 
off  the  else  painful  impressions  passing  inward  on  the  afferent  nerves. 
We  are  concerned  now  only  with  general  anesthesia,  and  then  only  so 
far  as  consciousness  is  concerned. 

General  anesthetics  in  one  way  or  another  (just  how  is  not  yet  certain) 
check  the  conductivity  in  the  neural  tissue  and  thus  prevent  that  unifica- 
tion of  numberless  impressions  which  we  call  the  mental  process  or  con- 
sciousness. People  widely  vary  in  their  mode  of  reaction  to  anesthetics, 
but  very  often  (aside  from  the  feelings  of  suffocation,  etc.,  incident  to 
taking  the  drug)  there  is  experienced  a  vast  hurrying  of  some  great  mass 
that  is  very  variously  described.  Most  often,  perhaps,  this  mass  very 
early  begins  to  rotate,  sometimes  around  the  anesthetized  subject, 
sometimes  with  the  latter  on  its  edge,  or  within  it.  Then  the  speed 
rapidly  increases  until  the  mind  is  in  a  vortex  of  tremendous  energy  but 
without  any  suggestions  (usually)  of  terror  or  unpleasantness.  No 
limit  of  time  can  be  set  by  the  subject  to  these  long-remembered  im- 
pressions, but  often  they  seem  to  continue  throughout  the  anesthesia. 


MEXTAL  FUNCTION  ^         427 

In  reality  it  is  rather  the  memory  of  their  presence  and  nature  which 
fades  as  the  effect  of  the  anesthetic  deepens  into  the  deep  subconscious- 
ness of  surgical  anesthesia.  Doul)tless  these  two  ("unconsciousness" 
and  entire  loss  of  memory  of  consciousness)  are  the  same  so  far  as  the 
future  recall  of  the  experience  is  concerned.  The  reports  of  anesthesias 
strengthen  the  presumption  long  ago  made  that  it  is  the  break  in  memory 
which  is  the  critical  phenomenon  of  all  conditions  commonly  called 
unconscious  rather  than  that  any  condition  of  real  "unconsciousness" 
can  exist  during  "life."^ 

The  physical  basis  of  the  action  of  anesthetics  is  still  obscure.  Lately 
it  has  been  suggested,  however,  that  the  general  anesthetics  are  substances 
which  dissolve  fats,  and  the  fatty  substances  cholesterin,  lecithin,  etc., 
are  probably  constituents  of  every  cell-wall.  Perhaps  the  circulating 
ether  or  chloroform  dissolves  some  of  these  complex  substances  out  of 
the  guarding  envelope  of  nerve-cells  and  nerve-fibers,  and  thus  by  dis- 
turbing its  osmotic  interchange  alters  their  metabolism  enough  to  destroy 
their  conductivity  and  so  the  fusing  unification  on  which  attentive  con- 
sciousness in  some  way  depends. 

For  the  bodily  changes  made  by  general  anesthetics  the  reader  is 
referred  to  treatises  on  general  and  dental  surgery. 

'  Accounts  of  experiences  during  general  anesthesia  are  sought  by  the  author, 
and  questionaire-blanks  for  this  purpose  will  be  promptly  mailed  on  application 
to  him. 


CHAPTER    XIII. 

REPRODUCTION  AND  DEVELOPMENT. 

The  eternal  changefulness  of  things  is  impressively  typified  in  the 
rapid  succession  of  generations  consequent  on  man's  inherent  mortality. 
It  is  this  which  makes  reproduction  one  of  the  three  or  four  universally 
essential  functions  of  all  organisms,  for  individuals  die  and  must  be 
replaced  if  the  races  are  to  persist.  The  means  by  which  this  replace- 
ment is  brought  about  constitute  one  of  the  most  elaborate  of  all  psycho- 
physical mechanisms,  while  the  record  of  the  process  of  the  individual's 
growth  to  maturity  and  his  subsequent  decadence  are  the  history  of  life 
and  death,  are  physiology  itself.  To  these  two  important  subjects, 
reproduction  and  development,  so  interwrought  with  life's  happiness  and 
misery,  so  vastly  complex  in  all  their  details,  we  can  here  pay  but  inade- 
quate attention  and  give  but  insufficient  space.  We  can  discuss  briefly 
the  bare  outlines  of  only  the  somatic  process,  in  part  the  physiology  of 
the  organs  concerned,  but  must  leave  undescribed  entirely  all  that  great 
mass  of  psychological,  social,  anthropological,  and  criminological  facts 
which  from  any  adequately  broad  view-point  constitute  part  of  the  deep 
problems  of  sex  and  of  racial  progress— basal  truths  in  human  physiology 
considered  as  the  science  of  man's  normal  living.  Even  medical  men, 
the  proper  teachers  of  mankind,  because  of  the  hereditary  prudery  of 
the  race  still  reserve  from  common  knowledge  reproductive  facts  and 
theory  which  would  be  of  immense  value  to  mankind,  making  happy  the 
lives  of  multitudes  of  boys  and  girls  which  without  this  needful  informa- 
tion will  be  stained  with  unnecessary  disease  and  misery. 

It  is  inevitable  that  with  so  large  a  number  of  dissimilar  animal  forms 
as  there  are  (a  million  or  so),  there  should  be  many  processes  of  genera- 
tion. All  the  forms  of  reproduction  may  be  classed,  however,  either  as 
asexual  or  sexual  except  in  the  one-celled  animals,  the  protozoa,  in 
which  we  find  budding,  simple  division,  spore-formation,  and  one  or  two 
other  more  or  less  similar  processes.  The  asexual  process  in  multicells 
is  seen  chiefly  as  budding  in  some  form  or  other.  The  sexual  process 
proper  involves  the  union  of  special  reproductive  cells  which  have  small 
part  in  the  general  functions  of  the  body,  and  largely  serve  this  function 
of  reproduction.  The  special  germ-c-ells  coming  from  one  (the  male) 
sex  are  termed  spermatozoa,  tiiosc  from  the  other  (female)  sex  ova,  and 
usually  their  combination  in  fertilization  is  necessary  for  the  origination 
of  a  new  individual.  Jii  a  few  cases,  however,  the  female  cells  (ova) 
develop  into  infertile  animals  parthenogcnically,  tliat  is  without  being 
fertilized  by  male  protoplasm.     In  sexual  reproduction  the  ovum  stands 


PUBERTY   AXD  MENSTRUATION  429 

for  body-material  and  for  relative  passivity,  while  the  spermatozoon  is 
the  supplier  of  tlie  activity  and  the  energy  by  which  alone  the  body- 
matter  becomes  spontaneously  motile  and,  in  short,  alive.  Both  aspects 
of  the  actual  animal  are  essential,  a  material  body  and  the  activity 
whereby  that  organized  material  may  adjust  itself  to  its  environment. 

The  cellular  reproduction  of  man,  as  of  all  other  mammals,  takes  place 
by  mitosis  (karvokinesis),  as  distinguished  from  the  amitosis  or  direct 
cell-division  of  many  protozoans  and  some  metazoans.  An  outline 
of  the  mitotic  process  w^as  given  in  the  chapter  on  Protoplasm  (see 
page  45). 

PUBERTY  AND  MENSTRUATION. 

Our  first  inquiry  must  be  as  to  how  the  reproductive  apparatus  is 
made  ready  for  use  in  the  developing  adolescent,  especially  in  the  girl,  as 
a  preliminary  to  a  description  of  that  use — the  fertilization  of  the  woman 
by  the  man.  Here,  as  in  the  other  functions,  a  detailed  knowledge  of  the 
genital  apparatus  of  each  sex,  to  be  obtained  from  anatomy,  is  presup- 
posed. 

Puberty  in  the  Male. — From  the  beginning  of  voluntary  control  during 
the  latter  part  of  the  first  half-year  of  extra-uterine  life  the  boy-baby 
shows  in  some  slight  respects  his  functional  difference  from  the  girl- 
baby — he  has  especially  more  tendency  to  the  initiative  and  is  on  the 
average  bolder  in  his  activities.  None  the  less,  up  to  the  age  of  twelve 
or  fourteen  the  nature  of  the  boy  is  like  that  of  the  girl  in  a  much  greater 
degree  than  ever  again  it  can  normally  be.  Many  perfectly  normal  girls 
up  to  this  age  and  sometimes  beyond  it  do  boyish  things,  and  vice  versa. 
It  must  be  deemed  physiologically  a  distinct  advantage  to  both  sexes 
that  the  boys  and  girls  should  mingle  freely  and  naturally  up  to  the  age 
of  twelve  and  freely  also,  if  not  quite  naturally,  beyond  that  time.  Such 
association  keeps  the  boy  from  becoming,  sometimes,  a  "boor,"  and  the 
girl  from  becoming  a  prude. 

When  about  fourteen  or  sixteen  years  of  age,  in  temperate  climates, 
the  boy's  organism  begins  to  change  and  with  it  his  mental  nature  more 
or  less,  although  to  a  much  smaller  degree  perhaps  than  in  case  of  the  girl. 
The  testicles  rapidly  increase  in  size  and  become  more  pendulous  and 
the  dartos  tunic  more  contractile.  The  penis  grows  in  length  and  soon 
develops  in  its  cavernous  bodies  an  increased  power  of  erecting,  while 
the  prepuce  becomes  more  easily  removable  over  the  glans.  The  vocal 
cords  develop  and  elongate  especially,  and  during  these  changes  are  apt 
to  be  badly  controlled  in  speaking.  The  shoulders  broaden  and  hair 
grows  on  the  lower  part  of  the  face,  in  the  axilla,  and  on  the  lowest  middle 
part  of  the  abdomen,  over  and  around  the  penis.  The  moral  sentiments 
become  more  conspicuous  in  the  nature  of  the  boy,  and  beauty  especially 
becomes  for  the  first  time  a  reality  to  him.  Around  his  whole  being 
floats  a  consciousness  of  new  powers,  new  interests,  and  new  life,  for 
this  sexual  flood-tide  pervades  without  his  realizing  it  perhaps  every 


430 


REPRODUCTIOX  AXD  DEVELOPMENT 


portion  of  his  two-faced  mental  and  physical  nature.  In  some  respects 
this  is  the  climax  of  the  delight  of  mortal  experience,  this  opening  of 
the  world's  real  life  to  the  childish  mind.  By  a  study  of  the  phenomena 
of  puberty  including  the  far-reaching  bodily  changes  not  less  than  the 
all-pervading  alterations  in  the  mental  process,  one  learns  to  appreciate 
how  completely  intermixed  is  sexuality  in  most  of  the  affairs  of  life.  Its 
instinctive  influence  surpasses  that  of  all  other  functions  save  nutrition, 
and  these  two  accord  in  being  irrepressible. 


Fig.  24-i 


p.n.\Lji 


.The  female  reproductive  organs,  to  show  their  nerve-sujiply :  p.n.,  phrenic  nerve;  a.n.,  splanch- 
nic; l.g.a.,  lumbar  ganglion  (sympathetic);  g.u.p.,  great  uterine  plexus;  r.h.p.,  right  hypogastric 
plexus;  8.p.,  sacral  plexus;  r.c.g.,  right  cervical  gangli6n;  ii.n.,  vagus;  e.g.,  solar  ganglion;  s.r.g., 
suprarenal  ganglion;  i.r.(/.,  infrarenal  ganglion;  s.  and  i.g.,  superior  and  inferior  genital  ganglia; 
ape.p.,  spermatic  plexus  (ovarian  nerves).      (Frankenhiiuser  via  Edgar.) 

Puberty  in  the  Female. — More  profound  by  far  than  the  changes  that 
constitute  puberty  in  the  boy  are  those  which  make  of  the  maiden  child 
a  woman.  The  average  young  girl  while  a  child  is  more  like  a  boy  than 
the  average  boy  is  like  a  girl — that  is  to  say,  the  pubertal  changes  of  the 
female  are  more  revolutionary  than  are  those  in  the  male. 

They  come  about  somewhat  more  gra(kially,  and  soon  after  the  age 
of  twelve  in  temperate  climates  (sometimes  as  early  as  nine  in  the  tropics) 
the  proper  sexual  changes  begin.     As  one  may  read  in  Aristotle,  men- 


PUBERTY  AXD  MEXSTRUATION 


431 


struation  l)egins  when  the  breasts  are  two  fingers'  breaflth  high.  The 
whole  body  takes  part  in  this  evolution,  which  fits  the  individual  to  bear 
children.  The  specific  gravity  of  the  blood  rises  and  the  pulse-rate 
accelerates,  although  somewhat  less  than  in  boys.  The  chest  enlarges, 
but  so  much  does  the  pelvis  grow,  especially  laterally,  that  the  hips 
become  very  much  more  prominent  in  comparison  with  the  shoulders. 
Deposits  of  fat  about  the  limbs  and  between  the  muscles  cause  all  contours 
to  become  more  rounded.  The  face  changes  in  a  marked  degree  and  in 
some  indescribable  manner  becomes  the  face  of  a  woman.  The  larynx 
enlarges  and  the  voice  nearly  doubles  its  range.  The  breasts  develop 
their  adult  rotunditv,  as  does  also  the  abdomen.     The  sexual  organs 


A  virgin  uterus  (twenty-two  years). 

A,  from  in  front  and  below:  1,  body;  2,  angles;  3,  cervix;  4,  opposite  the  os  internum;  5, 
vaginal  part  of  the  cervix;   6.  os  externum;   7,  vagina  (distended). 

B,  sagittal  section:  1,  anterior  face;  2,  utero-vesical  cul-de-sac;  3,  posterior  face;  4,  body; 
5,  cervix;  6,  isthmus;  7,  body-cavity;  8,  cervix-cavity;  9,  os  internum;  10,  os  extemum's 
anterior  lip;    11,  os  externuni's  posterior  lip;    12,  vagina. 

C,  transverse  longitudinal  section:  1,  body-cavity;  2,  lateral  wall;  3,  upper  wall;  4,  horn; 
S,  os  internum;   6,  cervix-cavity;   7,  arbor  vitaj  cervicis;   8,  os  externum;   9,  vagina.      (Sappey.) 

proper,  especially  the  uterus,  develop  in  size  and  shape,  each  of  them 
changing  in  many  particulars  into  the  condition  of  greatest  fitness  for 
its  particular  part  in  the  momentous  process  of  procreation.  All  the 
glands  concerned  markedly  develop  and  play  no  small  part  in  the  new 
experiences  of  the  new  woman;  the  vascularity  especially  of  all  portions 
of  the  genital  system  increases  greatly.  Hair  grows  on  the  mons  veneris, 
etc.,  and  in  the  axilla?. 

The  mental  changes  of  the  commencement  of  womanhood  we  may 
not  attempt  to  describe.  They  are  homologous  to  those  occurring  in 
the  male,  and  all  have  their  physiological  meaning  and  explanation  in 
the  new  tendencies  toward  and  fitness  for  fertilization  and  the  bearincf  of 


432  REPRODVCTIOX  AXD  DEVELOPMEXT 

children.  It  is  from  this,  biologically  speaking,  that  these  new  desires 
and  thoughts  and  emotions  get  their  sweetness  and  their  worth,  as 
indeed  the  normal  woman  finally  learns  to  realize. 

Of  all  the  new  activity  m  the  female  organs  the  two  new  functions  of 
ovulation  and  menstruation  are  in  a  way  probably  the  most  essential, 
the  former  in  particular.  It  is  not  yet  known  how  these  are  related 
biologically,  hence  we  describe  them  separately  as  two  processes  rather 
than  as  parts  of  one. 

Ovulation  is  the  process  in  which  a  matured  ovum  breaks  out  of  the 
ovary  and  is  started  down  the  Fallopian  tube  toward  the  uterus.  Every 
lunar  month  at  least  one  of  the  Graafian  follicles  makes  its  way  to  the 
surface  of  the  ovary,  but  just  how  this  passage  through  the  stroma  occurs 
and  is  controlled  is  not  understood.  ^Mien  it  arrives  there  and  projects 
beyond  the  general  surface  of  the  ovary,  the  outer  walls  of  the  follicle 
may  degenerate  and  give  way,  thus  freeing  the  ovum  and  the  plasma 

Fig.  246 


A  .sectional  view  of  the  left  Fallopian  tube,  showing  its  numerous  channels,  its  widely 
spreading  openings,  and  its  close  connection  with  the  ovary.      (Sappey.) 

about  it  in  the  follicle  on  the  ovarian  surface.  The  follicle's  rupture 
may  come  from  its  over-distention  with  lymph,  from  excessive  congestion 
of  the  ovarian  stroma,  or  from  the  reflex  active  contraction  of  the  ovarian 
musculature  in  the  excitement  of  coitus.  The  last-mentioned  possi- 
bility has  been  usually  overlooked.  The  inner  lining  of  the  Fallopian 
tubes,  including  the  trumpet-shaped  fimbrise,  is  ciliated,  and  the  cilia  all 
wave  so  as  to  cause  a  slight  but  continuous  stream  of  lymph  down  the 
tubes  toward  the  womb.  If  the  fimbriated  end  of  the  tube  embraces  the 
side  of  the  ovary  during  ovulation,  it  is  easy  to  see  that  the  minute  ovum 
(0.2  mm.  in  diaTiicterj  would  very  j)robal)ly  l)e  drawn  into  the  wide 
openings  of  the  tube  and,  once  started,  be  passed  slowly  along  one  of  the 
very  narrow  channels  into  the  uterus.  The  rate  of  this  passage  averages 
perhaps  20  mm.  per  day.  In  trying  io  define  how  this  functional  con- 
nection between  ovary  and  tube  can  take  place  so  regularly  (abdominal 
pregnancies  are  relatively  uncommon  though  by  no  means  rare),  it  must 
be  kept  in  mind  tiuit  there  are  no  open  spaces  in  the  abdominal  cavity, 


PUBERTY   AXD   MEXSTRUATION 


433 


for  the  viscera  fit  snn^'ly  to(i;ether,  and  that  the  few  spaces  there  are 
between  them  are  filled  witii  lymph.  The  plasma  poured  out  with  the 
ovum  serves  undoubtedly  to  float  the  latter  into  the  stream  trending  into 
the  tube,  for  else  the  peculiar  nature  of  the  follicle  is  unintelligible. 
There  is  however,  also  a  permanent  anatomical  connection  between  the 
tube  and  the  ovary  by  means  of  the  ovarian  fimbria,  and  it  is  likely  that 
it  is  by  this  channel  that  the  ova  usually  pass,  the  other  fimbriae  being 
present  perhaps  to  pick  up  the  stragglers  from  this  straight  and  narrow 
way.  Sometimes  the  ovum  becomes  fertilized  on  or  near  the  ovary  and 
fails  to  reach  the  safe  channel  of  the  tube,  the  fetus  then  developing  as  an 
abdominal  (ectopic)  pregnancy.  Maturation  occurs  either  just  before 
or  just  after  the  follicle's  rupture,  and  fertilization,  while  occurring, 
usually  in  the  peripheral  part  of  the  tube,  may  take  place  at  any  time 
after  the  rupture,  even  in  the  uterus.  The  relations  of  the  two  ovaries 
as  regards  ovulation  are  unknown,  but  there  is  a  likelihood  that  both 
ovaries  ovulate  everv  month. 


Fig.  247 


Section  through  the  Fallopian  tuba.      (Bates.) 

The  Corpus  Luteum. — ^Mien  the  follicle  has  burst  and  freed  its  ovum 
its  duties  as  a  follicle  are  done.  If  we  may  trust,  however,  the  recent 
work  of  several  men,  and  especially  of  Frankel,  the  follicle  forthwith 
takes  on  a  new  function,  that  of  producing  an  internal  secretion,  which 
stimulates  the  growth  of  the  muscular  parts  of  the  sexual  organs,  and 
perhaps  of  others  (heart,  for  example?),  to  meet  the  demands  of  the 
expected  pregnancy.  Aside  from  the  experimental  evidence  for  this,  the 
hollo^\aiess  and  the  large  size  of  the  Graafian  follicle  in  themselves  are 
additional  testimony.  These  conditions  apparently  are  not  necessary 
merely  for  the  development  of  (and  maturation  of?)  the  ovum  but  rather 
preparation  for  the  corpus  luteum.  This  glandular  (?)  organ  is  formed 
according  to  von  Baer  substantially  as  follows :  When  the  follicle  bursts 
open  in  ovulation  to  allow  of  the  ovum's  release,  blood  escapes  into 
28 


434 


REPRODUCTIOX  AXD  DEVELOPMENT 


the  drained  cavity  of  the  foUicle,  whose  walls,  especially  the  stratum 
granulosum,  remain.  These  latter  cells  degenerate  and  the  internal 
layer  beneath  them  by  proliferation  soon  gives  rise  to  a  cellular  mass 
sufficient  to  fill  the  now  restored  sphere  of  the  follicle.  Trabeculse  of 
fibrous  tissue,  containing  an  abundance  of  blood-vessels,  soon  divide 
the  little  body  into  lobules.  The  cells  composing  this  new  mass  are 
colored  yellow  by  lutein,  a  lipochrome  of  unknown  composition  which 
gives  the  blood-serum  its  faint  yellowness. 

In  case  the  liberated  ovum  be  not  fertilized,  in  about  three  weeks  the 
yellow  cells  become  more  and  more  white  like  connective-tissue  of  a 
special  cicatricial  sort,  and  in  course  of  time,  this,  now  called  the  corpus 
albicans,  almost  disappears.  If  we  suppose,  as  many  at  present  do,  that 
o\Tjlation  takes  place  normally  about  a  fortnight  before  menstruation, 


Fig.  248 


y^,^^ 


Section  in  the  ovary  of  a  cat:  1,  free  peritoneal  border  of  the  ovary;  l',  attached  border; 
2,  central  stroma,  fibrous  and  vascular  in  its  structure;  3,  peripheral  stroma  containing  unstri- 
ated  muscle-fibers;  4,  blood-vessels;  5,  Graafian  follicles  in  the  earliest  stage  (about  36,000  in 
number  altogether);  6,  7,  8,  more  advanced  and  larger  follicles  embedded  more  deeply;  9,  an 
almost  mature  follicle  containing  a  conspicuous  ovum;  9',  a  follicle  which  has  accidentally  lost 
its  ovum;    10,  a  corpus  luteum.      °/,.      (Schron.) 

it  is  clear  that  the  contents  of  the  corpus  luteum  might  well  enough  influ- 
ence the  changes,  constructive  and  tlien  destructive,  which  occur  in  the 
uterus  previous  to  the  outward  flow  of  uterine  debris.  The  sexual  appa- 
ratus is  constructed  and  acts,  however,  on  the  supposition  of  continually 
repeated  conception  and  pregnancy,  and  yet  in  the  above  manner  it  pro- 
vides for  fHsappointiiu'iit. 

If,  however,  the  ovum  be  fertilized  within  a  week  or  so  after  ovulation 
(the  ovum  will  persist  at  least  as  long  as  this),  the  corpus  luteum  vera,  as 
it  is  then  called,  becomes  more  fully  developed  and  larger.  More  than 
this,  it  persists  in  its  entirety  until  after  j)arturitif)n,  when  it  degenerates 
in  praftically  the  same  way  as  does  the  cor})iis  albicans.  On  this  hypoth- 
esis, then,  the  hollow  sphere  from  wliic-h  an  ovum  has  escaped  becomes 
forthwith  filled  with  epithelium  wliidi  ])rovides  a  stimulant  for  such 
temj)orary  devclopincnf  of  the  organism  as  is  required  for  the  growth 


PUBERTY  AXD  MENSTRUATION  435 

and  birth  of  the  new  being.  In  case  fertilization  fail,  the  stimulating 
material  ceases  to  be  produced  and  the  uterus  rids  itself  by  menstruation 
of  the  now  useless  growth  in  its  mucosa  (see  Ijelow).  Things  fit 
together  too  well  on  this  hypothesis  to  warrant  its  rejection  unless  dis- 
proved.    None  the  less,  at  present  it  is  a  theory  only. 

^^^lile  it  is  true  that  the  ovary  probably  discharges  an  ovum  each  lunar 
month,  the  exact  time-relation  between  this  event  and  menstruation  is 
still  a  matter  of  research  and  discussion,  a  discussion  which  can  be  made 
clearer  when  the  facts  and  theory  of  menstruation  have  been  given. 

Menstruation  is  the  monthly  hemorrhage  which  occurs  from  the 
uterus  in  women  and  in  some  of  the  higher  apes.  It  occurs  (})ut  not 
monthly)  in  the  females  of  many  other  species,  such  as  the  equine,  bovine, 
and  canine  animals.  It  begins  its  periodical  routine  at  puberty  (as  early 
as  the  ninth  year  in  Africa  and  as  late  as  the  seventeenth  in  Lapland), 
and  continues  normally,  except  during  the  pregnancies  and  lactations, 
until  the  menopause  at  the  forty-fifth  or  fiftieth  year.  Some  women, 
but  not  many,  menstruate  throughout  pregnancy;  very  rarely  even  fertile 
women  do  not  menstruate  at  all.  Individual  differences  as  regards 
menstruation  are  great  in  the  frequency,  the  amount  of  hemorrhage, 
the  duration,  the  ages  of  commencement  and  cessation,  the  secondary 
phenomena,  etc.  On  the  average,  however,  the  occurrences  are  as 
follows : 

At  intervals  of  twenty-eight  days  a  flow  of  blood  comes  from  the  uterus 
and  continues  for  four  or  five  days.  IMany  women  are  unwell  every  three 
weeks  and  fewer  show  an  interval  of  thirty-two  or  thirty-three  days,  these 
being  the  normal  limits.  The  more  civilized  and  "cultured"  the  woman 
the  more  pronounced  is  the  flow,  it  being  much  less  in  the  savage  races. 
Preceding  the  actual  hemorrhage  there  are  apt  to  be  many  varied  pre- 
monitory signs  of  its  approach:  indefinite  and  irregular  pains, chilliness, 
nervous  instability  and  irritability;  in  many  women  these  signs  of  a 
general  stimulation  of  the  nervous  system  are  seen  especially  about  a 
week  before  the  flow  begins.  The  breasts  are  enlarged  by  the  congestion 
and  made  firmer  and  somewhat  tender  to  the  touch.  The  amount  of 
urea  excreted  becomes  smaller.  The  bloody  discharge  begins  very  grad- 
ually and  is  apt  at  first  to  be  somewhat  watery.  In  a  day  or  so  the  flow 
becomes  established  often  with  no  little  uterine  and  ovarian  pain  (dys- 
menorrhea), continues  more  or  less  abundantly  for  one  or  two  days,  and 
then  in  one  or  two  days  more  gradually  stops.  The  quantity  of  blood 
ordinarily  ranges,  between  100  and  200  c.c,  but  is  oftep  very  scanty, 
especially  in  anemic  young  women  w^ho  have  too  little  physical  exercise. 
Often,  too,  it  is  as  much  as  400  or  500  c.c.  in  amount.  It  is  because  of 
this  hal)itual  loss  of  blood  that  women  stand  severe  accidental  hemorrhage 
better  than  do  men.  In  a  degree  the  ancient  Jewish  notion  of  the  cat- 
amenia  as  a  means  of  purification  is  physiologically  justified,  for  many 
women  are  "more  normal"  in  many  ways  just  after  menstruation  than 
before.  This  relief  doubtless  originates  reflexly  in  the  decrease  of  the 
congestion  in  the  sexual  apparatus  and  to  a  lesser  extent  in  that  of  the 


436 


REPRODUCTION  AND  DEVELOPMENT 


whole  body.  Another  possible  source  of  relief  lies  in  the  fact  that  the 
body  temperature  is  highest  a  short  time  before  menstruation.  Sexual 
desire  is  increased  over  the  average  just  before  and  also  after  the  menses, 
the  period  itself  being  the  time  of  heat  or  rut  in  the  brutes.  In  the  human 
male  also  there  appears  to  be  a  somewhat  similar  periodicity  of  desire 
dependent  doubtless  on  the  accumulation  or  else  on  the  liberation  from 
the  testicular  tubules  of  spermatozoa.  It  is  not  apparent  that  the  moon 
has  anything  to  do  with  the  periodicity  in  either  sex — the  notion  is  one 
of  the  many  from  the  superstitious  past.  The  social,  medical,  and  legal 
relations  of  menstruation  make  it  and  its  accompaniments  (such  for 
example  as  nervous  instability),  matters  of  no  small  practical  importance. 


Fig.  249 


100 


75 


50 


25 


0     .  14  15  16  17  18  19  J) 

Graphic  suggestion  of  the  fluctuations  of  the  vital  processes  as  related  to  menstruation.  The 
days  of  the  lunar  month  are  indicated  on  the  abscissa-line  C  D;  menstruation  lasting  part  of 
the  six  shaded  days,  m,  n.  The  percentages  of  intensity  of  the  life-processes  (including  pulse- 
rate,  blood-pressure,  heat-radiation,  muscular  strength,  lung-cai^acity,  strength  of  respiration, 
reacti'jn-time  of  patella  reflex)  are  indicated  numerically  along  the  ordinate-Iine  C  E,  by  the 
varying  height  of  the  curve  A  B,  in  the  ordinary  way  of  the  graphic  melhod.  Thus,  just 
before  menstruation  vitalitj'  is  at  its  height,  ready  to  be  reproduced.      (Nagel.) 


The  uterine  'phenomena  causing  the  monthly  flow  are  relatively  simple. 
The  columnar  ciliated  epithelium  of  the  uterine  body, » together  with  the 
outer  portions  of  the  mucosa  beneath  it,  degenerate  more  or  le.ss  and  are 
washed  out  of  the  uterus  and  vagina  by  the  flow  of  l>lood  from  the  capil- 
laries and  smallest  arterioles  lacerated  in  this  process.  In  some  women 
this  epithelial  degeneration  may  be  almost  or  quite  lacking.  Both  the 
uterine  glands  and  the  tissue  between  them  undergo  fatty  degeneration 
and  are  excreted,  the  layer  of  ti.ssue  given  oil"  being  fi'om  3  to  6  mm.  thick, 
and  appearing  sometimes  as  a  complete  cast  of  the  uterine  interior  walk 
The  blood  passed  into  the  vagina  because  of  its  large  admixture  with 


IMPREGNATION  437 

mucus  does  not  clot.  The  amnioniacal  odor  is  due  largely  to  needless 
decomposition  in  the  vagina.  The  normal  biological  odor  sometimes 
to  be  distinguished  about  menstruating  women  is  a  very  different  odor; 
it  conies  from  the  skin,  and  is  somewhat  aromatic  and  by  no  means 
unpleasant  (Ellis).  The  mucosa  partly  given  off  during  the  periods  is 
regenerated  in  a  week  or  less  after  the  flow  ceases. 

The  relation  of  ovulation  to  menstruation  is  still  somewhat 
uncertain;  the  most  likely  theory  has  already  been  discussed.  That 
there  is  a  relation  and  a  dependence  may  not  be  doubted,  as  we  have 
seen.  Yet  girls  sometimes  conceive  and  bear  children  before  they  have 
menstruated,  and  so  occasionally  do  women  years  after  their  menses 
have  ceased  at  the  climacteric  (menopause).  It  is  certain,  then,  that 
menstruation  is  not  essential  to  normal  conception,  while  ovulation 
obviously  is,  for  without  the  freeing  of  the  ovum  the  sperms  could  not 
gain  access  to  the  latter.  The  chief  problem  then  is  as  to  the  function 
of  the  monthly  flow.  Another  question  not  less  important,  practically 
as  well  as  theoretically,  is  the  time-relation  of  menstruation  to  ovula- 
tion, since  everywhere  the  menses  are  used  as  a  sort  of  almanac  for 
predicting  the  date  of  delivery.  These  problems  are  made  yet  more 
difficult  by  our  ignorance  of  just  what  happens  in  the  ovaries  during  the 
reflex  excitement  of  coitus.  On  Fraenkel's  hypothesis,  ovulation  should 
occur  rhythmically  once  a  month  two  weeks  before  menstruation,  the 
rhythm  depending  on  entirely  unknowii  conditions  perhaps  in  the  ovarian 
tissues.  From  this  point  of  view  coitus  would  have  little  influence  in 
rupturing  Graafian  follicles,  and  the  musculature  of  the  ovaries  fails  of  a 
known  function.  If  we  suppose,  then,  that  menstruation  is  occasioned 
by  the  degeneration  of  the  uterine  mucosa  after  being  disappointed 
in  its  expectation  of  feeding  a  fertilized  ovum,  we  shall  be  as  near  to  an 
explanation  of  the  menses  as  can  be  had  at  present. 

The  evidence  that  some  internal  secretion  of  some  part  of  the  ovary 
occasions  the  monthly  flow  is  very  conclusive,  for  removal  of  all  of  both 
ovaries  stops  menstruation  permanently,  while  if  only  a  small  part  of 
one  ovary  be  left  the  process  continues.  This  is  quite  in  line  with  the 
conditions  under  which  enzymes  in  general  work.  ^Moreover,  after 
complete  removal,  with  cessation  of  the  catamenia,  the  successful  trans- 
plantation (Glass)  into  the  abdominal  cavity  of  a  fragment  of  ovary 
again  starts  the  menstrual  rhythm.  In  the  over-radical  gynecology  of 
a  decade  ago  there  were  all  too  many  opportunities  for  testing  these  now 
well-known  facts.  Experiments  on  the  transplantation  of  corpora  lutea 
only  remain  to  be  performed. 


IMPREGNATION. 

Biologically  considered  woman  is  female  in  order  to  bear  children  and 
to  nurture  them  during  their  uniquely  long  childhood.  The  first  step 
in  this  long  and  complex  process  in  which  the  girl  becomes  a  woman  is  a 


438 


REPRODUCTION  AXD  DEVELOPMEXT 


willingness  at  least  to  be  sexually  loved, whereby  alone,  speaking  generally 
fertilization  of  her  ova  is  possible.  This  function,  coitus,  is  a  very  com- 
plex series  of  activities  differing  somewhat  in  the  two  sexes,  but  in  each 
homologous  to  that  of  the  other.  Strictly  speaking,  the  muscular  actions 
are  of  the  voluntary  sort,  but  they  tend  under  the  perfectly|normal  condi- 
tions of  sexual  vigor  to  become  practically  reflex  in  nature,  as  are  plainly 
the  secretorv  processes  and  the  emotional  accompaniments.  For  a 
detailed  description  of  these  important  events  the  reader  is  referred  to  the 
various  scientific  discussions  in  the  more  elaborate  treatises  on  physiology, 
psychology,  and  obstetrics. 

Fig.  250 


The  erectile  bodies  of  the  vulva:  1,  symphysis;  2,  pubic  bone;  3,  ischium;  4,  ischial  tuber- 
osity; 5,  vestibule,  including  tlie  mouth  of  the  urethra  and  the  vaginal  entrance;  6,  anus;  7, 
glans  of  the  clitoris;  8,  suspensory  ligament  of  the  same;  9,  dorsal  plexus  of  the  same;  10,  cor- 
pus cavernosum;  11,  Bartholin's  glands;  12,  crus  of  the  clitoris;  13,  bulbo-cavernosal  muscle. 
The  erectile  parts  are  injected,  and  the  four  labia  are  cut  away.      (Rauber.) 

Semen  is  the  term  given  to  the  complex  viscous  fluid  poured  out  by 
the  male  during  the  orgasm.  It  has  long  been  known  that  the  sperma- 
tozoa are  its  only  essential  elements,  the  other  parts  being  but  physical 
and  chemical  menstrua  for  the  conveyance  and  continued  vitality  of  these 
sperms.  Each  cui^ic  centimeter  of  semen  contains  al)out  fifty  millions 
of  these  male  cells.  This  substance  is  an  opaque,  whitish,  streaky 
fluid  with  a  quite  characteristic  odor,  and  wholly  insoluble  in  water. 
Chemically  it  contains  nuclein,  the  base  protamine,  proteids,  lecithin, 
cholesterin,  inorganic  salts,  and  fat  (IMiescher).  Crystals  found  in  dried 
semen  are  supposed  by  some  to  be  a  phosj)iiate  of  a  base  called  spermin, 
and  to  cause  the  odor  of  semen.  Camus  and  Gley  found  an  enzyme 
in  the  prostate's  contribution  to  this  liquid,  the  function  of  which  is 
apparently  to  partly  coagulate  the  ejaculated  semen,  a  process  which 
occurs  also  when  sonen  is  placed  in  water.  I'he  respective  functions  of 
all  the  various  liquid  constituents  of  the  semen  are  as  yet,  however,  by 


IMPREGXATIOX 


439 


by  no  means  certain.  The  secretion  of  the  prostate  seems  to  preserve 
the  vitahty  of  the  spermatozoa,  while  that  of  Cowper's  <i;hiii(l  is  a  mucus 
which  prevents  their  too  wide  dissipation  in  the  vagina. 

The  amount  of  semen  deposited  in  the  fornix  at  each  coitus  depends 
on  the  vigor  of  the  sexuahty  of  the  male  and  on  the  time  since  ejaculation 
previously  occurred.  In  normal  cases,  that  is  when  coitus  does  not 
take  place  oftener  than  six  or  seven  times  per  month,  the  average  amount 
is  3  or  4  c.c,  but  it  may  be  much  larger  at  a  single  emission  and  much 
more  abundantly  produced.  In  old  men  semen  is  produced  many  years 
after  the  power  of  erection  and  intromission  has  gojie.  The  sperma- 
tozoa are  easily  killed  by  the  Rontgen  rays,  etc.,  and  in  some  cases 
spermatogenesis  appears  to  stop,  at  least  for  many  months.  In  young 
men  it  is  apparently  the  distention  of  the  seminiferous  tubules  with  the 


Fig.  251 


'i^/ 


.  ^^> 


Section  through  the  round  Hgament  cif  the  human  uterus.  (KoUiker.)  On  the  left  are  many 
bundles  of  cross-striated  muscle-fibers,  and  on  the  right  is  the  smooth  musculature.  la  the 
center  are  vessels.  Thus  we  see  that  the  movements  of  the  uterus  (as  in  coitus,  etc.)  may  be 
under  many  sorts  of  influence — perhaps  voluntary  as  well  as  reflex. 

constantly  secreted  sperms,  etc.,  which  raises  the  irritability  of  the  sexual 
nerve-centers  and  thus  leads  to  sexual  desire;  in  the  woman  these  condi- 
tions are  largely  lacking,  for  no  such  pressure  can  arise.  Under  the  influ- 
ence of  erotic  impressions,  nervous  or  imaginary,  the  semen  is  rapidly 
secreted  and  this  distention  may  become  almost  painful.  There  is  some 
evidence  that  semen  contains  some  substance  (enzyme?)  that  when 
absorbed  into  the  circulation  stimulates  metabolic  vigor.  This  action 
is  apparently  often  to  be  seen  in  the  physical  improvement  of  newly 
married  women. 

Fertilization  in  the  more  technical  sense  is  the  union  of  the  spermatozoa 
with  the  ovum.  This  leads  to  the  development  of  the  latter  into  a 
new  individual  possessing  the  characters  of  both  parents.  In  a  broader 
sense  it  is  the  woman  that  is  fertilized  not  bv  the  union  of  the  sexual 


440 


REPRODUCTION  AND  DEVELOPMENT 


elements  merely,  but  by  the  whole  generative  process.  It  is  one  of  the 
most  basal  instincts  of  the  adult  female  to  be  fertilized,  just  as  it  is  of 
the  adult  male  to  fertilize.     Next  to  that  of  self-preservation  this  is  the 


Fig.  252 


Fig.  253 


The  development  of  a  spermatid  into 
spermatozoon.  Figs,  a  to  /;  Zs,  cyto- 
plasm; k,  nucleus;  PC,  proximal  centro- 
.«ome;  DC,  distal  centrosome;  SF,  tail- 
thread.  Fig.  a:  Sk,  head;  Ekn,  end- 
nodule;  Val,  connecting-part;  Hst,  chief 
part;  and  Est.  end-part  of  tlie  tail.  fMeves.) 

strongest  of  all  our  instincts,  the 
cause  of  untold  happiness  and 
often  the  occasion  of  unimagined 
misery  and  crime. 

The  male  elements  of  the  seeds 
are  deposited  either  at  the  en- 
trance to  the  uterus  or  slightly 
within  its  neck.  The  next  in- 
quiry is  how  these  sperms,  two 
hundred  millions  or  so  of  which 
are  in  every  normal  deposit  of 
semen,  reach  the  distant  ovum  in 
the  further  end  of  the  Fallopian 

tube  or  on  the  surface  of  the  ovary.  The  alkaline  secretions  of  the 
mucosa  of  the  uterus  and  vagina  are  adapted  to  ])reserving  the  life  of 
the  spermatozoa  until  they  reach  the  tubes.  The  spermatozoon  is  an  in- 
dependent motile  rcll  with  a  very  long  and  active  flagelhim  (tail).  By  rapid 


p.  pr. 


Diagram  of  the  front  part  of  a  human  sperma- 
toiJzon:  Cp,  head  ;  CI,  neck  ;  Cd,  tail  ;  P. a., 
anterior  part  of  the  head;  L.  Gal.,  edge  of  the 
valve;  P.  p.,  posterior  part  of  the  head;  Nd.  a., 
anterior  nodule;  Ms.  int.,  mid-part  of  the  neck; 
AV/.  p..  posterior  nodule;  Spir.,  spiral  thread; 
Iiiv.,  involucrum  of  the  connecting  part,  P.  c; 
Mich.,  mitochondria;  Sh.  int.,  intermediary  sub- 
stance; Ann.,  annulus;  F.  pr.,  chief  thread;  Inv., 
involucrum;  P.  pr.,  chief  part  of  the  tail. 
(Meves.) 


IMPREGNATION  441 

undulations  of  this  fla<:;ellum  the  sperm  is  forced  ahead,  the  movements 
being  not  too  unlike  those  of  a  frog-tadpole  when  its  tail  is  at  its 
longest. 

In  the  chapter  on  Protoplasm  (see  page  43)  we  suggested  the  various 
forms  of  barotaxis,  or  reaction  of  certain  organisms  to  pressure,  and  found 
that  rheotaxis,  the  reaction  to  a  current  of  fluid,  was  a  common  cause  of 
movements  in  small  animals.  This  rheotaxis  apparently  helps  the  sper- 
matozoa to  pass  up  through  the  Fallopian  tubes  to  the  ova  or  ovum. 
As  has  been  already  said,  the  current  of  lymph  in  the  tubes  under  the 
influence  of  the  cilia  set  always  from  the  fimbriae  to  the  uterus.  If,  then, 
the  sperms  are  negatively  rheotactic  (that  is  accustomed  to  oppose  a 
current  rather  than  to  go  with  it),  we  have  a  tentative  explanation  of  how 
they  reach  their  goal  many  centimeters  away  from  the  uterine  cervix, 
where  they  are  mechanically  deposited  in  a  preservative  and  stimulating 
menstruum  (Adolfi).  Chemotaxis  also  may  aid  in  this  ascent,  for  in 
some  plants  it  is  the  chief  means  to  fertilization.  Hundreds  at  least 
of  the  spermatozoa  approach  and  surround  the  ovum,  and  the  place  of 
meeting  appears  at  present  to  be  usually  the  upper  part  of  the  tube. 
The  time  recjuired  for  this  passage  is  not  known,  but  it  is  probably  hours 
at  least  and  it  may  be  a  day  or  more.  The  sperms  appear  to  travel  in 
their  normal  liquid  about  150  mm.  per  hour,  but  we  have  no  evidence 
that  in  the  actual  and  devious  conditions  of  the  vagina,  cervix,  uterine 
body,  and  tubes  they  can  make  anywhere  near  this  speed,  especially 
because  of  the  strong  contrary  lymph-current  in  the  120  mm.  or  so  of  the 
tube.  As  frequent  ectopic  gestations  attest,  the  place  of  fertilization  may 
be  on  the  surface  of  the  ovary  sometimes  and  probably  in  any  other  part 
of  the  ovarian-uterine  path.  Inasmuch  as  the  location  of  the  ectopic 
growth  is  determined  by  the  arrest  of  the  descending  fertilized  ovum 
rather  than  by  any  condition  of  fertilization  itself,  the  usual  place  of  the 
latter  is  very  hard  to  learn  either  by  this  or  other  means. 

Oviposition  is  the  passage  of  the  fertilized  ovum  down  the  oviduct 
(in  woman  the  Fallopian  tube)  and  its  implantation  in  the  uterine  mucosa 
ready  to  develop.  In  birds  reptiles,  etc.,  the  egg  when  laid,  compared 
with  the  human  egg,  is  independent,  requiring  only  a  proper  environ- 
ment. All  placental  animals,  liowever,  lay  their  eggs  into  the  uterus,  a 
special  organ  of  development  and  birth. 

Fertilization,  as  has  been  said,  ordinarily  occurs  in  the  Fallopian  tube 
from  a  few  hours  after  a  fertile  coitus  up  to  perhaps  even  three  and  a 
half  weeks  (Diihrssen).  The  average  period  after  coitus  that  an  ovum 
is  fertile  is  estimated  by  Issmer  at  sixteen  days  (McMurrich).  It  will 
thus  be  seen  that  the  time  of  conception  (fertilization)  is  impossible 
of  exact  calculation  in  the  human  female  because  so  many  of  the  facts 
are  unknown.  One  large  group  of  cases  indicated  that  after  a  single 
coitus  the  average  length  of  pregnancy  was  275  days,  and  this  implies 
that  in  such,  usually  vigorous,  cases  fertilization  is  prompt  after  copula- 
tion. Ordinary  cases  in  which  coitus  may  take  place  at  all  times  in 
relation  to  menstruation  are  much  harder  to  calculate.     The  long  life 


442  REPRODUCTION  AXD  DEVELOPMENT 

of  the  sperm  and  ovum  after  coitus  would  seem  to  indicate  that  were 
all  the  concerned  organs  normal,  fertilization  would  almost  invariably 
follow  a  normal  copulation,  as  is  the  case  in  general  with  the  brutes  that 
are  the  less  artificialized  by  domestication. 

The  means  by  which  the  fertilized  ovum  is  transported  down  the  tube 
to  the  uterine  cavity  have  been  already  described.  The  cilia  lining  the 
different  divisions  of  the  tube  bear  it  along  at  a  slow  rate,  while  develop- 
ment goes  on.  Several  days,  probably  about  six  (2  cm.  daily),  are  re- 
quired for  the  ovum  to  reach  the  uterus,  which  meanwhile  has  been 
making  ready  for  it.  The  mucosa  of  the  uterine  fundus  has  hypertrophied 
and  become  soft  and  active  from  increased  vascularity,  and  the  blood- 
vessels extend  outward  to  form  long  villi.  This  new-growth  is  known  as 
the  decidua  vera,  and  it  forms  a  soft  nest  for  the  segmenting  ovum  when 
it  arrives  from  up  the  tube.  ]\Iean while  the  outer  covering  of  the  ovum 
has  been  changing  somewhat  similarly,  so  that  when  it  reaches  the  uterus 
its  villi  soon  interlock  with  those  of  the  uterus.  It  thus  becomes  in  a 
short  time  firmly  embedded.  Then  the  decidua  vera  grows  upward  about 
the  ovum  (forming  the  decidua  reflexa),  and  shortly  encloses  it.  The 
growing  ovum  is  embedded  firmly  in  this  way  in  a  soft  and  vascular 
matrix,  with  which  for  nearly  ten  lunar  months  it  can  develop,  growing 
meanwhile  after  an  inherent  pattern  of  its  o\vn  yet  influenced  more  or  less 
by  many  conditions  in  its  maternal  environment. 

PREGNANCY,  PARTURITION,  AND  LACTATION. 

Inasmuch  as  the  direct  influence  of  the  father  ceases  with  the  fertiliza- 
tion of  the  ovum,  we  may  now  turn  our  attention  wholly  to  the  means 
by  which  the  child  is  fostered  in  its  mother's  womb,  born  "into  the  world," 
and  nourished  until  fltted  to  eat  food  other  than  mother's  milk.  These 
three  processes  are  respectively  pregnancy,  parturition,  and  lactation,, 
and  because  the  subject-matter  of  an  art  and  science  by  itself  (obstetrics), 
thev  require  here  but  relatively  brief  discussion. 

Pregnancy  is  that  physiological  period,  in  round  numbers  forty  weeks 
long,  which  elapses  between  the  fertilization  of  Hie  ovum  and  the  begin- 
ning of  the  child's  expulsion  from  its  mother's  belly.  Too  often,  perhaps, 
it  is  looked  ujjon  as  other  than  a  normal  functional  part  of  a  woman's 
life,  but  biologically  woman  is  female  only  for  tliis  purpose. 

The  physiological  changes  which  occur  in  the  maternal  psychophysical 
organism  during  pregnancy  aftect  in  some  degree  nearly  all  its  aspects. 
We  may  divide  them  into  three  classes:  those  which  concern  respectively 
the  refjroductive  system  proper,  the  remainder  of  the  body,  and  the 
mind  (Edgar). 

The  changes  ix  the  reproductive  org.\ns  in  pregnancy  are  such 
as  one  would  expect  to  find  in  any  organic  apparatus  during  a  period 
of  functional  activity,  namely,  an  all-round  development.  The  body's 
changes  in  general  are  all  flirected  to  this  end  of  sui)porting  the  addi- 
tional activity  of  the  sexual  system. 


PREGXAXCY,  PARTURITIOX,   AXD  LACTATIOX 


4-1  ;:5 


.  Alterations  in  the  Body  Generally. — These  we  may  classify 
under  the  heads  of  changes  in  the  digestion,  circulation,  respiration, 
nervous  system,  urine,  thyroid,  and  skin.  This  is  only  a  classification 
for  convenience  of  description,  for  without  doubt  practically  the  whole 
organism  develops  to  meet  the  demands  made  on  it  by  its  production 
of  a  substantial  new  being  more  or  less  a  replica  of  its  mother. 

The  changes  wliich  the  dhjestive  function  undergoes  are  in  two  direc- 
tions: one  physiological,  an  increase  in  activity,  the  other  accidental  and 
scarcely  pathological,  an  increase  in  the  irritability  of  the  stomach  with 
a  hindrance  of  excretion  from  the  colon.     The  growing  fetus  and  the 


Fig.  254 


Sagittal  section  of  the  belly  of  a  woman  pregnant  two  months:  ut,  uterus;  dv,  decidua  vera; 
ch,  chorion;  am,  amnion;  dr,  decidua  refiexa;  h,  hemorrhagic  clot  between  chorion  and  reflexa 
(occurring  before  death?);   vs,  urinary  bladder.      (Ahlfelds.* 

enlarging  tissues  of  the  mother's  reproductive  apparatus  require  an 
increased  amount  of  nourishment,  especially  in  the  latter  half  of  preg- 
nancy, and  this  new  demand  brings  about  oftentimes  an  enlarged  appetite 
for  food.  This  is  more  noticeable  in  women  w^ho  do  not  usually  eat 
more  than  the  organism  requires,  although  probably  these  women  are 
to  be  found  only,  as  a  rule,  among  the  poorest  classes  of  Society.  The 
extra  food  demanded  by  the  pregnant  woman  is  especially  proteid  in 
nature. 

The  disturbances  of  digestion  appear  to  depend  on  the  growing  and 
congested  uterus,   which   irritates   the  abdominal  nerves  and  impedes 


444  REPRODUCTION  AXD  DEVELOPMENT 

intestinal  movement.  The  former  cause  results  in  nausea  ("morning- 
sickness")  lasting  sometimes  almost  from  conception  onward  even  for 
four  months  or  more.  Sometimes  it  brings  about  a  curious  craving  for 
all  sorts  of  unusual  articles  of  diet,  as  well  as  for  the  chalk, earth,  lime, etc., 
often  craved  by  young  children. 

The  blood  and  its  circidation  undergo  changes  of  much  less  practical 
importance.  The  changes  which  occur  are  less  than  was  formerly 
supposed;  for  example,  Ehrlich  denies  that  the  number  of  the  blood- 
corpuscles  is  changed  in  any  recognizable  degree.  Measurements  of  the 
erythrocytes  of  twenty-two  pregnant  women  (Rosthorn)  showed  no 
change  in  their  size,  although  there  were  many  of  a  diameter  greater  than 
normal.  Xo  nucleated  red  corpuscles  could  be  found,  yet  the  indica- 
tions were  that  regeneration  of  the  corpuscles  was  unusually  lively.  The 
percentage  of  hemoglobin  increases  slightly  and  considerably  (15  per 
cent.)  postpartum.  There  is  a  very  moderate  leukocytosis.  The  blood's 
alkalinity  is  slightly  lessened;  its  specific  gravity  is  unchanged  from  the 
usual  figure  (1055). 

It  is  likely  that  a  certain  amount  of  what  one  might  call  functional 
hypertrophy  of  the  heart  at  least  obtains  as  in  all  muscles  when  used 
more  actively  than  before,  but  its  degree  is  slight;  no  increase  in  blood- 
pressure  for  example,  is  discoverable.  The  heart's  apex  is  displaced 
upward  by  the  abdominal  pressure,  and  it  was  this  which  formerly  gave 
the  impression  of  enlargement.  The  right  heart  seems  to  be  under 
more  extra  strain  than  does  the  left  heart.  It  is  not  at  all  likely  (von 
Rosthorn)  that  any  pulse  exists  characteristic  of  pregnancy. 

Respiration  is  rendered  difficult  to  a  degree  dependent  on  the  increase 
in  size  of  the  abdomen.  Despite  the  additional  demand  for  more  oxida- 
tion made  by  the  fetus,  the  hypertrophied  uterus,  etc.,  the  inspiratory 
movements  are  more  or  less  impeded  by  the  presence  of  the  enlarged 
uterus  in  the  belly.  This  gives  rise  to  a  degree  of  dyspnea  that  is  usually 
however,  of  small  annoyance. 

The  nervous  system  during  pregnancy  becomes  both  more  sensitive 
and  more  irritable.  The  former  change  shows  itself  in  the  additional 
acuteness  which  the  senses  exhibit.  The  increase  in  irritability  is  mani- 
fest in  numerous  ways,  especially  in  "nervous"  primiparse,  for  conditions 
which  before  did  not  trouble  or  worry  tliem  now  become  occasions  of 
irritation. 

Changes  in  the  urine  are  many,  but  it  is  not  certain  that  they  may  all 
be  said  to  be  normal.  In  general  the  amount  is  increased,  with  a  corre- 
sponding decrease  in  density.  In  about  5  per  cent,  of  pregnancies  (some 
observers  say  many  more)  some  degree  or  other  of  albuminuria  is  to  be 
found.  Glycosuria  too  is  to  be  found  in  a  varialjle  percentage  of  preg- 
nancies. Acetonuria  is  to  be  found  in  all  cases  of  pregnancy,  but  in 
only  28  per  cent.  (Stolz)  does  its  degree  overstep  the  normal  figure.  The 
sulphates  of  the  urine  and  especially  its  phosphates  are  lessened  in  amount, 
being  used  perhaps  in  ff)rniing  the  fetus.  I'he  annnonia  of  the  urine 
increases  during  pregnancy. 


PREGNANCY,  PARTURITION,  AND  LACTATION  445 

The  skin,  especially  in  brunettes,  has  a  marked  tendency  to  show  an 
increased  deposit  of  pigment  in  its  lower  epidermal  layers.  The  areola 
of  the  breasts,  the  abdomen,  and  the  vulva  are  the  chief  areas  concerned. 
About  the  navel  there  may  l)e  deposited  a  ring  of  sigment,and  a  line  of 
similar  nature  two  or  three  centimeters  wide  tends  to  connect  the  mons 
and  the  sternal  cartilages.  Truzzis  supposes  these  pigmentations  to  be 
the  result  of  trophic  changes  set  going  reflexly  from  the  genital  apparatus. 
AMiite  lines,  more  or  less  circular  in  form,  coming  from  the  mechanical 
stretching  of  the  skin,  tend  to  appear  on  the  abdomen.  As  in  menstru- 
ation, skin-eruptions  tend  to  be  more  common  during  pregnancy.  The 
growth  of  hair  is  accelerated  or  stimulated,  as  is  also  the  production  of 
the  dermal  secretions  (sebum  and  sweat). 

The  thyroid  is  well  kno^^^l  to  swell  during  pregnancy  (as  after  coitus), 
resimiing  its  usual  size  after  labor.  The  exact  reason  for  this  hyper- 
trophy has  so  far  not  been  learned.  In  some  important  way  the  gland 
is  probably  closely  related  to  the  genital  functions  generally. 

Mental  Changes. — During  pregnancy  a  number  of  psychical  altera- 
tions occur,  and  as  we  do  not  know  fully  the  physical  basis  of  mind,  they 
must  be  mentioned  in  a  class  by  themselves.  They  are  of  no  little 
practical  importance  to  the  mother,  but  it  is  not  apparent  (despite  cen- 
turies of  superstition  to  the  contrary)  that  they  exert  any  influence  on 
the  offspring  within  her. 

With  the  increased  tendency  to  insanity  during  pregnancy  we  are  not 
concerned.  This  is  the  natural  result  of  the  additional  strain  placed  by 
pregnancy  on  a  nervous  system  already  burdened  with  a  more  or  less 
neurotic  taint.  These  effects  (melancholia  or  mania  for  the  most  part) 
are  more  common  in  unmarried  women,  the  mental  stress  being  then 
sometimes  unduly  great. 

The  psychical  changes  in  normal  women  while  pregnant  are  to  be  seen 
largely  in  the  affective,  or  emotional,  aspect  of  mind.  Sometimes  the 
whole  disposition  is  changed,  many  a  husband  finding  his  wife  happier 
and  more  ompanionable  while  pregnant  than  at  any  other  times.  But 
the  opposite  change  may  occur  and  women  usually  good-natured 
become  peevish,  irritable,  and  unhappy.  To  some  extent  the  causes 
of  these  changes  lie  in  the  woman's  mental  attitude  toward  children, 
toward  pain,  and  perhaps  even  toward  their  personal  safety.  Those  who 
look  forward  with  normal  delight  to  the  possession  of  the  promised 
child  will  in  general  be  happy  while  pregnant,  the  whole  organism  being 
dominated  by  the  child-forming  process.  To  many  even  strongly 
feminine  women,  however,  the  dread  of  the  unkno^^^l  experience  of 
labor,  with  its  usual  pain  and  usually  much  exaggerated  danger,  directs 
the  feelings  throughout  all  of  pregnancy,  and  makes  the  more  or  less 
obvious  bodily  inconveniences  worse  to  bear.  These  mental  changes 
are  none  the  less  important  because  not  exactly  definable,  and  form  no 
inconsiderable  part  of  the  phenomena  of  pregnancy  in  the  average 
civilized  woman.  As  regards  the  declining  birth-rate  in  many  regions, 
these   degenerative    mental    attitudes    of   women    are    more    important 


446  REPRODUCTIOX  AXD  DEVELOPMENT 

probal)lv  than  any  other  circumstance,  the  rate  being  lowest  in  just  those 
locahties  where  these  considerations  are  most  apt  to  be  depressive  and 
proliibitive  of  conception. 

Parturition. — This  is  the  complex  process  by  which  the  now  complete 
fetus  and  its  accessories  are  forced  into  the  world  from  its  mother's 
womb.  This  event,  the  especial  field  of  obstetrics,  we  need  discuss  only 
in  its  purely  physiological  aspects. 

Obstetricians  divide  the  process  of  birth  into  three  stages,  partly  for 
convenience  of  description.  The  first  stage  extends  from  the  first 
effective  contraction  of  the  upper  half  of  the  uterus  to  the  time  when  the 
OS  uteri  is  forced  open  enough  for  the  head  of'  the  child  to  pass  through 
it.  The  second  stage  lasts  from  then  until  the  child  is  fully  born.  The 
third  stage  comprises  the  expression  of  the  membranes  and  placenta. 
It  is  obvious  that  the  first  two  stages  are  physiologically  continuous  with 
each  other. 

The  causes  of  the  beginning  of  delivery  are  doubtless  several  in 
number,  but  are  all  included  under  the  term  ripeness;  on  the  other 
hand  the  occasion  of  the  commencement  of  the  event  may  be  any  one 
of  many.  Here  as  elsewhere  the  conditions  are  numerous  and  com- 
plex rather  than  single  and  simple.  On  the  average,  about  280  days 
after  the  beginning  of  the  last  menstruation  the  fetus  has  reached  ma- 
turity, and  then  the  metabolic  balance  between  the  oxygen  and  the  carbon 
dioxide  in  its  tissues  begins  to  lean  toward  asphyxia,  and  in  consequence 
the  placenta  begins  to  degenerate.  Thromboses  tend  to  form  in  the 
placenta,  and  soon  this  organ  begins  to  act  like  a  foreign  body  and  to 
break  away  from  the  uterine  wall.  Perhaps  the  excess  of  carbon  dioxide 
passed  into  the  maternal  medulla  oblongata  actuates  the  parturition- 
center  as  it  always  does  the  respiratory  center.  For  several  weeks  or 
even  months  prior  to  delivery  the  uterus  shows  painless  rhythmic  con- 
tractions, these  being  either  inherent  in  the  smooth  muscle-protoplasm 
or  directed  by  resident  ganglia.  Perhaps  the  placenta  and  fetus,  begin- 
ninirnowto  act  like  forei^jn  bodies,  stimulate  the  mother's  uterine  center 

•  •  •         A 

in  tiie  spinal  cord  so  that  the  rhythmic  contractions  mcrease  m  force  up 
to  the  effective  degree.  Such  being  perhaps  the  causes  of  the  beginning 
of  labor,  the  slightest  disturbance  of  the  nervous  apparatus,  of  the  cir- 
culation, or  of  the  muscular  (uterine)  nutrition  would  set  the  reflex  neuro- 
muscular mechanism  in  action.  Although  the  child  may  furnish  some 
of  these  exciting  conditions,  it  can  supply  little  or  nothing  of  the  motive 
power  for  its  own  extrusion  into  the  world. 

The  first  stage  of  actual  labor  begins  by  uterine  contractions  of  in- 
creasing severity.  As  is  probably  the  case  with  most  smooth-muscle, 
the  uterine  walls  liave  both  a  tonic  mode  of  contraction  and  a  rhythmic 
mode.  'J'he  former  tends  to  lessen  the  diameter  of  the  uterus  and  to 
keep  it  small,  while  the  latter  sort  of  contraction  is  the  slow,  progressive 
peristalsis  characteristic  of  all  the  tubes  and  sacs.  The  peristalsis  of  the 
uterus  in  labor  affects  only  the  upper  part  of  the  uterus  down  as  far  as 
the  "contraction-ring."    P^ach  "pain"  lasts  alK)iit  a  niiiuite,  bnt  they  recur 


PREGNANCY,  PARTURITION,  AND  LACTATION  447 

irregularly  rather  than  in  a  complete  rhythm,  and  each  is  harder  than  the 
preceding.  In  consequence  every  succeeding  contraction  gives  rise  to 
greater  pain  than  the  one  before  it.  The  first  pains  of  labor  are  caused 
by  the  violent  stinuilation  of  the  uterine  nerves,  whose  delicate  endings 
are  injured  by  the  strong  compression  of  the  hardening  uterine  walls. 
As  the  compressions  become  stronger  the  pain  is  radiated  over  the  abdo- 
men generally.  Each  peristaltic  wave  leaves  the  uterus  narrower  and 
in  consequence  longer  than  before,  but  the  pressure  in  the  sac  about  the 
fetus  does  not  reach  more  than  that  of  10  cm.  of  mercury.  The  liquid 
forms  a  sac  in  front  of  the  now  somewhat  advancing  head,  and  serves 
until  the  sac  ruptures  as  the  best  of  dilators  for  the  external  mouth  of 
the  womb. 

In  the  second  stage  of  labor  the  abdominal  muscles  are  put  in  action 
to  aid  the  uterine  contractions,  and  rhythmically  contract,  thus  powerfully 
pushing  from  above  upon  the  elongated  uterus  now  closely  pressing  the 
child  on  all  sides  save  in  front.  The  vagina  is,  then,  the  path  of  least 
resistance,  and  gradually  and  slowly  the  advancing  head  makes  its  way 
through  it  along  the  curve  of  the  pelvis.  At  last,  after  a  few  minutes 
of  excessive  pain  (properly  always  relieved  by  an  anesthetic),  caused  by 
the  over-stretching  of  the  nerve-filled  vulva,  the  relatively  rigid  head 
emerges  from  the  maternal  body.  The  softer  shoulders  and  body  so  on 
follow,  and  the  second  stage  of  labor  is  finished.  These  two  stages 
differ  greatly  in  length.  The  first  stage  averages  about  thirteen  hours 
in  primiparse  and  nine  hours  in  multiparse,  w^hile  the  second  stage  lasts 
about  one-and-one-half  hours  in  both.  Sometimes,  however,  the  first 
stage  lasts  two  days  or  more,  and  seldom  less  than  an  hour,  depending 
on  the  variable  relations  of  the  size  of  the  child,  of  the  pelvis,  and  the 
muscular  powers  of  the  mother. 

The  third  stage  is  the  expulsion  of  the  placenta  by  the  uterine  contrac- 
tions. It  is  usually  complete  within  ten  or  twenty  minutes  after  the  child 
is  born.  The  coming-away  of  the  placenta  gives  rise  to  more  or  less 
hemorrhage,  the  average  amount  being  about  400  c.c.  After  the  pla- 
centa is  delivered  the  uterus  normally  contracts  strongly,  thus  preventing 
further  and  dangerous  hemorrhage. 

The  muscular  phenomena  of  labor  may  occur  by  direction  of  the  spinal 
cord  alone,  for  the  whole  process  from  conception  to  delivery  is  possible 
in  dogs  whose  spinal  cords  have  been  severed  at  the  first  lumbar  vertebra 
(Goltz).  As  we  have  said,  the  movements  of  the  uterus  are  largely 
"automatic,"  but  are  regulated  and  adapted  by  the  inherent  nerves. 
They  may  be  initiated  by  reflex  impulses  from  any  part  of  the  reproduc- 
tive tract  (e.  g.,  the  nipples)  or  even  from  the  brain,  as  when  fright  causes 
miscarriage. 

Lactation. — After  the  muscular  and  mental  strain  of  labor  a  few  hours 
of  sleep  are  usually  necessary  and  are  very  beneficial.  The  child  being 
then  put  to  the  breast,  the  sucking-process  reflexly  causes  the  uterus  to 
contract,  thus  more  surely  preventing  hemorrhage.  It  also  removes  the 
colostrum  from  the  mammary  glands  and  makes  them  ready  to  secrete 


448  REPRODUCTION  AXD  DEVELOPMENT 

true  milk.  The  latter  begins  to  appear  about  twenty-four  hours  post- 
partum and  normally  becomes  abundant  within  the  next  day.  Nursing 
should  be  allowed  only  once  every  two  hours  between  six  in  the  morning 
and  the  mother's  bedtime  at  night,  and  only  once  in  the  night.  After 
six  or  seven  weeks  the  two-hour  period  should  be  lengthened  by  a  half- 
hour,  and  after  four  months  by  an  hour.  Once  in  three  hours  is  then  the 
most  beneficial  arrangement  for  both  mother  and  child,  and  night-feeding 
is  usually  unnecessary  after  the  first  four  months.  As  is  the  case  with 
other  neuro-muscular  mechanisms  (e.  cj.,  defecation),  the  habit  of  vigorous 
promptness  is  important  and  hence  nursing  should  be  accomplished  in 
fifteen  or  twenty  minutes,  and  from  each  breast  alternately,  one  breast  at 
a  meal.  Regularity  in  taking  food  is  of  very  essential  importance  to  the 
child,  the  danger  of  feeding  too  seldom  being  much  less  than  that  of 
eating  too  often. 

The  mother's  best  diet  for  large  and  adequate  milk-production  is  of 
the  ordinary  sort  save  that  it  should  be  generally  rather  more  abundant 
and  richer  in  proteid  (fresh  meats)  and  in  liquid.  Sufficient  muscular 
exercise  out-of-doors  is  important  in  maintaining  an  ample  milk-supply. 
A  large  proportion  of  the  infants  who  die  in  summer  from  intestinal 
disease  are  babies  fed  on  food  other  than  mothers'  milk. 


DEVELOPMENT. 

Our  concern  thus  far  in  describing  how  the  adult  racial  individuals 
are  reproduced  has  been  largely  with  the  parental  part  of  the  process. 
We  have  glanced  at  the  operation  of  the  generative  mechanism  and  have 
discussed  the  formation  of  the  egg  of  the  new  being  and  the  complicated 
way  in  which  it  is  made  fruitful.  Now  our  view-point  changes  somewhat. 
We  shall  look  at  things  hereafter  from  the  offspring's  stand-point  and 
make  it  our  business  to  outline,  if  dimly,  some  of  the  tangled  processes 
which  culminate  normally  (but  how  often  not!)  in  the  average  adult  man 
or  woman.  Forty  weeks  of  these  forty  years  the  new  being  passes  in  its 
mother's  womb,  and  meanwhile  is  physiologically,  even  if  not  morally 
and  legally,  a  part  of  its  mother's  being.  This  is  the  fetal  life.  From 
the  hour  of  birth  until  puberty  is  another  period  of  development,  about 
fourteen  years  long,  and  this  we  may  for  convenience  term  childhood. 
For  the  next  thirty  or  forty  years  or  less  maturiiy  keeps  up  a  somewhat 
variable  level  of  strength.  Beyond  this,  evolution  is  apt  to  become 
involution,  and  this  period  of  old  ar/c,  commencing  almost  imperceptibly, 
ends  inevitably  in  death.  Contrasting  the  human  adult  with  the  once- 
divided  ovum,  one  realizes  what  "development"  means.  Only  an 
expert  embryologist  could  tell  the  human  ovum  at  this  stage  from  that 
of  any  of  a  thousand  other  species,  yet  the  adult  man  or  woman  has  a 
physical  and  psychical  nature  which  is  unique  and,  taken  as  a  whole, 
the  summit  of  organic  evolution  on  the  Earth.  This  is  so,  however,  not 
becau.se  the  protoplasm  on  whifli  this  nature  is  somehow  based  is  superior 


DEVELOPMENT  449 

in  any  way  to  that  of  other  animals  and  plants,  but  l)ecau.se  this  human 
nature  t^oes  far  beyond  that  of  these  others  and  reaches  vahies  which 
are  prol)al)ly  both  permanent  and  real.  With  all  these  more  actual 
human  values  biology  as  such  has  nothing  to  do  save  to  recognize 
their  existence  and  to  admit  its  own  inadequacy  as  a  science  of  human 
nature. 

Fetal  Life  in  a  broad  sense  of  the  term  includes  the  period  of  develop- 
ment between  the  union  of  the  nucleoplasm  of  the  male  and  female 
pronuclei  and  the  completed  birth  of  the  child.  This  is  the  subject- 
matter  of  human  embryology,  and  partly  because  this  science  is  con- 
sidered a  portion  of  anatomy  rather  than  of  physiology,  we  do  not 
discuss  it  here. 

Childhood. — The  fourteen  years  or  so  between  birth  and  puberty  we 
may,  although  not  technically,  know  as  childhood.  Its  beginning  is  the 
separation,  for  the  most  part,  of  the  new  individual  from  its  mother's 
body.  Its  other  terminus  is  the  commencement  of  the  time  when  this 
new  being  may  in  turn  become  mother  or  father  to  another  generation. 
In  most  all  respects  childhood  merges  into  adulthood  gradually.  It  is 
only  in  the  reproductive  phase  of  bodily  function  that  entirely  new  events 
begin,  although  these  widely  pervade  in  one  way  or  another  both  the 
body  and  the  mind. 

The  commencement  of  childhood  so  far  as  the  various  bodily  functions 
go  is  likewise  gradual  in  some  respects.  Yet  the  unique  act  of  being 
born,  the  beginning  of  respiration,  of  digestion,  of  excretion,  the  changes 
in  the  circulation,  and  the  beginning  of  action  in  most  of  the  sense-organs 
make  the  extra-uterine  life  sufficiently  different  from  that  within  the 
womb.  Formerly  the  fetus  was  influenced  from  without  itself  almost 
wholly  (aside  from  mechanical  impacts  wholly)  through  the  mother's 
blood.  Xow,  however,  it  begins  a  much  more  variefl  career  and  becomes 
more  nearly  unified  with  its  environment  through  many  various  channels 
and  in  a  large  number  of  respects.  As  Fiske  long  ago  pointed  out,  it  is 
because  of  man's  uniquely  long  childhood  more  than  anything  else  that 
his  general  predominance  in  the  world  is  due,  for  meanwhile  he  imitates 
his  parents. 

The  ovum  has  increased  in  mass  more  than  nine  hundred  million 
times  by  the  time  the  child  is  bom,  and  has  seen  the  "division  of  labor" 
in  case  of  its  original  functions  go  on  in  hundreds  of  directions  and  in 
thousands  of  steps.  The  human  animal  when  Ijorn  (although  made  up  of 
cells  basally  like  the  ovum)  has  a  cellular  tissue-complexity  and  differen- 
tiation beyond  all  understanding.  At  the  birth  of  the  individual  these 
myriad"  cells  take  on  a  new  set  of  relations  to  each  other.  The  child 
begins  a  new  group  of  developmental  changes — his  long  second  step 
toward  maturity.  Let  us  glance  at  the  most  important  of  these  sorts  of 
growth. 

Weight.— The  average  weight  at  birth  of  the  female  child  of  American 
parents  is  about  3150  gm.,  or  7  lbs.,  and  that  of  the  male  child  is  100 
or  200  gm.  more.  Largely  for  the  reason  that  the  average  infant  assimi- 
29 


450  REPRODUCTIOX  AXD  DEVELOPMENT 

lates  little  nourishing  foot!  for  the  first  day  or  so,  its  weight  falls  in  two  or 
four  days  175  gm.  and  often  more.  In  babies  fed  from  vigorous  breasts 
however,  this  loss  is  often  much  less  or  even  none.  At  ten  days  old  the 
child  weighs  100  gm.  more  than  at  birth.  For  the  first  six  months, 
speaking  roundly,  the  infant  gains  25  gm.  daily,  and  for  the  next  six 
months  15  gm.  The  l)irth-weight  is  about  doubled  at  five  months  and 
trebled  at  fifteen  months.  When  a  year  old  the  child  weighs  9000  or 
9800  gm.  (20  to  21  lbs.),  and  this  weight  is  doubled  at  seven  years  and 
quadrupled  at  fourteen.  Breast-fed  babies  gain  in  weight  much  more 
regularly  and  certainly  during  the  first  half-year,  but  later  the  difference 
between  these  and  those  fed  from  the  bottle  with  modified  cows'  milk  is 
not  so  marked.  As  before  remarked,  the  liability  to  death  is  very  much 
greater  in  bottle-fed  infants,  especially  if  the  milk  be  improperly  modified 
and  cared  for. 

The  proportions  of  the  various  organs  differ  not  a  little  in  childhood 
and  adulthood.  Of  these  the  relative  weights  of  brain  and  spinal  cord 
to  the  body  are  most  conspicuous.  According  to  Bischoff,  the  brain  at 
birth  weighs  one-eighth  as  much  as  does  the  whole  body,  at  the  end  of 
one  year  one-sixteenth  as  much,  and  at  fourteen  one-twentieth  as  much. 
In  the  adult  the  brain  is  only  about  one  forty-third  of  the  body  by 
weight  Similarly  with  the  spinal  cord :  at  birth  it  is  one  five-hundredth 
as  heavy  as  the  body,  but  in  the  adult  only  one  fifteen-hundredth  as 
heavy.  This  relative  preponderance  of  the  nervous  system  is  clearly 
seen  in  the  conduct  of  the  child.  The  actuating  aspects  of  the  nervous 
system  are  especially  conspicuous,  while  its  inhibitory  functions  are 
relatively  little  developed 

The  liver  and  adrenals  are  relatively  large  in  childhood,  the  spleen 
relatively  small,  while  the  heart  bears  about  the  same  proportion  to  the 
body-weight  at  all  ages. 

Height. — The  average  length  of  babies  when  born  is  49  or  50  cm. 
In  a  year  this  has  increased  to  about  70  cm.,  in  two  years  to  79  cm., 
in  three  years  to  86.5  cm.,  in  four  years  to  93  cm.,  and  at  the  end 
of  five  years  the  average  height  is  almost  a  meter.  After  this  period 
the  child  grows  not  far  from  6  cm.  yearly,  so  that  when  he  or  she  is 
fifteen  the  height  is  just  about  treble  that  at  birth,  or  150  cm.,  its  doul> 
ling  having  occurred  at  the  begiiuiing  of  the  seventh  year.  Rotch  notes 
that  growth  in  height  is  fastest  in  the  spring. 

Nutrition  in  children  is  in  general  more  normal  and  vigorous  in  all 
directions  than  it  is  in  adults,  excepting  in  the  first  few  months.  The  full 
powers  of  the  digestive  enzymes  do  not  develop  all  at  once,  but  more  or 
less  gradually  in  the  first  third  or  half  of  the  first  year.  This  is  ])arti('U- 
larly  true  of  the  amylolytic  juices,  and  starch  is  particularly  ill-tligested 
in  the  first  months.  Normally,  that  is  in  woman's  milk,  the  only  carbo- 
hydrate ingested  is  lactose  or  milk-sugar.  In  general,  however,  the 
child  from  three  years  onward  digests  more  vigorously  than  the  adult 
does,  for  the  supply  of  digestive  juices  is  proportionally  greater  and  the 
alimentary  movements  more  active.     It  is  by  this  means  that  the  child's 


DEVELOPMEXT  451 

commissary  organs  are  able  not  only  to  replace  the  protoplasm  worn  out 
by  the  intense  youthful  activities,  but  to  do  more — to  cause  the  rapid 
growth  of  the  body.  As  we  have  just  seen,  this  causes  a  doubling  of  the 
body-weight  between  seven  and  fourteen  years.  The  child's  digestive 
system,  like  all  his  others,  is  more  plastic  and  more  adaptable  than  the 
adult's,  for  it  has  not  as  yet  become  habituated  to  certain  ruts  in  part  of 
mental  origin  but  always  in  the  nature  of  defect,  such  as  most  growTi-up 
persons  fall  into. 

Muscular  action  in  childhood  is  more  lively  but  inherently  less  accu- 
rate than  that  of  the  adult.  The  ultimate  usefulness  of  youth  lies  in  its 
ability  to  elaborate  the  neuro-muscular  mechanism  into  the  wonderful 
perfection  seen  in  the  capable  and  clever  adult.  All  know  how  vastly 
complex  is  this  machine,  and  how  countless  its  coordinations  and  its 
combinations  of  movement.  In  the  infant  up  to  four  months  or  so 
voluntary  movements  are  of  no  immediate  use  at  all,  for  they  are  so  much 
at  random  and  so  grossly  inexact  as  to  be  only  general  tendencies  of  action 
toward  some  object  or  end.  From  this,  the  merely  formative  stage  of 
neuronal  inter-knitting,  up  to  the  expertness  of  the  clever  craftsman  or 
performer  in  a  thousand  different  ways,  the  development  is  in  the  direction 
of  the  acquirement  of  better  and  ever  better  and  more  numerous  coordina- 
tions and  neuromuscular  adjustments.  For  this  the  new  individual 
was  created. 

The  circulation  during  childhood  differs  from  that  in  adult  life  chiefly 
in  its  irregularity  and  variability.  Especially  is  this  so  in  girls  and 
during  the  first  six  or  eight  years.  This  is  due  to  several  causes,  among 
which  are  the  greater  elasticity  and  variability  of  the  tissues,  particularly 
the  blood-vessels;  the  incomplete  development  of  the  circulation-regu- 
lating nerve-centers;  and  the  greater  irritability  of  the  nerves.  There 
is  often  a  better-marked  dicrotism  in  the  pulse  of  a  child  than  can  be 
found  in  adults,  due  doubtless  to  a  greater  elasticity  of  the  arterioles. 
The  pulse-rate  appears  to  lessen  from  its  beginning  early  in  fetal  life  (up 
to  about  seventy  years,  when  it  increases  slightly),  and  to  be  always  faster 
in  females  than  in  males.  As  was  said  above,  in  the  fetus  it  is  from  160 
down  to  110  or  so;  atone  year  it  is  about  110;  at  four  years,  100;  at  eight 
years,  85;  four  years  later,  SO;  and  in  adult  years  from  70  to  80.  For 
girls  the  rates  are  considerably  higher.  According  to  Vierordt  the 
circulation-time  at  birth  is  twelve  seconds,  while  recent  research  has 
shown  the  time  required  in  the  adult  to  be  about  forty  seconds.  There 
is  little  satisfaction  to  be  had  clinically  in  the  child's  pulse,  because  it  is 
so  variable  a  process  even  in  perfect  health,  especially  up  to  the  ninth 
or  tenth  year. 

Owing  to  the  more  active  muscular  life  and  metabolism  of  the  child, 
his  lijniph-floiv  is  livelier  than  that  of  adults,  and  the  vital  process  is 
correspondingly  strong  while  the  lymph-glands  and  the  lymph-vessels  are 
relatively  larger.  Digestion,  especially  of  fats,  is  relatively  better  in 
childhood,  and  the  lymph  takes  an  important  part  in  the  process  and  in 
nutrition  in  general. 


452  REPRODUCTIOX  AXD  DEVELOPMEXT 

Respiratio)i  during  childhood  diit'ers  hkewise  from  the  adult  process 
chiefly  in  its  greater  activity  and  in  its  larger  yariabilitv  under  different 
circumstances.  The  breath-moyements  are  more  diaphragmatic  and 
abtlominal  than  in  the  adult,  the  intercostal  muscles  being  relatiyely 
weak.  The  respiratory  movements  of  the  chest,  according  to  Uffelmann, 
are  at  birth  35  per  minute;  at  one  year  old,  27;  at  two  years,  25;  at  six 
years,  22,  and  at  twelve  years,  20.  Very  often,  indeed,  however,  one  sees 
breath-rates  averaging  five  higher  than  these  figures  indicate.  The 
breath-rhythm  is  very  vague  during  the  first  years  of  life,  and  varies 
greatly  from  little  causes,  such,  for  example,  as  emotions,  muscular 
activity,  and  physiological  variations  in  body-temperature.  Periods  of 
apnea  of  short  duration  are  normal,  while  the  rate  on  either  side  of  such 
a  period  may  vary  many  breaths  per  minute,  being  at  one  time  70  and  at 
another  40.  The  imperfect  connection  of  the  various  vital  centers  in 
the  medulla  plus  the  relative  strength  of  the  emotional  expressions  will 
in  part  explain  these  irregularities. 

The  bronchi  and  trachea  are  proportionally  larger  than  in  adulthood, 
while  the  alveoli  are  relatively  smaller.  Partly  because  of  this  we  find 
the  common  pneumonia  of  infancy  to  be  of  the  bronchial  type,  while 
that  of  middle  life  affects  the  alveoli  more  especially:  lobar  pneumonia. 

Body-temperature  is  another  function  of  the  child-organism  which  is 
characteristically  variable  and  irregular  by  the  adult  standards.  For  a 
few  days  after  birth,  owing  to  the  lessenmg  in  the  metabolism  from  lack 
of  assimilation,  the  degree  of  heat  may  fall  a  degree  or  so  below  the  daily 
average  of  about  37.2°  (99°  F).  Exposure  decreases  the  temperature 
readily.  Raudnitz  found  that  a  cold  bath  raised  the  temperature  (as 
indicated  in  the  rectum)  in  vigorous  new-born  children,  but  lowered  it 
in  feeble  infants.  If  we  take  37.2°  (99°  F.)  as  the  average  temperature 
of  the  first  ten  years,  it  must  be  considered  the  same  as  all  averages — 
that  is,  as  more  or  less  artificial.  The  causes  of  variation  in  temperature 
are  numerous,  and  many  of  these  in  childhood  frequently  produce 
effects  much  more  marked  than  they  would  among  adults.  Thus, 
excitement,  especially  mental  excitement,  and  intestinal  irritation  of  a 
trivial  degree,  weak  toxins,  or  fatigue  may  raise  the  temperature  of  the 
child  of  two  or  three  years  in  a  way  not  observed  in  the  child  of  ten  nor 
in  later  life.  This  great  variability  is  especially  marked  in  girls,  but  in 
both  girls  and  boys  it  constitutes  the  chief  peculiarity  of  the  temperature 
during  childhood.  A  temperature  of  39°  (102.2°  F.)  in  an  adult 
usually  means  something  of  consequence,  but  in  a  three-year-old  it  often 
.signifies  nothing  which  a  movement  of  the  bowels  will  not  promptly 
dispel.  Here,  as  elsewhere,  we  see  the  signs  of  neural  incompleteness 
and  of  nervous  instability. 

The  senses_  of  children  are  in  general  more  acute  than  are  those  of 
adults,  .save  in  so  far  as  training  is  involved  in  developing  the  actual 
sense-organs.  Sen.sations,  however,  by  themselves  are  of  little  use 
comparatively,  aside  from  their  meanings  to  the  individual.  The  child 
is  relatively  deficient  in  his  apperceptive  power  and  does  not  yet  know, 


DEVELOPMENT  453 

moreover,  how  to  use  his  senses  to  the  best  advantage.  Hence  the  effec- 
tive result  of  sensation  in  general  in  childhood  is  far  below  that  of  the 
adult,  although  the  latter's  actual  sense-organs  may  be  less  perfect  as 
mechanical  instruments  than  are  those  of  the  child.  (See  the  preceding 
chapter.) 

]\Iore  marked,  even,  than  the  bodily  characters  of  childhood  are  those 
of  the  Mental  Aspects  of  the  individual  when  young.  Into  these,  so 
amply  discussed  are  they  in  pedagogical  and  psychological  literature 
{e.g.,  by  Stanley  Hall),  we  cannot  go  here.  Three  principles,  however, 
may  be  mentioned  which  are  more  or  less  important  in  medicine.  First, 
the  young  child  lacks  mostly  whatever  degree  of  voluntary  control  over 
the  physiological  and  reparative  processes  the  adult  mind  exerts.  This 
makes  the  child  a  more  passive  and  more  plastic  patient  as  well  as  pupil. 
Its  physiology  is  perhaps  to  be  found  in  the  incomplete  command  over 
the  so-called  "voluntary"  musculature  which  is  so  conspicuous  an  aspect 
of  childhood.  How  far  this  control  extends  over  the  vegetative  func- 
tions in  the  clever  and  accomplished  adult  we  do  not  as  yet  commonly 
appreciate. 

The  child  is  relatively  naive  and  open  to  all  kinds  of  influences.  Habit 
in  this  period  of  life  has  not  yet  laid  its  all-encircling  and  resistless  fingers 
on  both  the  body  and  the  mind.  Children  therefore  are  more  amenable 
to  all  sorts  of  therapeutic  and  hygienic  measures,  and  especially  to  those 
which,  like  suggestion,  do  their  work  through  the  mental  processes. 

Worry  has  not  yet  fixed  its  hold  on  the  normally  cared-for  child.  In 
the  adult  this  is  a  source  of  harm  whose  importance  it  would  be  hard 
indeed  to  exaggerate.  Chronic  emotion  of  fear  as  worry  is,  its  asthenic 
effects  on  bodily  processes  are  certain,  and  none  the  less  so  because  the 
mode  of  its  action  is  not  fully  made  out.  It  is  hard  not  to  believe,  as  has 
been  suggested,  however,  that  worry  through  the  trophic  nerve-impulses 
depresses  the  metabolism  and  so  undermines  the  resistance  of  many 
kinds  of  tissue.  Working  in  the  opposite  direction  of  invigoration  and 
stimulation,  joy  and  happiness  exert  a  wholly  beneficial  eft'ect  on  the 
vital  functions.  Childhood,  normally  the  joyful  age  in  our  perhaps  too 
strenuous  civilized  life,  receives  the  full  benefit  of  this  continual  sthenic 
influence.  Not  a  little  of  the  versatile  freshness  of  the  child's  bodily 
metabolism  may  come  from  this  sort  of  mental  stimulation — as  it  may 
come  to  all  humanity  centuries  hence,  when  the  old-time  worries,  largely 
based  on  the  struggle  for  existence  and  gootl  health,  may  be  outgrown. 

Maturity  or  adulthood  is  the  general  subject-matter  of  ordinary 
physiology  and  needs  here  no  separate  discussion.  So  far  as  the  general 
activities  of  life  most  useful  to  the  world's  evolution  are  concerned,  it  is 
preeminently  the  period  of  achievement.  It  is,  for  example,  the  period 
of  reproduction,  biologically  one  of  basal  life-functions.  It  is  the  epoch 
of  the  bodily  strength  which  in  the  childhood  before  it  has  been  devel- 
oping and  which  in  the  senescence  after  it  will  gradually  lessen  again. 
This  gradual  accumulation  of  experience,  wisdom,  etc.,  during  the  period 
of  maturity  changes  the  nature  or  quality  of  the  individual's  capacity. 


454  REPRODUCTIOX  AXD  DEVELOPMEXT 

and  (as  when  one  wrongly  tries  to  compare  the  values  of  men  wdth  those 
of  women)  one  finds  comparison  therefore  between  maturity,  childhood, 
and  old-age  more  or  less  illogical  except  in  terms  of  bodily  strength  and 
the  somatic  functions.  These  latter  maturity  exhibits  at  their  best,  but 
no  one  should  fail  to  see  the  more  substantial  compensations  of  the  life- 
period  which  follows  it  in  a  portion  at  least  of  the  individuals  who  are 
born. 

Old-age  is  the  fourth  period  of  the  epochal  differences  which  we  need 
to  consider — and  the  last.  How,  physiologically,  does  it  differ  from 
the  average  status  of  maturity?  We  may  in  a  word  suggest  all  these 
differences  (save  as  has  just  been  mentioned)  by  the  term  decline,  "a 
bending-downward"  toward  death,  a  general  weakening  of  an  inherently 
limited  organism.  In  the  preeminent  respects  above  suggested,  then, 
senescence  is  a  superior  condition,  but  in  most  regards  it  is  the  inevitable 
decay  of  the  "  unremaining  glory  of  things  that  soon  are  old." 

The  iveicjht  and  stature  both  are  regularly  less  in  old-age  than  in  the 
epoch  of  maturity. 

The  causes  of  the  slowly  progressive  decrease  in  weight  are  chiefly 
the  lessening  of  the  water-content  of  the  skeleton;  the  disappearance  of 
the  fat  from  the  body  generally,  but  especially  from  the  muscles;  the 
skrinkage  of  the  muscles  (and  glands?)  from  their  relative  disuse;  and 
the  weakness  of  the  nutritive  process,  making  now  the  growth-balance 
negative  instead  of  positive,  as  in  childhood,  or  zero,  as  in  middle-life. 
Fat  represents  especially  the  storage  of  nutritive  tissue,  and  in  old  age, 
unless  the  digestion  be  unusually  vigorous,  this  surplus  is  not  produced 
and  stored.  The  bones  become  more  brittle  as  age  advances:  they 
lose  water,  collagen,  and  fat,  and  become  more  calcareous. 

The  reasons  why  the  aged  body  is  less  in  size  than  that  of  middle-age 
are  in  part  those  just  cited  as  explaining  the  loss  in  weight.  The  stature 
is  less  because  of  the  shrinkage  of  the  interosseous  cartilages  generally, 
and  especially  of  those  between  the  vertebrae.  These  plaques  lose 
collagen  and  chondrigen  and  in  so  doing  become  both  thinned  and  less 
elastic.  In  persons  accustomed  to  much  manual  labor  that  requires  a 
stooping  posture  the  spinal  column  has  acquired  a  dorsal  bend  which 
further  decreases  the  stature. 

Nidrition  in  old-age  shows  the  most  fundamental  differences  belonging 
to  this  epoch.  In  no  one  respect  especially,  but  in  all  of  them,  the  assimi- 
lative process  has  degenerated.  ]\Iastication  is  imperfect  because  few  or 
many  of  the  teeth  are  gone  or  broken.  Digestion  is  defective  pardy 
because  the  alimentary  movements  are  weakened  with  the  other  muscular 
activities  and  partly  because  the  digestive  liquids  have  no  longer  their 
former  abunrlance  or  (probably)  strength.  It  seems  likely  that  the 
failing  power  of  mastication  is  the  more  important  of  these  deficiencies, 
althf)Ugh  the  nnisfular  atoiiicityof  the  gut  must  be  also  a  weighty  factor, 
for  we  see  much  harm  coming  from  constipation. 

The  chemical  defects  if  any  in  the  digestion,  absorption,  assimilation, 
and  excretion    iMcidcnt   to  old-age  are  not  as  vet  well  known.     Habit 


DEVELOPMENT  455 

must  play  an  important  part,  for  it  extends  even  to  the  chemism  of  the 
nutritive  processes. 

Next  to  nutritional  defects  those  of  the  circulation  are  undoubtedly 
most  characteristic  of  old-age,  and  are  perhaps  even  more  frequently 
the  cause  of  death.  The  most  important  perhaps  of  these  changes  is 
the  sclerosis  or  hardening  of  the  arteries.  In  old  age  this  is  physiological 
rather  than  pathological,  and  is  always  present  in  some  degree  after  fifty. 
It  consists  of  an  atheromatous  condition  of  the  arterial  wall,  especially 
in  the  larger  tubes.  Sometimes  the  change  is  fibrous,  but  much  oftener 
calcareous,  the  essential  elasticity  of  the  arteries  being  in  either  case 
diminished  or  almost  lost.  This  makes  it  necessary  that  the  heart  should 
work  harder  to  keep  up  the  activity  of  the  capillary-circulation,  and  it 
therefore  becomes  enlarged.  Often  the  heart-walls  too  are  affected  in 
like  manner.  If  a  large  brittle  arteriole  burst  in  the  brain,  there  is 
apoplexy  and  resulting  death  sooner  or  later;  if  the  heart  gives  way  or  fails 
to  meet  the  demands  put  upon  it,  there  is  likewise  death,  either  at  once 
or  after  weeks  of  dropsy,  dyspnea,  etc.  Minor  degrees  of  these  conditions 
are  essentially  normal  after  old  age  has  begun,  but  that  they  would  be 
so  common  did  not  people  so  often  over-use  alcohol,  dissipate,  under-' 
exercise,  and  eat  too  much,  no  man  at  present  can  be  sure.  It  remains 
to  be  learned  through  statistics  whether  lactic  acid  (found  in  butter- 
milk) if  taken  continually  would  prevent  or  lessen  this  arterial  sclerosis 
so  frequent  among  people  more  than  fifty  years  of  age. 

The  pulse-rate  is  increased  in  old-age  five  or  ten  beats,  this  increase 
being  necessary,  as  well  as  the  heart's  hypertrophy,  to  compensate  for 
the  inelasticity  of  the  arteries. 

Body-temperature. — In  old  age  the  temperature  is  slightly  higher 
on  the  average  than  in  middle-age,  and  nearly  equals  that  of  infancy. 
This  is  brought  about,  despite  the  lessened  metabolism  of  advanced 
age,  by  the  decrease  of  vaso-motor  power.  The  peripheral  vessels  are 
relatively  more  rigid  and  smaller  than  in  middle  life  and  so  lose  less  heat 
from  the  blood  within  them  by  radiation;  and  less  sweat  is  produced. 
Despite  their  rise  of  temperature,  old  persons  usually  feel  chilly  unless 
their  environment  be  warm,  and  frequently  when  in  good  health,  even  in 
high  temperatures. 

Respiration  declines  in  old-age  largely  because  of  the  defects  in  the 
circulation,  but  also  because  of  the  hardening  which  the  costal  cartilages 
undergo,  and  also  from  the  weakening  of  the  intercostal  muscles.  Ex- 
piration especially  becomes  more  difficult  because  these  cartilages  are  less 
elastic.  This  is  one  reason  why  broncho-pneumonia  is  so  common  and 
fatal  in  old  persons:  the  difficulty  of  coughing  and  expectoration  allow 
the  irritating  mucus,  bacteria,  and  other  substances  to  collect  in  the  lungs. 

By  the  lessening  of  the  respiration  the  great  oxidative  process  of  the 
tissues  is  decreased.  This  is  one  condition  of  the  smaller  metabolism  so 
general  in  old-age:  the  fuel  is  lessened  and  the  vital  fire  burns  ever  more 
dimly  out. 

The  musrular  activity  in  old-age  is  greatly  diminished.     The  bones 


456  REPRODUCTIOX  AXD  DEVELOPMENT 

lose  tlieir  small  degree  of  pliancy,  the  tendons  and  cartilages  stiffen,  the 
muscles  lose  part  of  their  strength  and  their  power  of  endurance  because 
of  the  lessened  circulation  and  nutrition.  The  joints  move  with  more  or 
less  difficulty.  All  these  conditions  combine  to  decrease  to  a  minimum 
bodily  movements  of  a  voluntary  sort  and  to  lessen  the  activity  of  the 
vegetative  smooth  muscles.  In  addition  the  perfection  of  adjustment 
and  coordination  is  lost.  \^Tien  the  muscular  weakness,  is  considerable, 
the  graceful  balancing  of  youth  and  middle-age  at  last  gives  place  to 
a  trembling  and  uncertain  mode  of  movement  characteristic  of  very 
advanced  age  and  called  decrepitude. 

The  senses  undergo  changes  often  some  time  before  other  alterations 
are  apparent.  The  accommodation  of  normal  eyes  begins  to  lessen 
even  in  infancy,  and  by  fifty  years  the  lens  has  become  so  rigid  as  to 
necessitate  the  use  of  convex  lenses  in  order  that  near  objects  may  be 
clearly  seen.  The  general  hardening  of  tendons,  etc.,  has  by  sixty  years 
often  checked  the  free  adjustment-movements  of  the  ossicles  of  the  ears 
and  made  slightly  less  movable  the  membrana  tympani.  The  sense  of 
touch  is  regularly  blunted  and  that  of  pain  somewhat  so.  In  general 
the  mental  processes  are  slowed  and  rest  becomes  natural  in  larger  pro- 
portion than  formerly,  in  a  way  corresponding  to  the  lessened  strength. 

Death.— Physiologically,  death  is  not  development  but  the  cessation  of 
development  and  of  that  "continual  adjustment"  and  ceaseless  chemical 
and  physical  change  in  which  bodily  life  essentially  consists.  Metabolism 
stops  and  thereupon  the  former  protoplasm  is  no  longer  protoplasm 
but  only  animal  matter  liable  at  once  to  that  retrograde  series  of  changes 
which  ends  in  distributing  the  elements  of  the  former  organism  into  other 
shapes,  whether  living  or  dead. 

There  are  two  sorts  of  death,  corresponding  to  the  two  orders  of  units, 
the  cell  and  the  individual  animal.  Let  us  look  briefly  at  cellular  death 
first. 

The  essential  thing  about  the  death  of  a  protoplasmic  cell  is  the  cessa- 
tion of  its  metabolism,  because  it  is  in  that  process  largely  that  life  inheres. 
AYhether  the  nucleus  or  the  nucleolus  or  the  centrosome  or  none  of 
these  organs  controls  the  cell's  activities  we  do  not  as  yet  know,  and  hence 
we  can  state  nothing  as  to  the  process  of  its  death.  Pathology  is  that 
branch  of  l)iology  which  discusses  the  various  steps  toward  death  to 
which  cells  are  liable,  and  to  the  text-books  of  that  science  the  reader  is 
referred  for  the  facts  and  theories  as  to  cytological  death.  The  important 
thing  for  us  here  is  that  cell-death  of  one  sort  or  another,  in  one  organ 
or  another,  is  always  the  cause  of  the  death  of  the  entire  individual,  the 
liiglier  unity,  just  as  in  turn  a  race  dies  only  from  the  death  or  decay  of 
the  individuals  composing  it.  ^\lien,  as  always  happens  in  all  animals 
.save  unicells,  the  death  of  some  cells  precedes  that  of  others,  we  have 
the  conrlition  termed  by  Schultz  necrobiosis  (death-in-life).  Poikilo- 
tliermf)us  animals  show  this  process  best,  and  it  is  because  of  it  that 
frogs  and  turtles  and  batrachians  generally  are  so  useful  to  humanity 
for  studying  some  of  the  conditions  of  life.     Momotherms  die  all  over 


DEVELOPMENT  457 

much  more  rapidly.  This  is  apparently  due  to  their  more  elaborate 
nervous  systems  in  part,  but  chiefly  to  the  fact  that  when  the  circulation 
stops,  body-temperature  rapidly  falls,  and  this  disturbs  in  many  ways 
the  osmotic  and  chemical  metal^olism.  Even  in  mammals,  however,  cer- 
tain sorts  of  protoplasmic  activity  continue  a  considerable  time  after  the 
animal  as  an  individual  is  dead.  Thus,  the  cilia  keep  up  their  rhythmic 
swaying  three  or  four  days,  and  the  leukocytes,  still  more  independent, 
continue  their  ameboid  movements  for  a  week  or  more,  these  being  still 
surrounded  by  their  usual  nutriment,  the  plasma.  Just  in  proportion, 
then,  as  a  cell  is  immediately  dependent  on  its  environment  for  nutriment, 
heat,  and  removal  of  its  waste,  does  its  death  closely  follow  the  cessation 
of  the  circulation  and  of  the  respiration.     (See  Expt.  51  in  the  Appendix.) 

Hibernation  has  to  be  thought  of  as  a  partial  cessation  of  cell-life,  for 
the  circulation  and  respiration  {i.  e.,  nutrition)  then  continue  only  in  a 
very  restricted  manner.  As  we  have  seen  already,  human  hibernation 
is  sometimes  induced  voluntarily,  as  by  the  fakirs  of  India.  Even 
normal  sleep  perhaps  is  a  low  degree  of  this  lessening  of  the  general 
cellular  activity  of  the  organism. 

On  the  other  hand,  the  exact  biological  status  of  the  dried  state  in 
which  certain  minute  animals  of  our  aquaria,  notably  Tardigrada,  can 
pass,  remain  months,  "or  even  years,"  and  yet  revive  readily  on  being 
immersed  in  water,  is  at  present  quite  unthinkable.  It  is  unlike  death 
as  at  present  defined  by  biologists,  but  yet  it  seems  to  fail  of  the  death- 
conditions  only  in  its  persistence,  the  non-decay  of  its  protoplasm,  and 
in  its  power  of  recovering  the  usual  activities  of  life.  This  state  seems  to 
imply  that  it  is  only  the  decomposition  of  protoplasm,  its  katabolism 
unaccompanied  by  anabolism,  that  prevents  the  continuance  of  life  so 
long  as  body-decay  can  be  prevented  and  its  protoplasm  be  still  unpoi- 
soned.  But  so  long  as  we  do  not  know  as  yet  whether  what  we  call  life 
is  a  uniform  thing,  essentially  alike  from  Haeckel's  "monera"  to  man, 
or  whether  it  may  not  be  of  many  sorts  rather,  nothing  worth  the  reading 
need  be  speculated  in  this  direction.  The  phenomena  of  complete 
drying  followed  by  revival,  however,  suggest  strongly  that  in  the  tardi- 
grades,  etc.,  at  least,  the  cessation  of  cell-metabolism  may  not  mean  the 
death  of  the  individual  animal.     (See  Fig.  129,  p.  236.) 

The  nature  of  individual-death  has  already  been  suggested  in  the 
foregoing.  It  is  a  less  scientific  term  and  a  more  practical  and  legal 
expression.  Oftentimes  a  person  thought  dead  is  not  so,  but  very  seldom 
is  a  person  who  really  is  dead  supposed  alive.  On  this  account  the  danger 
is  considerable  and  the  means  of  knowing  when  an  individual  is  really 
dead,  that  is  unrevivable,  are  important,  and  that  too  aside  from  the 
legal  relations  of  the  problem. 

The  common  law  generally  recognizes  a  person  as  dead  when  his  heart 
has  ceased  to  beat.  As  we  have  seen  recently,  the  heart  is  about  the 
first  organ  to  begin  to  move  in  the  fetus,  and  in  Daphnia,  for  example, 
on  drying  up  it  is  the  last  to  die.  This  presumption  that  the  cessation 
of  the  pulse  or  of  the  apex-beat  is  the  forerunner  of  death  is  a  proper 


M5S  REPRODUCTION  AND  DEVELOPMENT 

and  usually  a  precise  one.  Life  is  mostly  dependent  on  metabolism,  and 
this  in  turn  immediately  on  a  supply  of  nutriment  and  of  heat,  and  on 
a  prompt  removal  of  katabolic  waste.  The  instant  the  circulation  all 
over  the  body  stops  metabolism  with  certain  exceptions  comes  at  once 
to  a  standstill.  The  brain  is  especially  dependent  from  second  to  second 
on  a  rapid  stream  of  normal  blood.  Suppose  a  person  in  the  standing 
position  to  be  shot  with  a  large  bullet  through  the  heart,  or  that  the 
heart  of  a  man  with  myocarditis  bursts  or  stops  short  in  extreme  diastole. 
In  any  of  these  cases  the  skeletal  muscles  instantly  lose  their  tone  because 
the  vast  multitude  of  impulses  which  pass  continually  from  the  motor 
centers  to  these  sustaining  muscles  immediately  cease.  As  a  result  the 
man  drops  almost  instantly  when  the  blood-stream  has  ceased,  and  that 
is  immediately.  In  parts  of  the  body  other  than  the  nerve-centers  the 
effective  metabolism  continues  somewhat  longer,  and  yet  not  long  enough 
to  sustain  the  body-heat  for  any  appreciable  time,  for  the  body  cools 
much  as  would  one  artificially  heated  when  the  source  of  heat  is  removed. 
Recent  work  on  the  heart  has  shown  that  in  cases  where  the  organ  is 
not  materially  injured  (as  from  lightning-stroke  or  from  blows  over 
the  solar  plexus)  it  may  be  often  started  beating  again  by  cardiac 
massage  either  directly  or  through  the  pericardium.  This  indicates  that 
the  nervous  inhibitory  shock  has  no  permanent  influence  over  the  heart's 
rhythmic  pulsations.     (See  Expt.  15  in  the  Appendix). 

Respiration  is  another  function  whose  cessation  promptly  kills,  but 
it  does  not  do  so  as  quickly  as  the  stasis  of  the  circulation,  for  survival 
sometimes  occurs  after  the  intake  of  air  has  been  stopped  for  as  long  as 
five  minutes.  The  modes  of  death  other  than  nervous  shock,  the  stopping 
of  the  pulse,  and  the  cessation  of  breathing  we  need  not  consider.  It  is 
already  obvious  how  individual  death  differs  from  cellular  death.  The 
former  term  means  the  end  of  the  general  faculties — movement,  sensa- 
tion, posture,  etc. — of  the  whole  organism  so  far  as  appears  from  without. 
The  latter  expression  means  the  really  essential  physiological  death. 
Individual  "death"  may  sometimes  be  recovered  from;  cell-death,  so 
far  as  we  know,  never. 

Physiology  has  at  present  no  concern  with  the  chief  personal  problem 
of  the  human  race — persistence  after  death.  This  subject  even  psy- 
chology still  almost  ignores,  and  scientific  ethics  knows  next  to  nothing 
of  it.  Death,  indeed  still  "the  Arch  Fear  in  a  visible  form"  to  many 
unthinking  men,  must  from  considerations  other  than  these  receive  its 
quietus  in  the  soul  of  Iminanity. 


APPENDIX. 


Containing  directions  for  performing  certain  fundamental  physi- 
ological experiments,  with  brief  theoretical  notes  on  the  same;  a  list  of 
topics  suitable  for  essays  and  conference-discussion;  and  conversion- 
tables  of  various  sorts. 


LABORATORY  PHYSIOLOGY. 

The  following  pages  relating  to  the  work  in  practical  physiology  in 
the  laboratory  contain  some  of  the  theory  underlying  the  experiments, 
but  more  must  be  obtained  from  the  text-books  in  which  adequate  dis- 
cussions of  all  important  matters  are  set  forth.  There  follow  also  con- 
cise, but  indispensable,  directions  for  doing  in  an  orderly  and  scientific 
way  numerous  basal  experiments,  together  with  the  physiological  prin- 
ciple which  it  is  the  chief  purpose  of  each  experiment  to  demonstrate. 
To  do  the  laboratory  work  without  a  full  understanding  of  its  various 
theoretical  relations  would  be,  of  course,  only  the  training  of  an  artisan. 

Every  experiment  is  to  be  performed  successfully  and  well  before  the 
next  is  taken  up.  To  prove  that  this  guiding  rule  of  the  laboratory  is 
lived  up  to,  every  experiment  is  to  be  demonstrated  at  the  time  it  is  being 
done  to  the  instructors  in  charge,  or  when  the  graphic  method  is  employed, 
evidence  to  the  same  effect  in  the  form  of  the  original  curves,  properly 
labelled  in  all  their  details,  pasted  into  the  note-books.  The  excellence 
of  these  curves  recorded  in  the  note-books  largely  determines  the  standing 
of  the  respective  students  in  the  important  practical  part  of  the  Course, 
but  good  notes  are  next  in  importance  to  good  curves.  These  are  to  be 
written  in  the  laboratory  directly  from  the  experiments.  ^Nlake  notes, 
then,  and  not  pictures  merely,  which  shall  record  your  own  observations. 
You  have  to  use  your  common  sense  all  the  time! 

I.  PROTOPLASM  AND  SIMPLE  ANIMAL  FUNCTIONS. 

The  first  work  in  the  laboratory  consists  of  a  series  of  careful  observa- 
tions with  the  compound  microscope  of  a  number  of  selected  animal- 
cules. We  do  this  chiefly  for  two  reasons,  the  first  that  you  may  become 
familiar  with  protoplasm  in  its  less  differentiated  forms  (the  human 
body  consists  of  highly  differentiated  protoplasm).  The  other  reason  is 
that  each  of  these  animals,  however  small,  exhibits  all  the  basal  functions 


460  APPENDIX 

possessed  by  any  animal,  yet  in  a  form  so  simple  as  to  be  much  more 
readily  analyzed  and  appreciated  than  is  possible  in  the  most  evolved 
forms.  The  life  of  any  order  and  species  of  plant  or  animal  is  as  perfect 
as  that  of  any  other. 

There  is  here  immensely  much  to  be  seen  by  him  who  has  brain  and 
eyes  to  see  it,  and  life  is  one,  apparently,  whether  in  infusorium  or  in 
man. 

"  Flower  in  the  crannied  wall, 

I  pluck  you  out  of  the  crannies; 

Hold  you  here,  root  and  all,  in  my  hand, 

Little  flower — but  if  I  could  understand 

What  you  are,  root  and  all,  and  all  in  all, 

I  should  know  what  God  and  man  is." 

Each  student  will  get  out  of  the  laboratory  work  in  physiology, 
and  especially  out  of  this  first  portion  of  it,  that  which  he  is  fitted  by  his 
intelligence,  training,  and  industry  to  acquire. 

Experiment  1. — The  first  slide  given  out  contains  some  of  the  simplest 
forms  of  living  vegetal  and  animal  cells.  The  vegetal  cells  are  here  grow- 
ing filaments  of  a  common  alga,  Spirogyra,  or  of  another  still  more 
common,  called  Edogonium,  seen  as  lines  made  up  of  rectangular  yellow- 
ish cells  more  or  less  filled  with  protoplasm  colored  green  with  chlorophyll 
(plant-green).  Use  first  a  No.  3  objective  to  find  a  filament  made  up  of 
cells  as  large  as  possible.  Note  the  geometrical,  rigid  structure  of  the 
cellulose  cell-walls,  and  that  the  cells  are  lacking  in  means  of  locomotion. 
Now  employ  a  No.  5  objective  and  draw  in  the  note-book  any  changes 
observable  in  the  arrangement  of  the  essential  living  protoplasm  within 
the  cells.     ]\Iake  large  drawings  of  all  observed  detail. 

Compare  with  these  vegetal  cells  the  minute  infusoria  rapidly  swimming 
about  them — animal  unicells  made  up  wholly  of  soft  protoplasm  not 
confined  in  rigid  cellulose  walls.  Note  that  the  animal  protoplasm 
proljably  is  uncolored  by  the  green,  hemoglobin-like  pigment  chlorophyll; 
a  lack  which  prevents  animals  from  synthesizing  starch  out  of  its  inor- 
ganic elements.  Note  their  rapid  movements,  in  search  of  food,  by 
means  of  cilia;  and  that  they  seldom  or  never  quite  collide  with  each 
other.  Observe  if  possible  individuals  each  about  to  divide  into  two 
new  animals  smaller  than  their  parents  but  otherwise  similar.  Make 
numerous  drawings  showing  all  possible  details.     (See  Chapter  I.) 

In  a  mixture  such  as  this  practically  only  on^  thing  usually  distin- 
guishes plants  from  animals,  and  that  is  the  presence  of  the  green  pig- 
ment chlorophyll.  The  usual  criterion  of  animality  employed  for  higher 
forms,  the  rapid  movements,  will  not  answer  with  these  simple  forms 
of  life,  for  some  of  the  green  plants  have  active  swimming  movements 
and  some  of  the  animals  are  motionless  and  green  (see  Euglena). 
Still  many  plants  contain  no  chlorophyll — and  there  is  left  no  strict 
standard  whatever  for  discriminating  a  plant  as  such  from  an  animal. 

Expt.  2. — The  second  allotment  consists  largely  of  a  very  much  mixed 
mass  of  common  saprophytic  bacteria  and  cocci  which  grow  on  nutritious 


PROTOPLASM  AXD  SIMPLE  AXLMAL  FUXCTIOXS  401 

liquids  wlien  exposed  to  the  air  and  li<j;ht.     Observe  the  minuteness  of 
these  vegetal  cells;  their  vast  multitude  and  Uieir  spontaneous  movements. 

For  knowledge  of  the  bacteria  see  the  text-books  on  bacteriology. 

Expt.  3. — The  third  slide  contains  the  important  protozoan  rhizopod 
Ameba  proteus.  (See  Chapter  I.)  Use  a  low-power  (two-inch)  objective 
to  find  one  of  these,  the  simplest  of  living  an  imals.  Note  its  transparency, its 
extreme  simplicity,  the  nucleus,  the  metaplasm,  and  the  vacuoles.  Watch 
its  slow  creeping  along  the  slide  and  their  quite  characteristic  and  unique 
use  of  protoplasmic  streaming  into  pseudopodia  for  locomotion,  and  for 
surrounding  food-particles.  Observe  how  it  tends  to  contract  in  area 
on  being  stimulated  and  that  it  gradually  extends  numerous  pseudo- 
podia again  when  allowed  to  rest.  No  cell-wall  can  be  discovered. 
Observe   food-prehension   and   vacuole-bursting. 

^lake  drawings  of  as  many  shapes  of  one  ameba,  in  definite  successive 
periods,  as  possible.     If  necessary,  use  tlie  warm-stage. 

This  observation  of  Ameba  (because  the  type  of  relatively  independent 
undifferentiated  protoplasm)  is  one  of  the  most  important  experiments 
possible  in  class-work  in  physiology.  Here  is  the  very  essence  of  spon- 
taneous vital  activity.  Do  not  miss  obtaining  much  from  it  in  the  hours 
allotted  to  it.     See  text-books  of  biology  for  details. 

Expt.  4. — ^The  fourth  allotment  on  the  slide  contains  one  or  more 
species  of  the  ciliated  infusorium  Paramecium.  Use  first  the  No.  3 
objective  and  observe  this  unicell's  mode  of  poking  about  among  the 
vegetal  and  mineral  debris  in  search  of  food,  much  as  fishes  do.  Note 
its  various  movements,  backward  and  forward  with  almost  equal 
facility;  its  mode  of  turning  shows  well  the  fluidity  of  the  protoplasm.  A 
large  paramecium  is  said  to  weigh  about  0.00017  mgr.  and  to  be  capable 
of  raising  0.00158  mgr. 

Now  adjust  the  No.  5  objective  and  kill  the  animals  by  gentle  heat  or 
poison  them  with  a  drop  of  a  1  per  cent,  chloral  hydrate  solution,  which 
gradually  slows  their  movements  without  quickly  killing  and  disinte- 
grating them.  Observe  among  other  things  their  ciliary  movements  and 
the  various  elemental  organs  within.  ^Nlake  careful  drawings  of  these 
animals,  with  all  discernible  detail,  at  intervals  if  necessary  to  indicate 
changes.  Paramecium  merits  all  the  observation  and  study  that  may 
be  put  upon  it.  Parker  in  his  Biology  has  an  excellent  description  of 
this  animal  as  well  as  of  others  of  like  interest.  See  Jennings  for  the 
mental  processes  of  Paramecium,  and  Conn. 

The  infusoria  are  so  named  because  they  appear  in  multitudes  in  the 
course  of  a  week  or  two  in  infusions  of  hay,  dead  leaves,  and  similar 
nutritious  substances.  Ameba  is  the  most  difficult  to  be  sure  of  having 
at  any  given  time,  and  Stentor  is  often  scarce;  but  Vorticella,  Tubifex, 
the  Rotifers,  Cyclops,  and  Daphnia  (the  second  a  worm  and  the  two 
last  crustaceans)  can  generally  be  found  in  balanced  aquaria  from 
which  fish  and  large  larvte  are  absent.  Cyclops  and  another  crustacean, 
the  bivalved  Cypris  (of  little  use  to  us  because  its  shells  are  opaque), 
are  much  easier  to  keep  year  after  year  than  is  Daphnia;  nearly  every 


4()2 


APPENDIX 


permanent  pool  contains  these  forms  in  abundance.  Ameba  readily 
persists  year  after  year  in  aquaria  where  fish  are  present,  although  they 
disappear  at  times  temporarily. 

Expt.  0. — ^The  fifth  specimen  is  a  remarkable  ciliated  infusor  named 
VorticcUa.  We  have  already  probably  seen  early  stages  in  the  develop- 
ment of  this  animal  as  small  spherical  transparent  masses  of  protoplasm 
rolling  about  through  the  drops  of  water  on  the  previous  slides.  A 
later  stage  shows  a  circular  fringe  of  cilia  developed  on  one  side  of  these 
spherules  and  a  pointed  short  projection  on  the  opposite  side  of  the 
animal.  A  still  later  stage  shows  animals  with  this  process  developed 
into  a  long  contractile  filament,  the  muscle-stem  of  this  unicell,  which 

Fig.  255 


Vorticella,  showing  various  phases  and  the  modes  of  reproduction:  (1)  A'^,  maeronucleus;  n, 
micronucleus;  cv,  contractile  vacuole;  jv,  food  vacuole;  m,  gullet;  v,  vestibule;  (2)  an  encysted 
phase,  with  3,  its  mode  of  division;  4,  a  free-swimming  unit  dividing  off;  5,  formation  of  sev- 
eral small  units  (tng);   6,  conjugation  of  a  small  zooid  (mg)  with  one  of  larger  size.      (Butschli.) 


the  vorticella  drags  behind  him  as  he  rapidly  sucks  his  way  through  the 
water  by  means  of  the  cilia  at  the  vortex.  Soon  a  sort  of  hook  develops 
at  the  end  of  this  filament  and  catches  upon  some  mass  of  vegetal  matter 
and  thus  anchors  tiie  animal  for  the  rest  of  its  life  of  a  few  days.  Draw 
all  tiiese  forms.     See  also  if  possible  the  cf^lony-form,  Zoofhamnium. 

Observe  in  the  anchored  variety  of  Vorticella  (1)  the  vortex  of  water 
(and  contained  food)  passing  into  the  animal;  (2)  the  internal  organs; 
(3j  the  very  quick  si)iral  contrMction  of  the  stem-muscle  when  the  animal 
is  jarred  or  otherwise  stimulated;  (4)  the  gradual  probably  passive 
extension  of  the  animal  on  the  end  of  the  uncoiling  stem;  and  (5)  that 
the  muscle  soon  becomes  fatigued  and  fails  to  respond  to  stimulation. 


PROTOPLASM  AND  SIMPLE  AXLMAL  FUXCTIOXS  463 

Count  the  number  of  spontaneous  contractions  of  the  more  or  less 
rhythmic  smooth  muscle  of  the  stalk  occurring  in  ten  minutes.  (See 
Compter  Rcndus  Soc.  dc  Biol,  1904,  Ivi,  p.  704.) 

The  difficulty  of  defining  individuality  is  finely  shown  by  a  comparison 
of  Vorticella  and  Zoothamnium. 

Expf.  6. — The  next  specimen  (to  be  studied  with  objective  3  first  and 
then  with  5)  is  Sfoiior.  This  infusor  is  more  clumsy  and  many  times 
larger  than  Vorticella,  but  has  the  same  general  mode  of  life.  The  con- 
tractile stem  in  this  case  is  surrounded  with  cytoplasm  largely  lacking 
in  ^"orticella.  The  internal  movements  of  Stentor  are  produced  by  the 
simplest  sort  of  muscular  fibrillse  longitudinally  arranged  about  the 
periphery  of  the  thick  body-stalk.  The  animal  sometimes  secretes  a 
delicate  temporary  cup-shaped  shell  about  its  foot,  into  which  it  quickly 
withdraws.     Some  forms,  however,  are  free-swimming  only. 

Expt.  7. — Eufjlena  (viridis). — This  is  a  unicell  of  the  flagellate  sort 
from  O.Oo  to  0.15  mm.  in  length.  As  its  name  implies,  it  is  brightly 
green  and  it  is  one  of  the  organisms  which  sometimes  color  stagnant  water. 
This  infusorian  has  a  cell-wall  (cuticle) — note  how  it  limits  the  shapes  of 
the  animal  as  compared  with  Ameba.  Its  movements  are,  however, 
various  and  characteristic.  Euglena  contains  granules  of  some  carbo- 
hydrate. The  chlorophyll  is  contained  in  one  or  more  chromatophores 
at  the  body-center.  The  bright  red  spot  near  the  anterior  (flagellated) 
end  is  the  eye — a  mass  of  pigment  which  can  make  the  animal  aware 
only  of  degrees  of  light  and  shade.  The  flagellum  arises  from  the  bottom 
of  the  mouth  and  draws  food-particles  into  the  gullet  by  the  vortex 
which  it  makes,  and  the  same  movements  draw  the  animal  through  the 
water. 

Draw  all  possible  shapes  of  this  minute  protozoan  and  make  notes  of 
its  peculiar  features.  It  is  well  illustrative  of  the  unity  of  Nature  that 
the  botanists  claim  Euglena  as  a  plant-cell. 

Expt.  8. — Brachionus. — This  little  animal  is  common  in  the  sand  at 
the  bottom  of  ponds  and  fish-containing  aquaria.  It  is  one  of  the  very 
curiously  shaped  class  of  Rotifers  (wheel-bearers).  It  is  a  multicell  of 
relatively  complex  organization,  having  an  alimentary  canal,  a  celomic 
cavity,  excretory  organs,  reproductive  glands,  a  nervous  system  including 
sense-organs,  and  muscles.     It  has  also  an  elaborate  body- wall. 

jNIake  out  the  trochal  disk  from  which  is  extended  in  front  the  long 
proboscis-like  organ  with  a  prehensile  arrangement  at  its  end.  See  the 
conspicuous  eye  of  red  pigment.  Study  the  telescopic  natiu-e  of  the  trunk 
and  especially  of  the  long  and  slender  "tail"  with  a  pair  of  nippers  at  its 
end  for  holding  fast  to  l)its  of  vegetal  debris  by  a  complex  muscular 
arrangement  of  claws.  The  tail  in  this  species  consists  of  four  or  five 
segments  completely  telescoping  when  the  animal  retracts.  Note  its 
inch-worm  mode  of  travelling. 

Another  rotifer,  Philodina,  inhabiting  our  aquaria  in  large  numbers, 
must  not  be  confused  with  Brachionus.  Its  trochal  disk  is  much  more 
conspicuous,  and  is  oftener  open. 


464 


APPEXDIX 


Expt.  9. — The  next  specimen  is  Tuhifex,  a  multicellular  round-worm 
livino;  everywhere  in  the  mud  at  the  bottom  of  ponds,  ditches,  etc. 
Easily  seen  with  the  naked  eyes,  use  objective  No.  3  to  study  the  often 


Fig.  256 


Daphnia  pulex,  De  Geer:  1,  antennules;  2,  left  antenna  (the  right  not  being  shown);  3,  man- 
dible; 5  to  9,  gill-feet;  6,  embryos  in  the  brood-sac;  g,  brain;  go,  optic  lobe  with  the  eye  above 
it;  h,  heart;  k,  e,  o,  various  stages  in  tlie  degeneration  of  the  aborted  eggs  into  food  within  the 
intestine.  The  long  spine  at  the  lower  dorsal  corner  is  a  means  of  defence  after  the  animal  has 
dived  into  the  silt  at  the  bottom.  The  curved  claw-like  projection  in  front  and  below  is  used 
for  removing  intruding  objects  from  without.      (Hertwig.) 

transparent  protoplasm  of  this  animal.  Note  especially  near  the  pos- 
terior end  a  large  slowly  pulsating  dorsal  artery — about  the  first  observed 
sign  of  a  heart  as  one"  looks  "upwanl"  in  the  animal  "series."     Make 


PROTOPLASM  AXD  SIMPLE  ANIMAL  FUXC'TIOXS 


4G5 


Fig.  2.57 


drawings  of  Tubifex,  if  possible,  showing  any  interesting  structures  to 
be  seen  in  the  animal. 

Expf.  10. — Cyclops  is  one  of  many  genera  of  the  Crustaceans  which 
inhabit  stagnant  waters  both  fresh  and  salt.  Note  the  general  shape  of 
the  animal,  and  his  antennae  in 
front  with  which  he  jumpingly 
swims  rapidly  through  the  water. 
Study  the  prominent  alimentary 
canal  (a  yellow  mass  in  the 
middle  line)  and  its  peristaltic 
surging  back  and  forth.  Note 
the  single  eye,  a  spot  of  pig- 
ment, above  and  in  front.  Note 
the  symmetrical  masses  of  eggs 
or  of  embryos  which  the  females 
carry  about,  one  mass  on  either 
side. 

Expt.  11. — Tardigrade  is  used 
as  a  type  of  the  animals  which 
survive  the  dried  and  hibernat- 
ing condition.  Two-day  demon- 
stration of  revival  after  drying. 
(See  Fig,  129  and  its  legend.) 

Daphnia  (Expts.  12  to  19). 
— The  last  of  the  microscopic 
animals  we  may  study  at  present 
is  Daphnia,  a  fresh-water  clado- 
ceran  crustacean  of  great  value 
and  interest  in  physiology  be- 
cause of  its  extreme  transpar- 
ency combined  with  a  relatively 
high  complexity  of  development. 
The  animal  is  to  be  studied  flat 
on  a  slide  with  water  too  small 
in  amount  to  allow  of  its  jump- 
ing about.  Note  (1 )  the  general 
striking  effect  of  movement  in 
every  part  of  the  animal  at  once; 
(2)  the  conspicuous  heart,  and 
the  blood-corpuscles  circulating 
over  the  body;  (3)  the  single  but 

compound  eye,  composed  of  omatidia  (single  eyes);  (4)  the  eye-muscles 
in  constant  action;  (5)  the  brain;  (6)  the  alimentary  canal  with  its 
surging  yellow-green  contents  and  its  movements  of  peristalsis;  (7) 
the  gill-feet;  (S)  the  brood-sack  and  its  probable  embryos  in  some  stage 
of  development  from  mere  eggs  to  forms  almost  like  their  mother;  (9) 
the  antenna?  with  which  it  jumps  in  a  characteristic  manner  through  the 
30 


Parts  of  Daphnia  pulex,  De  Geer:  a,  the  an- 
tennule  of  the  male;  b,  maxilla;  c,  the  first  "gill- 
foot"  of  the  female;  c',  the  same  of  the  male;  d, 
one  of  the  second  pair  of  gill-feet;  Br,  respiratory 
sac;  Ex,  exopodite.      (Glaus.) 


466  APPENDIX 

water,  etc.  Add  a  drop  of  methylene  blue  in  thin  mucilage  to  the  water 
close  to  the  animal. 

We  study  Daphnia  as  an  advance  ejntome  of  animal  functions,  and 
perhaps  nowhere  else  might  we  find  so  clearly  and  easily  displayed  so 
much  basal  physiology  for  the  mere  looking,  without  preparation  of  any 
sort.  We  may  readily  behold  in  little  Daphnia  the  fundamental  portions 
of  the  blood's  physical  composition  and  its  circulation,  respiration,  nutri- 
tion, the  nervous  system,  muscular  action,  and  reproduction  (especially 
embryology).  We  will  divide  our  observation  of  these  basal  activities 
orderly  as  follows : 

Expt.  12. — The  Blood  and  its  Circulation. — Careful  watching  of  the 
head-region,  especially  between  the  eye-muscles,  shows  clearly  even  with 
a  one-third  objective  the  many-shaped  one  sort  of  blood-corpuscles  of 
this  colorless  blood.  These  are  the  amehocytes  corresponding  to  the 
leukocytes  of  man,  but  doubtless  with  even  more  functions  to  perform. 
As  the  name  implies,  these  cells  have  ameboid  movements.  They  are 
relatively  few  in  number,  as  may  be  seen;  compare  the  10,000  to  the 
cubic  millimeter  present  in  man's  blood.  If  any  respiratory  pigment 
like  hemoglobin  exists  in  Daphnia's  blood  it  is  colorless.  Its  rate  of 
circulation  may  be  clearly  seen  by  means  of  the  corpuscles,  as  also  its 
general  course  about  the  wide  membrane-formed  smuses  under  the  shell. 
The  most  conspicuous  of  these  channels  lies  dorsad  to  the  alimentary 
canal  and  in  it  pulsates  the  heart.  Isolate  some  blood  and  examine  its 
corpuscles. 

Daphnia's  heart  (see  Dearborn,  Med.  Neivs,  ]\Iarch  21  and  28, 
1903  etc.),  is  as  simple  structurally  and  functionally  as  a  heart  well 
could  be.  It  consists  almost  wholly  of  two  series  of  smooth  muscle- 
cells  arranged  on  both  sides  of  the  dorso-ventral  plane  so  as  to  form  an 
ovate  saccule  open  in  front  and  with  an  ostium  (for  the  blood's  entrance) 
in  the  middle  of  each  side.  By  the  simultaneous  shortening  of  these 
blunt  fusiform  cells  the  heart  is  made  to  pulsate.  The  rate  usually  is 
about  240  per  minute,  but  it  varies  greatly  with  the  temperature.  The 
embryonic  rate  (see  the  brood-sac)  is  less  rather  than  greater  than  the 
adult  rate.  The  pulse-rate  persists  until  the  heart  entirely  stops,  and  is 
readily  variable  by  the  ordinary  physiological  salines.  Irritation  with  a 
fine  needle  in  the  abdominal  fold  stops  or  inhibits  the  pulsations  instantly. 
Study  the  cells  of  the  heart,  and  its  movements. 

Nicotine  in  2  per  cent,  aqueous  solution  gradually  slows  and  stops  the 
heart  in  diastole  after  several  minutes  of  great  irregularity.  Digitalis 
in  3  per  cent,  aqueous  solution  of  the  tincture  slows  and  invigorates  it, 
but  makes  it  irregular.  Curare  injected  into  circulation  stops  the  heart 
at  once.  Chloral  increases  the  power  and  the  length  of  the  diastole 
and  slows  the  pulse-rate.  Some  of  the.se  drugs  and  many  saline  in- 
fluences change  the  functional  size  of  the  heart  in  a  way  to  strongly 
suggest  the  presence  of  the  tonus  which  is  so  conspicuous,  for  example, 
in  the  turtle's  heart  and  probably  present  in  all  hearts — a  slow  tonal 
contraction  and  relaxation  beneath  the  pulsations.     The  existence  of  a 


PROTOPLASM   AND  SIMPLE  ANIMAL  FUNCTIONS  467 

two-phased  nerve-control  over  this  heart  is  at  least  exceedingly  prob- 
able. 

Expt.  13. — Respiration  is  carried  on  in  Daphnia  both  directly  by 
diffusion  through  the  thin  membranous,  chitinous  shell  and  by  means  of 
feathery  gills  attached  to  the  four  to  six  pairs  of  degenerate  legs  in  the 
ventral  middle  of  the  body,  when  seen  on  its  side.  The  former  means  is 
probably  much  the  more  important,  the  flatness  of  the  animal,  its  small 
size,  and  the  broad  exposure  of  blood  immediately  under  the  shell  making 
easy  the  direct  exchange  between  the  blood  and  the  surrounding  water. 
The  movements  of  the  gill-feet  are,  however,  probably  a  respiratory 
reflex  for  waving  the  gills  rapidly  through  the  water,  the  shell  being  open 
on  the  ventral  side.  Occasionally  the  abdominal  end  may  be  seen  to 
vigorously  extend  for  the  purpose  of  removing  particles  which  have 
entered  the  shell  and  are  interfering  with  the  feet's  free  activity.  Crush 
a  Daphnia  and  study  the  freed  gills  with  a  higher-power  objective. 

Expt.  14. — Nutrition  (including  the  preparation  of  food  for  the  me- 
tabolism of  the  tissues)  is  mechanically  a  simple  matter  in  Daphnia. 
Chemically,  however,  it  may  be  very  complex,  for  the  food  digested  is 
largely  proteid.  The  fine  hair-like  antennule  near  the  end  of  the  beak 
can  be  clearly  made  out,  but  whether  it  is  an  organ  of  taste,  smell,  or 
touch  is  not  known.  The  mouth-parts  are  not  easily  seen.  Observe 
the  conspicuous  quick  peristalsis  of  the  esophagus.  Note  the  digestive 
gland  at  the  summit  of  the  anterior  bend  of  the  greenish-yellow  gut  close 
to  the  brain;  this  probably  secretes  the  enzymes  which  dissolve  the  food. 
It  pulsates  as  a  continuation  of  the  peristaltic  waves  which  pass  up  the 
intestine.  Sop  a  speck  of  cotton  bearing  croton  oil  (poison)  on  the 
animal.  This  soon  causes  a  marked  increase  in  the  intestinal  movements. 
Observe  now  the  pulsations  of  the  digestive  gland.  The  peristalsis  of 
the  gut  is  an  antiperistalsis  and  now,  exaggerated  by  the  oil,  the  waves 
may  be  seen  to  start  at  or  near  the  anus  and  to  pass  in  a  typical  way  up 
the  gut  as  far  as  the  enlargement  opposite  the  heart,  but  here  a  less 
definite  surging  sort  of  movement  takes  the  place  of  the  true  peristalsis. 
Study  the  peristalsis  carefully,  measuring  the  speed  of  the  waves,  their 
frequency,  etc.  Within  ten  or  fifteen  minutes  after  administering  the 
croton  oil  the  entire  gut  is  usually  free  of  its  former  contents.  Note  the 
mode  of  defecation. 

Expt.  15. — Nervous  Function  and  the  Senses. — Note  the  brain,  the 
optic  lobe,  the  nerve  going  to  the  antennules,  the  trunk  extending  frora 
the  brain.  According  to  Lang,  there  is  a  ladder-like  ventral  cord  con- 
sisting of  seven  pairs  of  ganglia,  the  foremost  of  which  controls  the 
mandibles  and  maxillse,  and  the  remainder  the  six  pairs  of  legs. 

Demonstrate  the  presence  of  nerves  inhibiting  the  heart  by  a  light 
puncture  with  a  very  fine  bent  needle  over  the  caudal  bend  of  the  gut. 
The  heart  stops  instantly.  Oftentimes  in  a  few  minutes  it  begins  to  beat 
again  (as  does  the  mammalian  heart  after  stimulation  of  the  vagus). 

The  compound  eye  of  Daphnia  consists  of  five  simple  eyes  or  omatidia. 
The  ocular  muscles  should  be  studied  carefully  and  the  movements  which 


468  APPEXDIX 

they  give  the  eye.  These  movements  are  in  some  respects  Hke  those  of 
the  human  eye.  Note  the  nuclei  of  the  muscles,  and  the  thickening  of 
the  latter  as  they  contract. 

The  frontal  sense-organs  on  the  antennules  are  conspicuous  but  of 
unknown  function.  It  is  possible  that  the  antennae  bear  auditory  setae 
and  perhaps  touch-hairs. 

Expt.  16. — The  muscles  may  be  studied  in  both  their  aspects,  reflex 
and  voluntary.  The  heart,  gut,  and  eye  have  shown  us  examples  of  the 
former  sort.  The  first  joint  or  two  of  the  antennae  show  well  the  pulley- 
action  of  the  voluntary  muscles  in  operating  the  limbs. 

Expt.  VJ .—Emhryolociy. — In  many  specimens  may  be  seen  dark-brown 
cases  containing  two  eggs  each,  which  are  intended  to  persist  when  all  the 
adults  have  died  either  of  ice  or  of  drying.  These  are  the  "  winter  eggs." 
In  other  females  there  are  from  three  to  eleven  embryos  crowded  in  the 
brood-sac  above  the  alimentary  canal.  These  may  be  found  of  every 
age  from  the  mulberry  stage  up  to  the  fully  formed  young  daphnias  ready 
to  break  out  of  the  sac.  The  brood-sac  contains  an  albuminous  fluid 
which  nourishes  the  young.  The  eggs  begin  in  groups  of  four,  and  part 
of  these  break  down  to  nourish  the  remainder. 

The  ovaries  and  testes  are  simple  paired  tubes;  the  sexes  are  distinct 
and  males  are  relatively  uncommon. 

Expt.  18. — Drug-actions  and  similar  eft'ects  might  be  studied  largely 
on  Daphnia  with  benefit,  for  here  their  action  on  brain,  heart,  respira- 
tion, and  digestion  might  be  actually  observed  directly  in  its  details. 

Expt.  19. — Finally,  allow  the  animal  to  dry  up  on  the  slide.  Observe 
thus  the  relative  persistence  of  the  organs,  and  also  the  optical  changes 
which  protoplasm  undergoes  when  its  water  is  decreased. 

Besides  the  genera  mentioned  above,  the  following  sliould  usually  be 
found  in  abundance  in  the  varied  aquaria  of  the  I^aboratory :  Stylonychia, 
Hydra,  Amphileptus,  Philodina,  and  Chetonotus. 


II,  CILIARY  MOTION. 

Expt.  20. — Direction  and  Speed  of  Movement  Produced. —  (Apparatus: 
Frog-board,  small  cork  platform,  lead  weights  (0.5  to  5  gm.),  watch,  hot 
normal  saline,  metric  rule.)  Pith  the  frog's  brain  (see  Expt.  35)  and 
fasten  the  animal  well  stretched  out  on  its  back  to  the  frog-board.  Divide 
the  lower  jaw  longitudinally  on  the  median  line  and  extend  the  incision 
through  the  esophagus.  Turn  the  flaps  widely  back  and  fasten  them 
with  clips.  Place  the  little  cork  block  on  the  mucous  membrane  of  the 
roof  of  the  mouth  between  the  eyes.  {A)  Measure  witli  watch  and  rule 
the  speed  at  winch  it  is  carried  downward  in  millitneters  per  minute. 
{B)  Load  the  cork  with  weights  and  determine  the  limit  of  load  in  grams. 
(C)  Warm  the  membrane  with  hot  (60°)  normal  saline  solution  (NaCl) 
anrl  compare  the  two  speeds.     Make  ten  measurements  and  average 


NOTES  OX  SOME  OF  THE  APPARATUS  469 

them.  Subtract  al<;el)raically  this  average  from  each  measurement. 
(Place  all  the  arithmetical  work  in  the  note-books.)  Use  the  same  method 
in  comparing  the  speed  on  the  warmed  mucosa,  and  state  the  acceleration 
in  percentage  of  the  cold  rate. 

Note  (1)  the  direction,  (2)  the  speed,  and  (3)  the  great  power  of  the 
ciliary  motion  (Bowditch). 

Expt.  21. — Cocrdl nation  of  Cellular  Movemeid. —  (Apparatus:  Frog- 
board,  powdered  charcoal,  hot  wire.)  With  the  heated  wire  superficially 
cauterize  a  spot  of  the  ciliated  mucous  membrane  which  has  been  lightly 
powdered  with  charcoal.  Observe  carefully  where  there  is  movement 
.still  and  where  it  is  not.  It  will  be  found  that  the  motion  is  stopped  not 
only  on  the  burned  spot,  but  throughout  a  small  isosceles  triangle  whose 
apex  is  at  the  spot  and  whose  base  is  toward  the  esophagus. 

]\Iost  of  the  infusoria  we  have  been  studying  move  by  means  of  cilia; 
so  do  spermatozoa.  Ciliated  epithelium  lines  the  human  air-passages, 
the  Fallopian  tubes,  the  cerebral  ventricles,  the  ventricle  of  the  cord, 
the  Eustachian  tube,  the  vasa  efferentia,  etc.  Its  general  function  is  to 
move  a  liquid  or  small  particles  over  a  surface  or  through  a  tube.  Nerves 
•are  probably  nowise  concerned. 

The  cause  of  the  movement  of  cilia  lies  in  the  body  of  the  cell  from 
which  they  extend,  for  they  have  no  power  of  movement  when  separated 
from  their  cells;  probably  the  nucleus  exerts  the  control  in  some  way. 
Cilia  have  a  rhythm  which  is  broken  only  by  external  influences  or  when 
the  cell  is  about  to  rest.  Another  conspicuous  quality  of  the  movement 
of  cilia  is  the  progression  of  the  bending  movement  from  one  cilium  to 
the  next,  each  phase  being  represented  by  many  different  cilia  at  the  same 
time;  different  rows  of  cells  are  coordinated  in  this  rhythm. 

The  active  or  contractile  movement  of  the  cilia  is  probably  the  erecting 
phase  and  not  the  phase  in  which  it  Ijends  downward,  for  this  latter  corre- 
sponds to  relaxation.  The  contractile  phase  is  quicker  than  the  other; 
contraction  of  the  side  of  the  cilium  convex  in  its  resting  position  pulls 
the  cilium  to  a  vertical  position.  Reversal  of  the  movement  is  sometimes 
observed,  but  never,  so  far,  in  vertebrates.  (Consult  the  literature  in 
the  libraries,  especially  Verworn). 


III.   NOTES  ON  SOME   OF  THE   APPARATUS. 

Review  discussion  of  electrical  physics  and  demonstration  of  the  galvanic 
cell,  the  inductorium,  the  rheocord,  the  chronograph,  Pohl's  commutator, 
the  muscle-lever,  the  electro-magnetic  signal,  the  non-polarizable 
electrode,  the  capillary  electrometer,  the  tuning-fork,  etc. 

However  much  a  student  may  know  about  physics  (and  it  is 
almost  always  far  too  litde),  it  is  necessary  to  learn  the  theory  and 
practice  of  the  simple  apparatus  used  in  experimental  physiology,  else 
much  time  and  material  will  be  wasted.  In  this  work  several  matters 
respecting  electrical  apparatus  are  essential  which  elsewhere  often  are 


470  APPENDIX 

unimportant — for  example,  the  direction  of  the  current  and  the  relations 
of  the  ions  bearing  it.  The  more  physics  the  student  knows,  the  better 
will  he  grasp  physiology,  which  is  largely  organic  physics  and  chemistry. 

Didactic  Rules  for  Using  the  Electrical  Apparatus,  etc. — Dry-cell. — 
This  is  a  modified  Leclanche  battery-element,  the  electricity  being 
generated  by  the  action  of  salammoniac  on  the  zinc  plate  and  conducted 
inward  to  the  carbon  plate  by  hydrogen  and  ammonia  anions.  Hence 
the  carbon,  the  negative  plate,  is  the  positive  pole  of  the  cell,  and  in  a 
conductor  completing  the  circuit  outside  the  cell  the  current  passes  from 
the  carbon  (anode)  to  the  zinc  (cathode).  This  is  an  open-circuit  cell 
and  its  poles  must  never  for  a  minute  be  left  connected  by  a  conductor 
when  not  in  use.  Each  cell  has  a  pressure  of  more  than  one  volt. 
Always  remove  the  wire  from  one  of  its  poles  when  its  use  is  finished  for 
the  day. 

The  Inductorium  or  Induction-coil. — ^The  strength  of  the  momentary 
currents  induced  in  the  secondary  coil  depend  on  (^4)  the  strength  of  the 
battery-make  and  -break;  {B)  on  the  closeness  of  the  two  coils  to  each 
other;  and  (C)  on  the  angle  between  the  rings  of  wire  of  the  two  coils 
(this  angle  determining  the  number  of  the  inducing  lines  of  force).  The 
instrument  is  used  in  three  sorts  of  ways :  (1)  to  give  single  make  induction- 
shocks;  (2)  to  give  single  break  induction-shocks;  and  (3)  to  produce 
a  current  of  alternating  induced  electricity,  each  double  vibration  of  the 
automatic  armature  producing  two  alterations  of  this  current.  To  pro- 
duce single  make  or  break  shocks  the  left-hand  binding-post  and  the 
middle  binding-post  are  attached  to  the  battery  wires,  the  short-circuiting 
key  left  open,  and  the  battery-current  made  and  broken  with  the  simple 
key.  The  break  induction-shock  is  stronger  than  the  make  induction- 
shock  (because  of  the  absence  of  the  conflicting  extra-currents  in  the 
primary  coil  at  the  break).  To  produce  (3)  the  alternating  current,  the 
right  and  left  corner  binding-posts  are  employed.  Stimulation  is  applied 
by  opening  the  previously  closed  short-circuiting-key  on  the  secondary 
coil  while  the  simple  key  in  the  primary  or  battery  circuit  is  held  closed. 
The  short-circuiting  key  must  be  kept  closed  except  while  using  the 
alternating  current  in  order  to  avoid  explosive  tension  at  the  secondary 
electrodes.  Never  bend  in  any  way  the  vibrating  filament  of  the  hammer- 
armature:  ask  the  instructors  to  make  any  adjustments  which  may  occa- 
sionally be  necessary. 

When,  as  is  customary,  it  is  desired  to  stimulate  with  a  make-shock  or 
with  a  break-shock  only,  the  other  in  either  case  must  be  carefully  kept 
from  stimulating,  for  else  two  contractions  instead  of  one  woukl  be 
occasioned.  To  do  this,  use  the  short-circuiting  key  on  the  secondary 
coil  in  the  appropriate  way.  To  use  a  make-shock  only:  Close  the  simple 
key  in  the  circuit  (the  short-circuiting  key  being  open);  this  does  the 
stimulating.  Hold  down  the  simple  key  and  close  meanwhile  the  short- 
circuiting  key;  then  release  the  simple  key.  To  use  a  break-shock  only: 
Close  the  short-circuiting  key;  close  the  simple  key  in  the  circuit  and 
hold  it  dfnvn.     ()]>('])  the  sliort-circuiting  key;  then  on  releasing  the  simple 


NOTES  ON  SOME  OF  THE  APPARATUS  471 

key  the  muscle  is  stimulated  by  a  break-shock  only.  This  is  called 
"cutting  out"  the  shock  not  desired. 

The  common  error  at  first  is  having  pressed  down  the  simple  key  to 
at  once  release  it,  forgetful  that  this  gives  two  shocks  instead  of  one. 
The  simple  key  must  always  be  held  down  (closed)  until  the  desired 
reaction  has  completed  itself;  then  the  break-shock  will  do  little  harm  save 
toward  wearying  the  muscle  or  other  material. 

The  rhythmic  chronograph  consists  of  a  flat  steel  spring  (vibrating 
at  any  one  of  many  rates  per  second  and  breaking  the  circuit  at  each 
double  vibration)  actuating  the  electromagnetic  signal.  Used  in  one 
way  it  breaks  the  signal-circuit  once  a  second  (caution  as  to  the  eyes). 
Used  the  other  way  (horizontally)  it  actuates  the  signal  either  fifty  times 
per  second,  ten  times  per  second  as  desired,  or  at  any  other  rate  near 
these. 

The  non-polarizable  electrodes  must  be  used  especially  in  experiments 
on  nerves  whenever  delicate  quantitative  work  is  undertaken.  These 
prevent  disturbance  of  the  ions  of  the  tissues  by  the  chemical  action  be- 
tween their  salines  and  the  metal  of  wires,  etc.  The  porcelain  boot- 
electrode  is  most  convenient  when  the  moist-chamber  is  used,  and  the 
camel's-hair  brush  form  at  other  times.  In  either  form  no  metal  is 
in  contact  with  the  tissue,  the  electricity  being  conducted  by  Ringer's 
fluid  in  the  boot  or  the  brush. 

The  capillary  electrometer  (A)  measures  very  delicate  electric  currents 
and  (B)  shows  their  direction.  It  is  in  general  only  in  research-work 
that  we  care  to  know  the  exact  values  of  these  electric  currents,  for  they 
are  not  known  to  be  physiological ;  but  their  direction  is  of  more  importance. 
The  movement  of  the  end  of  the  column  of  mercury  in  the  capillary  tube 
is  in  the  direction  of  the  current,  the  surface-tension,  usually  holding  it 
still,  being  then  lessened  or  else  increased  as  the  case  may  be.  If  the 
current  be  down  the  tube,  the  tension  is  lessened;  if  up,  it  is  increased. 
A  form  with  the  capillary  large  enough  to  be  seen  readily  without  a  lens 
is  often  a  convenience  and  fully  precise  enough  for  class-work  purposes 
in  schools  with  the  present  too-short  course  of  four  years. 

Pohl's  commutator  or  pole-changer  is  used  in  three  ways :  (-.4)  To  change 
the  direction  of  a  current.  The  cross-wires  then  are  in  place,  the  battery- 
wires  (afferent)  attached  to  the  posts  of  the  rocker,  and  the  efferent 
or  stimulating  wires  attached  to  the  pair  of  posts  on  one  side  or  other  of 
the  rocker.  (B)  To  shift  a  battery-current  into  either  of  two  efferent 
currents  at  will,  the  cross-wires  are  removed  and  the  battery-wires  fastened 
in  the  two  pairs  of  posts  ("rocker-posts")  remaining.  (C)  As  a  simple 
key,  the  cross-wires  are  removed  and  the  wires  of  the  circuit  concerned 
are  placed  one  in  a  rocker-post  and  the  other  in  a  post  adjacent  to  it. 

The  rheocord  is  used  to  subdivide  a  weak  current  so  that  a  w^hole  or 
any  fraction  of  it  may  be  employed;  also  for  gradually  increasing  or 
decreasing  the  strength  of  a  weak  current  used  as  a  stimulus.  In  order 
to  reduce  the  strength  of  a  current,  place  the  two  wires  carrying  the 
current  from  the  dry-cell  in  the  two  corner  binding-posts,  and  attach 


472  APPEXDIX 

one  of  the  efferent  wires  also  to  one  of  these  posts,  and  the  other  in  the 
post  to  which  the  movable  block  is  hitched.  Then  when  the  block  is  at 
the  post  containing  two  wires  none  of  the  incoming  current  is  taken  off 
to  the  nerve  or  muscle;  when  the  block  is  half-way  do\Mi  the  german- 
silver  wire  half  the  current  passes  out,  and  when  at  the  opposite  corner 
post  all  of  it.  To  increase  or  decrease  the  current  gradually,  merely 
slide  the  block  along  the  german-silver  wire  in  the  direction  required. 
(See  Expt.  44.) 

The  electromayneiic  signal  is  always  placed  in  the  primary  or  battery- 
circuit  and  cannot  be  actuated  by  the  induction-current.  It  should 
\^Tite  immediately  beneath  the  myograph  pen. 

The  tuning-fork  makes  one-hundred  double  vibrations  per  second 
and  vibrates  fifteen  or  twenty  seconds  at  a  time.  It  is  to  be  held  in  the 
hand  and  set  in  action  by  pinching  together  the  bars  and  releasing  them 
suddenly.     The  T\Titing  pen  is  attached  to  the  edge  of  the  end  of  one  bar. 

The  kymograph  or  movement-recorder  has  several  speeds.  By  means 
of  the  screw  on  top  of  the  drum-spindle  the  drum  can  he  raised  off  the 
friction-bearing  and  may  then  be  spun  by  hand  independently  of  the 
clock-work.  Keep  the  kymograph  well  w^ound  up  in  order  to  obtain 
approximate  constancy  of  speed.  The  \mting-pen  should  always  be 
at  a  tangent  to  the  surface  of  the  drum,  which  must  go  in  the  right  direc- 
tion in  reference  to  the  tinsel  pen  and  never  so  as  to  tend  to  double  it  up. 
In  other  w^ords,  have  the  kymograph  always  to  the  left  of  the  remainder 
of  the  apparatus. 


IV.  THE  MECHANICS  OF  THE  CIRCULATION. 

Expt.  22  consists  of  a  demonstration  of  the  various  parts  of  the 
circulation-scliema,  what  they  correspond  to  in  the  animal,  and  how  to 
use  the  apparatus  in  the  laboratory. 

Fig.  258 


Brachial  sphygmogram.-.      Made  on  the  brachial  artery  with  the  simple  laboratory  thistle- 
tube  sphygmograph.      To  be  read  from  left  to  right.      Time-line  is  in  seconds. 

The  bulb,  representing  the  ventricles,  must  always  be  compressed  in 
the  palm  of  the  hand  at  the  rate  at  which  the  human  heart  works,  using 
a  watch  or  the  actual  pulse  as  a  guide  to  the  correct  rate.  (A  newer 
form  of  the  circuhition  .schema  on  the  market  has  no  bulb,  but  an  excen- 
tric  crank-mechanism  in  its  place.  The  valves  furthermore  can  be 
more  readily  changed,  making  it  preferable.)  The  valve-flaps  should 
be  of  thin  rubber  (lam.     The  capillary  resistance  must  be  so  arranged 


THE  MECHANICS  OF  THE  CIRCULATION  473 

(by  means  of  the  compression-clamp)  that  the  pressnre  in  the  arterial 
manometer  is  high.  Under  these  conditions  observe  (1)  that  the  outflow 
into  the  bowl  is  constant.  This  condition  (representing  the  constancy 
of  the  capillary  flow)  is  due  to  two  factors  present  in  the  circulation:  the 
great  elasticity  of  the  arteries  and  the  high  resistance  in  the  capillaries. 
If  either  of  these  be  lessened  the  flow  is  no  longer  constant,  but  inter- 
mittent with  each  beat  of  the  heart.  Thus,  with  extremely  relaxed 
capillaries  one  sometimes  observes  a  venous  pulse.  Note  (2)  the  high 
and  relatively  constant  pressure  in  the  arteries,  and  (3)  the  very  low 
pressure  in  the  veins. 

Expt.  23. — The  normal  sphygmogram  is  the  pulse-record  made  with  a 
sphygmograph  ("pulse-writer")  on  the  kymograph-drum  covered  with 
smoked  paper.  Demonstration  of  the  important  graphic  method,  and 
of  the  sphygmograph.  Fasten  the  glazed  paper  to  the  drum  so  that  the 
margins  beyond  the  latter  at  both  ends  shall  be  the  same.  The  layer 
of  soot  need  not  be  black,  but  it  should  be  fairly  uniform.     Cut  ofl:'  the 

Fig.  259 


0 

A  simple  myogram  to  show  the  deformation  of  the  curve  by  tlie  use  of  arc-levers  and  the 
mode  of  correcting  the  error.  Each  point  of  the  curve  save  o  is  too  far  toward  the  right,  but 
can  be  put  in  its  proper  place  by  setting  it  to  the  left  its  respective  distance  as  shown  in  the 
angle  o.  o,  a,  b,  x.  (Weiss.)  In  practice  the  error  is  lessened  by  having  the  lever's  pivot  opposite 
the  middle  of  the  curve  instead  of  opposite  its  bottom. 

margins  and  never  re-smoke  the  paper  after  this  has  been  done.  Keep 
the  kymograph  wound  up.  Use  a  speed  of  the  drum  which  will  make 
a  sphygmogram  one-half  as  long  again  as  it  is  high.  After  applying 
the  receiving  tambour  to  the  artificial  artery,  open  the  pinchcock  to 
equalize  the  pressure  within  the  sphygmograph.  Insert  one  or  more 
wooden  strips  beneath  the  "artery"  if  necessary  to  obtain  a  good  record. 
The  tinsel  writing-pen  should  be  at  least  two  centimeters  long  on  the  end 
of  a  straw  lever  about  15  centimeters  in  length.  The  whole  lever  should 
be  always  held  at  a  tangent  to  the  cylinder's  surface. 

It  is  fundamentally  important  that  each  of  the  conditions  should  be 
normal  except  the  one  studied  in  each  case.  Thus  the  pulse-rate,  the 
capillary  resistance,  the  leverage,  the  drum-speed,  etc.,  all  must  be 
exactly  as  in  making  the  norm  with  which  the  abnormal  sphygmograms 
are  to  be  compared.  A  normal  curve  must,  then,  accompany  each 
pathological  curve.  This  singleness  of  variation  is  of  course  one  of 
the  basal  principles  governing  all  biological  research,  as  Francis  Bacon 
and  ]Mill  long  ago  pointed  out. 


474  APPEXDIX 

Now,  having  everything  ready,  make  a  series  of  (1)  normal  sphygmo- 
grams  around  the  drum  (pulse-rate  of  75,  high  capillary  resistance). 
Analyze  the  curve.  Observe  (A)  the  speed  of  the  uprise  of  the  writing- 
lever;  (J5)  the  speed  of  its  downfall;  (C)  the  dicrotic  notch.  (2)  Make 
a  series  of  sphygmograms  with  a  low  capillary  resistance  and  compare^ 
in  whole  and  in  part,  with  the  normal  curve.  (3)  Make  a  series  with 
a  pulse-rate  lower  than  75.  INIake  these  three  sets  of  sphygmograms 
directly  under  each  other  so  that  they  may  be  the  better  compared,  the 
drum-speed  being  constant.  Note  the  characteristics  of  each,  and 
study  out  exactly  what  each  means  in  the  body. 

The  pathological  sphygmogram  records  abnormalities  in  the  cardiac 
valves:  stenosis  and  incompetency  of  both  the  auriculo-ventricular  and 
the  aortic  valves.  These  make  up  the  four  common  valvular  heart- 
lesions  found  in  man. 

Expt.  24. — Incompetency  of  the  Auriculo-ventricular  or  Mitral  Valve. — 
To  imitate  this  condition  in  the  schema,  carefully  draw  out  the  left- 
hand  valve-tube  and  turn  the  thin  rubber  covering  so  that  it  no  longer 
protects  the  hole  in  the  glass  from  regurgitation  of  the  "blood."     Re- 

FiG.  260 


Normal  sphygmogram  made  on  the  artificial  circulation-apparatus.  The  capillary  resistance 
and  the  blood-pressure  both  were  high.      To  be  read  from  left  to  right.      Time-line  is  in  seconds. 

place  and  make  a  series  of  sphymograms  at  the  normal  rate,  and  com- 
pare with  the  normal  curve.  Note  that  the  curve  is  different  from  the 
normal,  V^ecause  much  of  the  "blood"  now  regurgitates  from  the  ventricle 
into  the  auricle  at  each  beat.  The  shape  of  the  curve  may  not  be  much 
different  from  the  normal,  but  the  tracing  is  narrower  vertically.  Re- 
place the  rubber  on  the  valve-tube  in  its  normal  place  (Fig.  261). 

Expt.  25. — Aortic  incompetency  is  produced  similarly  on  the  other 
valve.  Make  a  series  of  curves  and  study  their  abnormal  characteristics. 
Note  the  low  pressure  in  the  arteries  and  its  great  variation ;  tliese  make 
a  soft  and  bounding  "gaseous"  pulse.  Replace  the  valve-dam  in  nor- 
mal position. 

Expt.  26. — Mitral  stenosis  is  produced  by  removing  the  valve-tube 
and  loosely  tying  a  thread  over  its  orifice  so  that  less  "blood"  than 
normally  may  pass  through.  Be  careful  not  to  tie  the  thread  too  tightly. 
Make  a  series  of  sphygmograms  and  compare  them  with  norm.  Observe 
the  shape  of  the  curve.     Restore  the  schema  to  its  normal  condition. 

Expt.  27. — Aortic  steno.'sis  is  produced  similarly  on  the  aortic  valve. 
Make  a  series  of  curves  and    compare  them  with  the  normal  sphyg- 


THE  MECHANICS  OF  THE  CIRCULATION 


475 


mogram.  Replace  the  valves  in  their  normal  position  and  wipe  the 
whole  instrument  dry. 

What  are  the  characteristics  of  each  sort  of  abnormal  sphygmogram  ? 
Give  the  hydraulics  of  each  case.     Important. 

Expi.  28. — Speed  of  the  Pulse-wave  in  Man. — (Apparatus:  Two 
thistle-tube  sphygmographs,  tubing,  kymograph,  tuning-fork,  adjust- 
able stand-rod,  clamps,  two  chairs,  rule,  a  tall,  thin  man  with  strong 
pulse.)  Let  the  subject  sit  sidewise  in  one  chair  at  the  table  with  his 
bared  right  foot  on  its  outer  side  in  the  other  chair  in  front  of  him,  and 
his  head  resting  on  a  folded  towel  on  the  table,  left  ear  down.  By  means 
of  a  stand-rod  and  clamps  adjust  the  sphygmograph  with  the  shorter 


A^ ^. 


Fig.  261 


yi__yi A. 


Abnormal  sphygmograms  made  on  the  artificial  circulation-apparatus.  The  top  line  repre- 
sents mitral  stenosis;  the  line  next  below,  mitral  regurgitation;  the  next  line,  aortic  stenosis;  and 
the  bottom  line,  aortic  regurgitation.      To  be  read  from  left  to  right.      The  time-line  is  in  seconds. 

tube  to  the  subject's  right  carotid  artery.  By  means  of  a  table-clamp,  etc., 
adjust  the  transmitting  tambour  of  the  long-tubed  sphygmograph  to 
the  posterior  tibial  artery  of  the  right  foot  at  a  point  about  half-way 
between  the  middle  of  the  inner  malleolus  and  the  middle  of  the  bottom 
of  the  heel,  the  foot  being  naked.  Both  sphygmographs  must  be  firmly 
held  by  clamps  and  the  foot  in  a  firm  position. 

Adjust  the  recording  tambours  one  close  above  the  other  on  the  kymo- 
graph-drum with  their  writing-points  exactly  in  a  vertical  line.  Spin  the 
drum.  Apply  the  100  d.  v.  tuning-fork.  Count  the  hundredths  of  a 
second  between  the  uprise  of  the  two  levers  in  several  cases.  This 
obviously  is  the  average  time  required  for  the  pulse-wave  to  travel  from 


476  APPENDIX 

the  left  ventricle  to  the  foot  less  the  time  required  for  its  passage  from 
the  ventricle  up  the  carotid.  Measure  as  nearly  as  possible  these  two 
distances.  Calculate  the  pulse-wave  speed  from  these  data  in  meters 
per  second. 

Compare  this  result  with  the  blood's  speed. 

Expt.  29. — Demonstration  of  the  Actual  Circulation  in  the  Frog's  Foot. 
■ — (Apparatus:  Compound  microscope,  stand-rod,  clamp,  two  long,  wide 
slides,  wax,  small  clips,  green  frog,  cloth,  tea-lead.)  Pith  the  frog's 
brain  and  wrap  the  animal  excepting  one  foot  rather  tightly  in  the  cloth 
and  tea-lead  previously  wet  in  water.  Support  the  frog  and  stretch  out 
his  exposed  foot  over  the  two  slides  placed  one  over  the  other  and  held 
in  the  cork-lined  clamp  just  over  the  microscope's  stage.  Secure  an 
outer  toe  in  each  of  the  clips  and  separate  the  clamped  slides  until  the 
web  of  the  foot  is  stretched  over  the  opening  in  the  stage,  catching  the 


Diagrammatic   section   of   the   alveolar  wall   of   a  frog's   lung:    o,  a,  capillary   spaces; 
h,  epithelial  cells;   c,  muscle-fibers  in  the  alveolar  partitions.      (F.  E.  Schulze.) 

clips  on  the  outer  edges  of  the  slides.  Use  a  2-inch  objective  to  find  the 
best  spot  where  the  web  is  flat  and  level,  the  circulation  lively,  and  the 
web  free  of  pigment-cells  if  possible.  Study  with  the  No.  3  objective. 
(See  also  page  304.) 

Observe  how  the  speed  and  redness  of  the  blood  are  proportional  to 
the  diameter  of  the  vessel.  See  the  shape  and  multitude  of  the  erythro- 
cytes and  the  shape  and  fewness  of  the  (smaller)  leukocytes.  (Com- 
pare the  red  corpuscles  with  those  of  man.)  Note  the  constancy  of  the 
flow,  at  least  after  the  shock  of  the  pithing  has  passed  off. 

Such  a  preparation  is  often  good  for  two  days. 

The  phenomena  of  inflammation  may  be  studied  by  applying  a  weak 
solution  of  mustard  oil  or  of  croton  oil  to  the  web.  The  action  of  adrena- 
lin also  should  be  o})served — a  drop  of  0.01  per  cent,  saline  solution 
being  applied. 

V.  RESPIRATION. 

Expt.  30. — The  Pneumatics  of  External  Respiration. — (x\pparatus: 
the  schema  of  the  respiration.)  A.  Normal  Breathing. — Lower  the 
fliaphragm  rhyUimically  and  note  how  the  finger-cot  lung  fills  with  air 
falling  into  it  through  the  open  glottis.  Observe  the  slight  changes  of 
jH-essure  in  the  two  manometers.     What  is  it  that  expands  the  lung? 

B.  Asphyxia. — Push  the  glass  plug  into  the  glottis,  thus  closing  the 
respiratory  opening  to  the  exterior.     Now  the  lung  no  longer  fills  as  the 


RESPIRATION 


477 


Fig.  263 


diaphragm  slightly  descends,  for  the  falling-in  of  air  is  impossible.  Note 
the  great  changes  of  pressure  as  shown  in  the  manometer  in  connection 
with  the  pleural  cavity. 

C.  Pneumothorax. — Pull  out  the  glass  plug  which  closes  the  tube 
connected  with  the  pleural  cavity.     The  diaphragm  now  descends  with 
great  freedom,  but  no  air  falls  int(^  the  lung  because  no  distending  suction 
outward  is  exerted  on  the  lung- walls.     The 
weight  of  the  atmosphere  is  equalled  by  that 
of  the  air  outside  the  lung  in  the  pleural 
cavity. 

Expt.  31. — Respiration  in  the  Frog. —  (Ob- 
servation only. )  The  frog  has  no  diaphragm, 
but  makes  the  muscles  of  the  floor  of  his 
large  mouth-cavity  serve  the  same  purpose, 
with  the  important  difference  that  whereas 
the  descent  of  the  diaphragm  in  birds  and 
mammals  sucks  the  air  into  the  lungs,  here 
the  mouth-floor  muscles  push  it  in  with  a 
true  bellows-like  movement. 

Observe  the  rhythmic  movements  of  these 
muscles;  the  rhythm  is  easily  disturbed  by 
handling,  etc.,  but  not  stopped  long  while 
the  animal  is  in  the  air.  While  submerged 
in  the  water  the  frog  gets  oxygen  only 
through  its  skin.  Note  the  closure  of  the 
nostrils  at  each  inspiration.  They  are 
the  automatic  valves  of  these  inspiratory 
bellows,  opening  to  admit  the  air  and  closing 
promptly  to  prevent  its  return,  thus  forcing 
it  to  enter  the  lungs,  the  glottis  opening  as 
the  nostrils  close. 

Expiration  is  here  more  of  an  active  pro- 
cess than  in  mammals;  the  muscles  along 
the  sides  of  the  body-cavity  compress  the 
viscera  and  so  the  lungs,  the  air  passing  out 
in  a  quick  spurt  through  the  opened  nares. 

Expt.  32. —  The  Breath-rate  of  Anolis. 
The  Normal  Stethogram. —  (See  Chapter 
on  Respiration.)  (Apparatus :  Anolis  stetho- 
graph,  and  kymograph.)  Adjust  the  stetho- 
graph    for    writing    on    the   smoked    drum 

by  means  of  the  aluminum  heart-lever.  Fasten  the  lizard  (Florida 
"chameleon")  on  the  board  so  as  to  be  immovable  but  uninjured  in 
any  way,  strapping  down  firmly  the  tail  and,  if  necessary,  the  head. 
Adjust  the  animal  within  the  stethograph  so  that  the  latter's  levers  press 
evenly  on  either  side  of  the  body  where  the  respiratory  movement  is 
greatest,  close  to  the  forelegs.      Warm   the  animal   up   somewhat  if 


Lungs  of  the  chameleon  (Cha- 
meleo  vulgaris).  (Wiedersheim.) 
Observe  their  relatively  great  size 
and  their  simple  sacculation. 


478 


APPENDIX 


necessary.     With    the    watch   count    the   number   of   respirations   per 
minute. 

By  analysis  of  the  meaning  of  the  different  parts  of  the  pneumogram 
note  the  characteristics  of  the  respiratory  process  in  this  animal.    Observe 


Fig.  264 


The  AnoHs  stethogram.  A  slightly  apneic  type  of  the  breath-movements  of  Anolis.  Observe 
the  slight  pause  after  inspiration,  but  that  there  is  none  between  expiration  and  thenext  inspi- 
ration.     To^^be  read  from  right  to  left.      Original  size.      The  time-line  is  in  seconds. 

(A)  that  there  is  no  pause  between  expiration  and  the  succeeding  in- 
spiration; (B)  that  there  is  a  slight  pause  between  inspiration  and  expira- 
tion ;^(C)  that  the  inspiratory  movement  is  a  strong,  quick,  active  mus- 

FiG.  265 


Apparatus  (Anolis  stethograpli,  etc.)  as  set  up  by  students  to  study  the  respiration  of  the 

.southern  "chameleon." 

cular  movement;  (D)  that  the  expiratory  curve  (the  down  stroke  of  the 
pen)  is  apt  to  l)e  broken  by  a  pause  at  some  part  of  the  descent,  usually 
either  a  shght  stay  soon  after  the  expiration  begins  or  a  much  larger 
one  about  half-way  through  it.     This  expiration  is  characteristic  of  a 


RESPIRATION 


479 


^passive  movement  easily  obstructed,  and  of  the  breathing  of  lizards 
generally. 

Expt.  33. — Apnea. — (Apparatus:  Anolis  stetliograph  and  kymograph.) 
Place  the  animal  as  in  the  last  experiment  and  make  a  normal  pneumo- 


FiG.  266 


The  Anolis  stethogram.  This  shows  the  inspiratory  apnea  (so  marked  a  characteristic  in  the 
respiration  of  many  lizards)  occurring  during  rapid  rhythmic  breathing.  To  be  read  from  right 
to  left.      Original  size.      The  time-line  is  in  seconds.      (April,  1900.) 

gram.  Stimulate  him  by  tapping  his  nose  very  gently  with  a  straw. 
He  will  stop  breathing  for  a  time  and  after  a  full  inspiration.  Note 
the  number  of  breaths  covered  by  this  pause  and  the  increased  depth 
and  frequency  of  the  respirations  following  it. 

Fig.  267 


+  -I-1-4-U4-J-U 


The  Anolis  stethogram.  This  shows  the  strongly  apneic  type  of  the  breathing  of  the  southern 
"chameleon."  Observe  that  the  inspiratory  movements  are  never  interrupted.  To  be  read  from 
right  to  left.      Reduced.      The  time-line  is  in  seconds. 

Expt.  34. — Anesthesia. — (Apparatus:  Anolis  stethograph,  kymograph, 
small  wads  of  filter  paper  soaked  in  chloroform.)  i\\i\\e  the  animal  is 
recording  a  normal  pneumogram,  place  near  its  nostrils  the  wad  of  filter- 


480  APPENDIX 

paper  soaked  in  chloroform.  Note  the  primary  stimulating  stage  (in 
which  the  animal  struggles),  with  the  acceleration  and  deepening  of  the 
respirations,  followed  soon  by  the  second  stage,  in  which  the  respirations 
become  slower  and  shallower.  The  anesthetic  should  be  removed  at 
this  time  lest  the  animal  be  killed  by  cardiac  paralysis.  Note  the  gradual 
return  to  the  normal  respiration. 

In  the  remainder  of  the  experiments  frog-life  may  often  be  economized 
greatly  by  arranging  the  order  in  wiiich  the  experiments  are  performed 
at  each  laboratory-period.  The  order  matters  little  theoretically. 
Experiments  not  requiring  extensive  cutting  should  be  done  before  those 
demanding  it,  therefore,  and  sometimes  observations  on  the  heart  may 
well  be  made  the  same  day  as  experiments  on  the  sartorius  or  gastroc- 
nemius. 

VI.     THE  PHYSIOLOGY  OF  MUSCLE. 

Expt.  35. — The  nerve-muscle  'preparation  is  made  out  of  the  bipen- 
niform  gastrocnemius  muscle,  the  whole  sciatic  nerve,  and  the  femur  of  a 
large  frog.  Quick  and  painless  is  the  killing  of  the  animal  by  disorganiz- 
ing its  brain  and  cord  with  a  "seeker,"  which  is  thrust  into  the  skull- 
cavity  through  the  foramen  magnum  by  a  single  strong  quick  movement 
at  a  point  to  be  felt  with  the  thumb-nail  as  a  slight  transverse  depression 
in  the  spinal  column.  Now  with  small  scissors  cut  the  skin  circularly 
around  the  lower  part  of  the  trunk,  and  seizing  the  skin  on  the  back, 
draw  it  off  the  legs  with  one  pull.  Cut  the  frog  in  two  transversely  and 
then  separate  the  legs,  etc.,  by  an  incision  with  the  scissors  exactly  in  the 
median  line.  Now  dissect  out  the  conspicuous  sciatic  nerve  from  the 
knee  through  the  thigh  to  the  spinal  cord,  leaving  attached  to  it  a  small 
bit  of  the  latter  and  the  gastrocnemius  muscle.  Detach  the  tendo 
Achillis  from  the  bone  and  raise  the  gastrocnemius  muscle  with  the  for- 
ceps by  this  tendon.  Cut  through  the  middle  of  the  femur  (to  be  used 
as  a  handle),  leaving  it  attached  to  the  gastrocnemius.  This  is  the 
^'nerve-muscle  preparation"  so  much  used  in  physiology.  The  removal 
of  both  preparations  complete  from  the  frog  should  require  not  more 
than  five  minutes  after  it  has  been  done  two  or  three  times.  The 
preparation  that  is  not  to  be  used  at  once  should  be  placed  on  the  glass 
plate  and  covered  with  filter-paper  wet  in  modified  Ringer's  (Locke's)  solu- 
tion, the  closest  practicable  approach  to  blood-plasma.  The  nerve  should 
be  touched  only  by  the  glass  rod,  and  never  stretched  nor  allowed  to 
approach  dryness.  The  muscle,  too,  should  be  handled  as  little  as  pos- 
sible (especially  with  metallic  implements)  and  kept  wet.  Every  stimu- 
lation of  whatever  sort  of  these  now  dying  tissues  shortens  materially 
their  life  and  their  experimental  usefulness. 

The  gastrocnemius  muscles  and  the  sciatic  nerve  are  the  most  useful 
for  the  purposes  of  these  studie's  for  several  reasons.  They  are  easily 
and  quickly  dissected;  the  nerve  is  tlie  longest  and  largest  in  the  body; 
the  muscle  is  distinct;  it  is  of  tlie  bipenniform  type  and  thus  very  powerful; 


THE  PHYSIOLOGY  OF  MUSCLE 


481 


Fig.  268 


and  it  has  attached  to  it  a  long  bone  useful  as  a  means  of  hoUHng  it 
firmly  in  the  apparatus.  The  advantages  of  frogs  over  other  animals 
for  this  purpose  are  numerous,  but  the  selection  is  confined  to  poikilo- 
therms  ("cold-blooded"  animals),  because  in  them  the  muscles  when 
properly  cared  for  will  live  days  in 
comparison  with  the  hours  which  the 
muscles  of  homotherms  can  l)e  kept 
alive  with  only  much  greater  care. 

One  thing  it  is  pleasant  to  contin- 
ually remember:  that  any  consider- 
able injury  to  the  brain  or  even  to  the 
spinal  cord  produces  most  certainly, 
without  any  doubt  whatever,  com- 
plete abolition  of  consciousness  and 
the  pain-sense,  leaving  the  animal  a 
mechanism  only,  composed  of  slowly 
dying  tissues  of  great  scientific  use- 
fulness. 

Expt.  36. — Varieties  of  Energy  that 
will  Stimulate  Muscle. — (Apparatus : 
Gastrocnemius  muscle,  glass  plate, 
glass  rod,  key,  dry-cell,  wires,  satu- 
rated solution  sodium  chloride,  Bun- 
sen  burner,  seeker,  ice,  small  beaker.) 
Muscle  can  be  stimulated  by  four  of 
the  eight  known  aspects  of  energy  in 
addition  to  the  normal  nervous  force 
of  unknown  nature.  These  four  are: 
(.4)  kinetic,  (B)  electric,  (C)  chemic, 
and  (D)  thermic  energy. 

A.  Kinetic  Stimulation. —  As  the 
muscle  lies  on  the  glass  plate  prod  it 
with  the  small  sharp  end  of  the  glass 
rod,  or  pinch  it.     It  will  contract. 

B.  Electric. — Hold  the  wires  on  the 
muscle  and  close  the  key  (the  "make" 
of  the  current).  The  muscle  twitches. 
Open  the  key  ("break")  and  the 
muscle  contracts  again  (but  not  so 
strongly).  Static  electricity  will  stim- 
ulate as  well  as  galvanic. 

C.  Chemic. — Place  a  small  drop  of  the  saturated  sodium  chloride 
solution  on  the  muscle.  It  will  soon  contract.  Wash  the  muscle. 
Drying  (loss  of  water  from  the  protoplasm)  stimulates  the  muscle,  as 
may  be  seen  by  allowing  it  to  partially  dry,  Exosmosis  of  salines  is  a 
stimulation:  immerse  the  muscle  in  a  beaker  of  distilled  water.  Con- 
tractions soon  appear 

31 


The  frog's  nervous  system :  01,  olfactory 
nerves;  0,  eye;  Op,  optic  nerve;  Vg,  Gas- 
serian  ganglion  ;  Xg,  vagal  ganglion; 
Spn  1,  first  spinal  nerve;  Br,  brachial  nerve; 
Sg  1  to  Sg  10,  the  ten  ganglia  of  the 
sympathetic;   Js,  ischial  ners-e.      (Ecker.) 


482 


APPEXDIX 


D.  Thermic. — Apply  gently  very  close  to  the  muscle  a  large  very  hot 
wire.  It  will  contract.  Gently  apply  the  dried  wire  made  very  cold  by 
immersion  in  salted  ice.     It  will  perhaps  contract  again. 

E.  Normal  stimulation  of  muscle  is  a  universal  experience  in  our 
bodies. 

Exp.  37. — Analysis  of  the  Contraction  of  Cross-striated  Muscle. — 
(Apparatus:  Kymograph,  etc.,  for  graphic  record  of  gastrocnemius' 
contraction,  altogether  called  a  myograph,  electro-magnetic  signal, 
tuning-fork.)  Raise  the  drum  off  its  friction-bearing.  Place  the  signal 
in  the  primary  circuit  and  arrange  it  to  write  as  closely  as  possible  under 
the  muscle-lever.  Have  some  one  hold  tuning-fork  so  as  to  write  just 
below  or  above  the  signal.  Rotate  the  drum  and  so  draw  an  abscissa 
line.     Pass  maximal  make  induction-shocks  (cutting  out  breaks)  through 

Fig.  269 


Apparatus  as  set  up  by  students  to  make  a  simple  myogram.      The  drum,  however,  should 
have  been  at  the  top  of  its  spindle  when  the  first  curve  was  made. 

the  muscle  while  drum  is  spinning  at  a  rate  that  makes  the  contraction- 
curve  (myogram)  four  or  five  centimeters  long.  The  height  should  be 
about  three  centimeters.  The  signal  registers  the  moment  of  the  muscle's 
stimulation,  and  the  fork  measures  the  elapsed  time.  Drop  perpendic- 
ulars (or  arcs)  from  summit  of  contraction  curve,  and  mark  the  begin- 
ning and  the  end  of  the  curve.  Measure  in  hundredths  of  a  second  (A) 
the  combined  latent-period;  (B)  the  period  of  contraction;  and  (C)  the 
period  of  relaxation. 

In  analyzing  the  different  parts  of  the  myogram  from  a  cross-striated 
mu.scle  one  has  to  consider  (1)  the  electrical  latent  period,  (2)  the  mechani- 
cal latent  period,  (3)  the  period  of  contraction,  and  (4)  the  period  of  relax- 
ation. None  of  these  are  constant  in  muscles  generally,  even  in  the  cross- 
striated  muscles  of  the  same  iiiflividual  animal,  for  the  various  elements 
vary  according  to  many  contHtions  in  the  muscle  itself,  with  its  shape, 


THE  PHYSIOLOGY  OF  MUSCLE  483 

function,  nutrition,  irritability,  etc.  As  to  the  frog's  gastrocnemius, 
the  electrical  latent  'period  (the  interval  between  stimulation  and  the 
beginning  of  negative  variation  in  the  electrical  state  of  the  muscle)  is 
not  over  0.001  second.  The  mechanical  latent  period  is  the  interval 
between  stimulation  at  the  end  of  the  electrical  latent  period  and  the 
beginning  of  actual  movement  by  the  muscle.  This  period  is  about 
0.005  second  long.  Thus  the  "combined  latent  period"  in  the  frog's 
gastrocnemius  in  summer  is  not  over  0.006  second  normally.  In  addition 
to  this  about  0.004  second  is  taken  up  by  the  passage  of  the  nervous 
impulses,  making  altogether  0.010  second.  This  combined  quantity  is 
what  is  measured  in  the  laboratory  as  the  "latent  period."  In  winter 
it  may  be  somewhat  longer,  and  when  the  muscle  still  has  blood  circu- 
lating in  it,  shorter. 

Study  of  the  uprise  of  the  lever  (requiring  about  0.05  second  on  the 
average  in  the  gastrocnemius)  indicates  that  the  contraction  begins 
slowly  and  ends  slowly,  the  slow  beginning  occupying  about  0.005  second 
and  the  slow  ending  say  0.015  second.  The  shape  of  this  part  of  the 
myogram  depends  on  many  different  conditions.  The  downfall  of 
the  lever  {relaxation  of  the  muscle)  occupies  about  0.075  second;  it 
begins  slowly  (0.015  second)  and  ends  slowly  (0.01  second). 

Expt.  38. — Galvanic  Electricity  as  a  Stimidus. — (Apparatus:  Muscle, 
myograph  or  graphic-record  apparatus,  rheocord,  tuning-fork.)  Set  up 
the  mechanism  for  making  graphic  records  of  the  frog's  gastrocnemius, 
connecting  the  muscle  through  a  key  and  rheocord  with  one  dry  cell. 
Raise  the  drum  from  the  friction-bearing  and  spin  it  slowly.  Apply  the 
tuning-fork  and  close  the  key,  holding  the  lever  down  and  using  a  current 
only  just  strong  enough  to  produce  contraction.  Now  open  the  key  and 
observe  that  no  contraction  then  occurs :  the  galvanic  make  is  a  stronger 
stimulus  than  is  the  break.  Again,  with  full  strength  of  current,  make 
records  of  make  and  of  break  (here,  as  always,  separated  by  holding  the 
key  closed  while  mnscle  contracts  and  relaxes  from  the  make),  and  observe 
that  the  make-contraction  is  the  more  vigorous,  the  lever  rising  higher 
than  from  the  break-shock. 

Observe  also  that  in  case  of  skeletal  muscle  no  general  contraction 
occurs  during  the  passage  of  the  constant  current,  but  only  at  its  make 
and  break.  The  muscle,  however,  is  meanwhile  in  the  interesting  electro- 
tonic  condition. 

That  the  make  or  application  of  the  constant  galvanic  current  is  a 
stronger  and  more  effective  stimulus  than  is  the  break  or  withdrawal  of 
the  current  needs  no  special  explanation.  The  addition  of  energy  would 
naturally  result  in  more  activity  than  the  withdrawal  of  energy  already 
present.  It  is  owing  in  part  to  the  sudden  change  in  the  strength  of 
the  stimulus  (Du  Bois  Reymond)  that  any  contraction  takes  place  at  the 
break  of  the  galvanism.  (See  the  next  experiment.)  There  has  arisen, 
however,  an  elaborate  system  of  explanation  based  on  phenomena  whose 
meaning  is  obscure:  In  the  case  of  galvanic  stimulation,  the  excitation 
on  making  or  closing  the  constant  current  begins  at  the  cathode  (C.C.),  and 


484  APPEXDIX 

on  breaking  or  opening  the  current  at  the  anode  (A.O.).  Von  Bezokl 
first  demonstrated  this  after  experiments  by  Schiff  more  than  fifty  years 
ago.  Still  no  explanation  worthy  of  the  name  is  forthcoming,  and  the 
best  that  can  be  said,  apparently,  is  that  when  the  current  is  applied 
("make"),  the  muscles'  irritability  is  increased  at  the  cathode  more  than 
at  the  anode,  and  so  the  contraction  starts  powerfully  at  the  former  pole; 
while  when  the  current  is  removed  ("break"),  the  irritability  is  greater 
at  the  anode  than  at  the  cathode  (but  less  than  at  the  cathode  on  making). 
^Mien  we  have  learned  the  facts  about  the  nervous  impulse  and  muscular 
contraction  these  "explanations"  may  seem  less  pedantic  and  more  use- 
ful than  at  present. 

See  also  Expts.  59,  60,  and  80,  the  phenomena  being  essentially  the 
same  in  nerve  as  in  muscle. 

Expt.  39. — Induced  Electricity  as  a  Stimulus. — Insert  the  inductorium 
arranged  for  single  shocks  in  place  of  the  rheocord  of  the  last  experiment. 
Draw  or  turn  the  secondary  coil  far  enough  away  from  the  primary  so 
that  a  make-shock  on  closing  the  simple  key  will  just  not  cause  a  contrac- 
tion. Hold  the  key  closed  and  meanwhile  observe  that  no  contraction 
occurs  during  the  passage  of  the  galvanic  current  through  the  primary 
coil,  for  induced  electric  currents  are  always  of  only  momentary  duration. 

Open  the  simple  key.  Contraction  then  occurs,  demonstrating  that 
the  induced  break-shock  is  a  stronger  stimulus  than  the  induced  make- 
shock.  This  excess  is  due  to  the  absence  from  the  break  of  the  "extra- 
currents"  which  make  less  sudden  the  make-shock  (as  demonstrated 
previously).  Repeat  with  various  strengths  of  induced  electricity,  and 
see,  and  feel  on  the  tongue,  that  the  break  is  a  much  stronger  stimulus 
than  is  the  make;  the  opposite  is  true  with  the  simple  galvanic  current. 

The  extra-currents  referred  to  as  the  cause  of  the  lessened  stimulating 
effect  of  the  make-shock  are  inductively  generated  in  contiguous  rounds 
of  the  wire  of  the  primary  coil  of  the  inductorium,  just  as  induced  cur- 
rents are  generated  between  the  rounds  of  the  primary  and  the  secondary 
coils.  These  currents  are  in  direction  opposite  to  the  regular  currents, 
and  it  is  tlieir  opposition  that  makes  the  rise  to  full  strength  of  the  regular 
current  gradual  instead  of  sudden.  (See  Expt.  44.)  As  regards  the  break 
of  the  regular  induced  current  (a  stronger  stimulus  than  the  make): 
when  the  primary  current  is  shut  off  both  the  regular  current  and  the 
extra  current  cease  at  once,  and  the  suddenness  of  the  change  of  strength 
of  stimulus  is  maximal,  greater  than  in  case  of  the  make,  and  so  stimulates 
more  strongly. 

Expt.  40. — Duration  of  Stimulus  Affects  Contraction. — (Apparatus: 
Mvogra])!!,  induftorium,  commutator  without  cross-wires,  two  cells, 
sartorius.J  Attacli  one  cell  to  the  iiuhictorium  for  single  break-shocks 
and  connect  the  secondary  coil  with  the  two  posts  of  one  side  of  the 
commutator.  Connect  the  other  cell  directly  with  the  posts  of  the 
opposite  side  of  commutator.  Connect  the  rocker  of  the  commutator 
with  the  sartorius  myograph  in  the  usual  way.  Have  the  drum  rotate 
at  its  maximum  gear-speed.  Write  an  abscissa  line.  Send  a  maximal 
break  induction-shock  through  the  muscle.     Lower  the  drum  and  write 


THE  PHYSIOLOGY  OF  MUSCLE 


485 


another  abscissa  line  5  cm.  below  the  other.  When  the  drum  has  rotated 
at  same  speetl  as  before  to  the  place  of  the  first  curve  shift  the  rocker, 
thus  sending  a  galvanic  make-shock  through  the  muscle.  Compare  the 
two  curves.  The  former  curve,  made  with  the  exceedingly  sudden  induc- 
tion break  shock  will  be  found  to  be  more  acute  than  that  made  by  the 
continuous  galvanic  current. 

This  briefly  sustained  contraction  of  the  cross-striated  muscle  (it  is 
longer  in  smooth  muscle)  when  stimulated  with  the  galvanic  shock  is 
doubtless  due  to  a  condition  of  brief  electrotonus,  which  has  no  existence 
when  the  muscle  is  stimulated  with  the  almost  instantaneous  induced 
shock.  The  reason  that  the  myogram  is  broader  on  top  (indicating  a 
sustained  contraction)  is  that  the  stimulus  in  case  of  galvanism  lasts 
longer  than  it  does  in  case  of  electricity  produced  by  induction.  To 
stimulate  a  cross-striated  muscle  requires  a  duration  of  a  galvanic  current 
of  at  least  0.001  second,  while  to  have  maximal  contraction  of  a  smooth 
muscle  the  electricity  must  be  applied  from  0.25  to  5  seconds. 


Fig.  270 


Threshold    Stimulus,     Galvanic 


Threshold   Stimulus,     Induced 


These  curves  show  in  general  the  relations  of  the  degree  of  contraction  of  cross-striated 
(frog's  gastrocnemius)  muscle  to  various  intensities  of  stimulus,  beginning  at  the  threshold  and 
ending  at  the  maximum.  The  left-hand  set  of  curves  was  made  with  galvanic,  the  right-hand 
set  with  induced,  electricity.  To  be  read  from  left  to  right.  Constant  load  of  10  gms. 
Jntervals  between  contractions  about  thirty  seconds.      Reduced. 

Expt.  41. — The  Threshold  and  the  Maximum  Stimidation. —  (Apparatus : 
Myograph,  rheocord,  inductorium.) — (.4)  Galvanism.  Place  the  block  of 
the  rheocord  so  that  the  make  of  the  current  just  does  not  produce  con- 
traction. By  gradually  moving  the  slider,  increase  the  current  with  the 
key  closed  until  the  make  of  the  current  just  barely  causes  contraction. 
IMake  a  record  (straight  vertical  line)  of  the  contraction  on  the  drum 
while  stationary;  move  the  block  a  few  centimeters  so  as  to  increase  the 
stimulus,  turn  drum  0.5  centimeter  by  hand  and  make  another  record — 
and  so  on.  A  series  of  contractions  up  to  the  maximum  of  the  cell  is 
thus  produced. 

(5)  Induction. — Repeat  the  experiment,  using  the  induction-coil 
instead  of  the  rheocord,  cutting  out  (with  short-circuiting  key  on  the 
secondary  coil)  all  the  make:shocks.  Compare  this  series  with  that 
made  with  make  galvanic  shocks.  Observe  the  threshold;  the  increase 
in  contraction;  and  that  a  place  is  soon  reached  above  which  no  strength 
of  current  would  increase  the  contraction,  but  rather  injure  the  muscle. 


486 


APPEXDIX 


The  existence  of  the  threshold  is  universal  wherever  protoplasm  is 
cwicemed.  If  a  sound-stimulus  be  too  faint  our  ears,  as  mechanisms, 
are  not  set  in  action  owing  to  their  inevitable  inertia,  and  we  hear  no 
somid;  if  a  light  be  too  faint,  our  eyes  fail  to  see  it.  The  threshold  is  a 
necessary  accompaniment  of  the  inertia  of  matter,  organic  and  inorganic. 

The  maximum  stimulation  of  a  tissue  is  of  a  similar  nature  logically. 
A  mechanism  can  work  only  so  hard,  a  string  can  vibrate  only  so  far. 
When  a  muscle  has  received  a  stimulation  which  corresponds  with  the 
maximum  of  its  action,  any  increase  in  strength  of  the  stimulus  up  to  a 
certain  degree  wdll  produce  only  the  same  maximal  effect.  Beyond  that 
certain  degree  of  strength  of  stimulus  the  organism  will  be  injured  and 
its  activity  impaired  in  all  directions. 

Expt.  42. — Threshold  Independent  of  Load. — Repeat  the  latter  half 
of  Experiment  41,  using  no  load  instead  of  10  gm.,  which  is  a  fair  load. 
Repeat  again,  using  50  gm. 

Fig.  271 


The  relation  of  cross-striated  muscle's  contraction  to  the  increasing  strength  of  its  stimulation 
by  induced  electricity.  The  strength  of  the  induced  break-shocks  increased  by  degrees,  each 
represented  on  the  inductorium  by  one  notch  of  the  vertical  arc-index,  then  by  3  mm.  on  the 
horizontal  scale.  To  be  read  from  left  to  right.  Intervals,  ten  seconds.  ^  (The  greater  contraction 
seen  near  the  end  is  unexplained.)  Observe  that  even  ten  seconds  apart,  the  electric  shocks 
fatigue  the  muscle,  le.ssening  both  its  contraction  and  its  relaxation. 


It  is  not  obvious  why  the  threshold  should  be  in  any  way  dependent 
on  the  muscle's  load,  for,  unless  the  load  be  so  excessive  as  to  tear  apart 
the  muscular  fibers,  it  does  not  affect  in  any  way  the  action-conditions 
of  the  mu-scle,  either  in  pulling  apart  the  sarcomeres,  or  in  disturbing 
the  relations  of  the  nerves  to  the  muscle.  As  a  matter,  however,  of 
precise  fact,  load  does  influence  in  one  respect  the  threshold,  for  a  muscle 
works  more  normally  in  all  respects  when  it  has  a  moderate  load 
than  when  it  has  too  little  or  too  much.  This  normal  load  apparently 
keeps  up  the  normal  tonus  of  the  organ  (mu.scle)  and  this  in  all  sorts 
of  ti.ssues  is  a  pre-requisite  of  optimum  action.  It  cannot  be  doubted, 
then,  that  the  threshold  would  be  found  slightly  lower  in  a  muscle  with 
a  normal  load  than  in  one  quite  unloaded. 

Expt.  43. — Contraction  of  Smooth  Muscle. — (Apparatus:  Myograph, 
signal.)  Cut  four  or  more  rings  out  of  the  frog's  stomach,  tie  them 
together  in  a  line  with  hue  copper  wire,  and  place  this  long  line  of  rings 
as  the  gastrocnemius  is  usually  placed.  Use  two  cells,  and  put  the  signal 
in  the  circuit.  Let  the  lever  write  carefully  a  fine  abscissa  line.  Stimu- 
late this   stomach-muscle  with   one  pair  of  maximal  make-and-break 


THE  PHYSIOLOGY  OF  MUSCLE  487 

galvanic  shocks  and  record  on  the  drum  going  at  the  minimal  speed  of 
its  mechanism.  Compare  (1)  its  latent  period  (several  seconds)  with 
that  of  striated  muscle;  (2)  its  period  of  contraction  (thirty  seconds  or  so) ; 
(3)  its  period  of  relaxation  (one  minute  or  so);  (4)  the  general  shape  of 
the  curve.  (All  these  quantities  are  very  variable  with  many  varying 
conditions.)  These  two  sorts  of  muscle  are  obviously  very  different  in 
their  functional  habits,  yet  they  are  less  different  than  is  sometimes  sup- 
posed. (The  "intermediate"  variety,  that  of  the  heart,  will  be  studied 
later  on.) 

To  understand  the  great  differences  between  the  modes  of  contraction 
of  cross-striated  and  of  smooth  muscle,  it  is  necessary  to  recollect  their 
respective  structures.  A  smooth  muscle-fiber  is  functionally  all  one 
piece  of  protoplasm,  massive,  and  with  relatively  much  inertia.  A 
cross-striated  muscular  fiber,  on  the  other  hand,  is  made  up  of  very 
numerous  minute  portions,  each  of  which,  so  far  as  function  (contraction), 
is  concerned,  is  practically  a  separate  muscle-fiber,  and  one  constructed 
with  the  greatest  readiness  for  action.  Thus,  in  cross-striated  muscle 
the  inertia  is  divided  into  many  parts,  and  the  muscle  therefore  contracts 
very  rapidly  and  very  vigorously.  The  difference  between '  them  is 
not  unlike  that  between  a  galvanic  battery  made  up  of  numerous  small 
cells  and  one  composed  of  only  one  cell  with  large  elements.  The  elec- 
trical organ  of  electrical  fishes  makes  this  comparison  apt,  for  it  is  cross- 
striated  muscle  modified  to  produce  an  electric  shock  of  high  intensity, 
and  composed  of  hundreds  of  cells  like  the  former  of  the  two  batteries 
above  suggested.  In  a  striated  muscle  the  effect  is  usually  sudden  and 
powerful  and  of  relatively  short  duration,  as  its  structure  implies,  while 
in  smooth  muscle,  acting  with  large  and  relatively  few  elements  (cells) 
the  contraction  is  generally  the  relatively  slow,  steady,  contraction  and 
relaxation  we  should  expect  to  find  in  the  vegetative,  as  distinguished 
from  the  voluntary  organs.  In  this  particular  experiment  with  the 
frog's  stomach  the  difference  between  the  two  sorts  of  muscle  is  perhaps 
unfairly  exaggerated  because  these  smooth  fibers  are  circular  fibers,  and 
thus  give  only  half  as  much  linear  shortening  when  the  rings  are  thus 
connected  as  they  would  if  spread  out  their  full  length  as  are  the  fibers 
in  the  cross-striated  muscle  compared  with  them. 

The  danger  in  this  experiment  is  that  the  contraction  will  not  be 
appreciated  because  of  its  small  degree  and  its  very  long  periods. 
Sometimes  an  active  relaxation  apparently  complicates  matters.  ^Nlore- 
over,  the  stomachs  of  winter  frogs  may  be  very  loth  to  react,  either  wav. 

Expt.  44. — Stulden  Change  and  Gradual  Change  of  the  Strength  of 
Stimidus. — (Apparatus:  Myograph,  rheocord,  two  simple  keys.)  (.4) 
Sudden  Change. — Set  up  the  apparatus  carefully  as  follows:  Put  two 
wires  into  each  of  the  two  binding-posts  of  simple  key  Xo.  1,  and  connect 
one  wire  from  each  post  with  one  dry  cell.  Of  the  other  two  wires,  run 
one  to  the  anode  of  the  other  dry-cell  and  the  other  to  the  femur-clamp. 
From  the  remaining  plate,  the  cathode  of  cell  No.  2,  run  a  wire  to  simple 
key  Xo.  2,  and  connect  the  other  post  of  this  key  with  the  muscle-lever. 


488  ""  APPENDIX 

Hold  key  Xo.  1  closed.  Without  making  a  curve  (using  the  myograph 
merely  to  see  better  the  contraction),  close  key  No.  2  and  hold  it  closed, 
whereupon  the  make-current  from  the  second  cell  will  stimulate  the 
muscle.  Now,  with  this  current  still  passing  through  the  muscle,  open 
key  No.  1,  which  lets  the  current  from  cell  No.  1  into  the  circuit  and 
doubles  the  intensity  of  the  stimulus.     The  muscle  then  contracts  again. 

(B)  Gradual  Change. — Hitch  the  two  dry-cells  in  series,  and  interpose 
between  them  and  the  myograph  a  simple  key  and  the  rheocord.  Place 
the  block  of  the  rheocord  against  the  anodal  binding-post  and  close  the 
key.  Now  slide  the  block  along  the  meter  of  wire  visible  on  the  rheocord 
to  its  end  and  observe  that  no  contraction  occurs  although  the  stimulus 
has  risen  from  below  the  threshold  to  far  above  it.  Raise  the  block  off 
the  wire  and  replace:  there  is  active  contraction  from  this  sudden  stimu- 
lation although  no  stronger  than  before. 

Expt.  45. — Summation  of  Singly  Inadequate  Stimidi. — (Apparatus: 
Inductorium,  frog).  (A)  In  Reflexions. — Tie  the  wires  from  the  secondary 
coil  about  a  frog's  foot  not  too  close  together.  Stimulate  with  make- 
shocks  below  the  threshold  for  reflex  contraction  of  the  leg.     Soon  the 

Fig.  272 


' 1 1 ri  I  I  I  I  i  I  I  I  I  I  I  I  1 1  I  I  I  I  1  1 1  I  I  I  I  I  I  I  I  I  i 


Summation  of  singly  inadequate  stimuli,  to  show  a  probable  katabolie  influence  on  protoplasm. 
At  intervals  of  three  seconds  a  frog's  gastrocnemius  was  stimulated  with  break-shocks,  each  too 
weak  to  produce  a  contraction.  After  about  sixty  such  stimulations  contraction  occurred.  (To 
be  read  from  left  to  right.)  The  time-line  is  in  three-second  intervals.  This  result,  made  on 
a  "winter-frog,"  is  not  like  that  seen  in  the  "summer-frog." 

influences  summate  and  the  leg  is  flexed.  (B)  In  a  Single  Muscle. — Place 
the  secondary  coil  so  that  the  single  break-shock  is  just  below  the  thres- 
hold-intensity. After  the  muscle  has  fully  recovered  from  the  stimulation 
of  this  threshold-finding,  let  a  break-shock  pass  through  the  muscle 
(always  excluding  makes)  and  repeat  at  intervals  of  four  or  five  seconds 
by  the  watch.  These  stimuli  after  a  time  will  summate  to  an  effective 
stimulus,  and  the  muscle  will  contract. 

This  experiment  studies  the  summation  of  the  occasion  of  contraction 
just  as  the  next  experiment  deals  with  the  effect.  It  demonstrates  that 
even  a  subliminal  stimulus  (one  below  the  threshold-strength)  has  an 
effect  on  protoplasm  which  persists  in  some  form  at  least  five  seconds 
(in  fact,  twice  that  time  at  least).  We  see  this  frequently  in  the  sensory 
realm  also.  (See  Chapter  XH.)  The  precise  nature  of  the  impression 
made  on  protoplasm  by  subliminal  stinnili  cannot  be  stated,  but  it  lies 
probably  in  the  direction  of  increasing  slightly  each  time  the  tonus  or 
irritability  of  the  tissue. 

Exjyt.  46. — Superposition  of  Contractions. — (Apparatus :  Myograph  and 
inductorium.)  Arrange  apparatus  for  writing  myograms  through 
single  maximal  shocks,  the  drum  rotating  at  its  maximum  gear-speed. 


THE  PHYSIOLOGY  OF  MUSCLE  4S9 

Stimulate  by  make-and-break  shocks  separated,  as  usual,  so  that  the 
curve  from  each  is  complete.  Now  reduce  the  interval  between  the 
break  and  the  make  until  relaxation  is  prevented  by  a  second  contrac- 
tion arising  from  the  break-shock.  A  compound  curve  is  thus  formed, 
the  second  part  mucji  higher  than  the  first.  Compare  this  height  with 
that  from  a  single  break  shock. 

Fig.  273 


A S- 


The  mechanical  nature  of  muscular  tetanus.  If  electrical  stimuli  be  applied  to  a  frog's  gas- 
trocnemius often  enough,  the  muscle  does  not  have  time  to  relax  before  it  is  made  to  contract 
again.  Observe  that  the  more  frequent  the  stimulation  the  more  slowly  the  muscle  relaxes  when 
the  stimulation  stops.      To  be  read  from  left  to  right.      The  time-line  is  in  seconds. 

This  superposition  of  contractions  suggests  the  nature  of  the  contracted 
condition  known  as  muscular  tetanus  (not  to  be  confused  with  the  disease 
tetanus  or  lockjaw).  As  has  been  seen  already,  relaxation  of  even  a 
cross-striated  muscle  requires  time  (0.075  second),  and  if  another  stimu- 
lus is  imposed  upon  the  muscle  before  it  has  fully  relaxed,  another  con- 
traction will  at  once  occur.  Because  the  latent  period  of  contraction  is 
much  shorter  than  the  relaxation -period,  the  two  myograms  or  curves 


490 


APPEXDIX 


will  fuse.  This  is  the  mechanical  condition  of  things  in  this  experiment. 
The  shape  of  the  curve,  of  course,  depends  chiefly  on  the  time-relations 
of  the  two  stimulations.     (See  Expts.  05  and  OS.) 

Expt.  47. — Tetanus. — (Apparatus:  Same  as  in  last  experiment.) 
Using  the  key,  stimulate  the  muscle  at  first  slowly  and  then  more|fre- 
quently,  making  a  curve  for  each  speed.  Determine  how  many  stimula- 
tions per  second  are  necessary  in  order  that  the  muscle  may  not  have 
time  to  relax  at  all,  thus  writing  a  curve  smooth  on  top,  but  up-hill 
somewhat. 

This  condition  is  practically  a  continuation  of  the  last  experiment. 
Here  the  stimuli  are  so  frequent  that  the  muscle  has  no  chance  to  me- 
chanically relax  to  any  degree,  and  the  resulting  myogram  becomes 
essentially  a  smooth  line.     The  number  of  stimulations  per  second 

Fig.  274 


Apparatii",  as  set  ui)  by  students  to  study  the  sui)erimposed  fatigue-curve  of  muscle. 

required  to  occasion  complete  tetanus  depends  largely  on  tlie  condition 
of  the  muscle;  fatigue,  for  example,  renders  slower  the  relaxation  (as 
well  as  the  contraction),  reducing  the  number  of  stimuli  per  second 
required  to  produce  this  condition.  Typical  tetanus  may  be  made 
with  in(hicti(^M-sh()cks  coming  at  the  rate  of  from  30  to  100  per  second. 
]\Iuscular  tetanus  is  of  relatively  small  theoretical  importance. 

Expt.  48. — Eatigue. — (Apparatus:  IMvograph  with  attachment  for 
breaking  circuit  at  each  rotation  of  the  drum,  signal,  inductorium,  two 
stand-rods,  two  feinur-claiups,  and  strip  of  spriiig-l)rass.)  Put  signal 
and  femur-clamp  hohHiig  the  brass  strip  and  signal  on  one  stand-rod, 
and  the  myograph  on  the  other.  Arrange  the  inductorium  for  making 
maximal  signal-shocks,  placing  signals,  key  and  automatic  circuit- 
maker  in  the  primary  circuit;  the  myograph  is  in  the  secondary  circuit. 
Keep  the  kymograph  fully  wound,  or,  better,  turn  llic  drum  with  an  elec- 


THE  PHYSIOLOGY  OF  MUSCLE  491 

trical  motor.  Load  gastrocnemius  with  50  gm.  Use  the  maximum  speed 
of  the  drum.  As  thus  arranged,  when  the  key  is  closed  each  rotation  of 
the  drum  will  stimulate  the  muscle  and  the  myograms  will  be  super- 
imposed, thus  allowing  of  direct  comparison  of  the  succeeding  curves 
as  the  muscle  becomes  gradually  fatigued.  Keep  up  the  experiment 
(with  the  kymograph  always  well  wound)  until  the  curves  are  nearly 
flat.  Note  in  your  books  the  characteristic  shape  of  the  myograph  at 
first,  midway,  and  at  the  last,  and  also  the  changes  in  the  different  parts 
of  the  myogram.  If  only  every  tenth  contraction  is  recorded  the  curves 
will  be  more  easily  discriminated. 

The  phenomena  of  fatigue  in  muscle  are  of  great  importance,  for  it  is 
by  muscular  contraction  that  events  are  accomplished  in  animal  life, 
whether  it  be  the  signing  of  a  name,  the  starting  of  a  machine,  or  the 
composition  of  a  symphony.  By  thus  superimposing  the  curves  fatigue- 
differences  are  strongly  brought  out  as  follows : 

At  first  the  curves  (the  degree  of  contraction)  increase  slightly  in  height 
as  the  muscle  gets  into  its  best  working  order.  Then  they  get  gradually 
flatter,  and  at  length  are  little  more  than  straight  lines.  The  chief 
characteristic  of  the  fatigued  condition  of  muscle  is  a  slowing  in  the 
processes  making  up  the  total  complex  curve.  The  latent  period 
increases  much,  from  0.006  second  to  0.3  second  or  so.  The  contraction- 
time  increases  somewhat,  but  the  most  marked  change  is  in  the  length- 
ening of  the  relaxation-time.  This  is  increased  many  times,  and  when 
so  increased  the  condition  is  sometimes  called  "contractur."  After  four 
or  five  thousand  contractions  this  slowness  of  relaxation  gradually 
decreases,  but  never  disappears  so  that  the  muscle  relaxes  as  quickly 
as  when  unfatigued. 

Heat  markedly  hastens  the  onset  of  fatigue,  as  also  does  an  abnormally 
large  load,  ^^^lite  muscle  (in  the  rabbit,  etc.)  is  more  easily  fatigued 
than  red  muscle,  and  similarly,  a  supply  of  blood  through  the  muscle 
retards  fatigue.     Recovery  takes  place  rapidly  during  rest. 

Expt.  49. — Muscular  Tone. — (Apparatus:  Stand-rod,  femur-clamp, 
ether,  frog.)  Lightly  etherize  the  frog  and  fasten  him  belly  down  on 
the  frog-board.  Gently  open  the  lower  part  of  the  back  and  divide  the 
roots  of  the  exposed  sciatic  on  one  side.  Hang  up  the  frog  evenly  by 
the  lower  jaw  in  the  femur-clamp. 

On  careful  observation  from  directly  in  front  of  the  frog,  the  leg  whose 
motor,  sensory,  and  trophic  nerve  has  been  cut  will  be  seen  to  hang 
lower  and  to  be  more  limp  than  the  normal  leg.  The  tone  of  the  muscles 
being  lost,  gravity  draws  down  the  foot  farther  than  the  other. 

Expt.  50. — Action-current. — (Apparatus:  Two  nerve-muscle  prepara- 
tions with  long  nerves,  frog's  heart.)  This  experiment  has  long  been 
known  as  the  "rheoscopic  (current-showing)  frog."  (A)  On  the  gastroc- 
nemius. With  the  two  muscles  on  the  glass  plate,  lay  the  nerve  of 
muscle  No.  1  longitudinally  over  muscle  No.  2.  Stimulate  the  central 
end  of  the  nerve  of  muscle  No.  2  with  make  shocks  from  one  cell,  using 
the  platinum  electrode  for  the  purpose.     If  the  nerve  be  properly  arranged 


492  APPENDIX 

(use  the  glass  rod),  muscle  No.  1  will  be  stimulated  to  contraction  by 
the  action-current  passing  over  muscle  No.  2. 

B.  In  the  Heart. — Open  the  thorax  of  the  frog  from  which  the  two- 
nerve-muscle  preparations  were  taken  sufficiently  to  expose  the  still 
beating  heart.  AVith  the  glass  rod  arrange  the  nerve  of  a  gastrocnemius 
longitudinally  over  the  heart.  The  former  muscle  should  contract  at 
each  heart-beat.  If  it  does  not,  snip  off  the  central  end  of  the  nerve, 
place  it  on  the  heart's  apex  and  loop  the  nerve  over  so  that  it  touches  the 
base  of  the  heart;  or  even  slightly  injure  the  heart-apex  mechanically. 

It  is  demonstrated  by  these  experiments  merely  that  when  a  muscle 
contracts  under  experimental  conditions  an  appreciable  current  passes 
over  it,  or  at  least  that  a  difference  of  potential  is  developed  in  different 
parts  of  the  muscle.  Application  of  a  delicate  galvanometer  proves 
this  current  to  be  electrical.  It  may  be  easily  shown  that  it  precedes  the 
contraction  of  the  muscle  (see  Expt.  69),  and  that  in  case  of  stimulation 
through  a  nerve  the  current  starts  at  its  entrance-place  and  passes  over 
the  muscle.  (In  these  respects  the  contraction-wave  is  similar.)  When 
one  end  of  a  muscle  is  injured  so  as  to  contract  less  normally,  the  con- 
tracting end  is  electronegative  to  the  part  less  active.  In  an  active 
whole  muscle  points  near  its  equator  are  electro-negative  to  points 
farther  away.  The  rate  of  the  action-current  in  frog's  muscle  (and  nerve) 
is  about  3  meters  per  second,  its  average  duration  being  about  0.004 
second,  while  its  strength  in  a  frog's  gastrocnemius  is  about  0.08  volt. 
AMiether  an  electrical  current  accompanies  the  contraction-wave  just  as 
this  action-current  precedes  it  is  still  in  dispute.  Some  find  evidence 
that  this  electrical  condition  lasts  as  long  as  does  the  shortening  of  the 
muscle. 

Expt.  51. — Electricity  Developed  in  Necrobiosis.- — (Current  of  injury, 
demarcation-current.)  (Apparatus:  Capillary  electrometer,  normal 
saline  clay,  glass  rod,  nerve-muscle  preparations,  skin,  stomach.) 

(A)  Prepare  the  gastrocnemius  muscle  and  its  nerve  with  great  care, 
gentleness,  and  speed.  Even  with  a  capillary  electrometer  no  elec- 
tricity can  be  found  in  the  muscle  when  its  ends  are  connected  by  a  con- 
ductor (except  when  the  muscle  contracts,  and  that  is  its  action-current). 
Cut  oft"  the  lower  third  of  the  muscle  and  bring  the  end  of  the  sciatic 
against  the  cut  end.  The  remainder  of  the  muscle  contracts.  Apply 
the  electrometer  and  a  vigorous  current  will  be  found  in  the  muscle 
passing  from  the  injured  end  upward;  the  injured  surface  is  electro- 
negative to  the  uninjured  lateral  surface.  (B)  Try  the  inside  and  out- 
side of  the  frog's  skin  and  the  inside  and  outside  of  its  stomach.  The 
outside  is  electro-positive  to  the  inside  in  both  cases.  (0)  Roll  a  small 
Ijit  of  the  saline  clay  into  a  pencil  3  cm.  long  and  \  cm.  in  diameter  and 
bend  it  in  the  shape  of  U  on  the  dried  dissecting-plate.  Make  a  gastroc- 
nemius nerve-muscle  preparation.  Place  the  nerve  near  its  muscle  on 
one  arm  of  the  clay;  lift  the  other  part  of  the  nerve  with  the  glass  rod  and 
firop  the  freshly  cut  end  on  the  other  arm  of  the  clay.  The  muscle  will 
twitch,  stimulated  by  the  demarcation -current  from  the  nerve. 


THE  PHYSIOLOGY  OF  MUSCLE  493 

These  experiments  demonstrate  the  injury-current  of  the  tissues  and 
the  great  irritahiUty  of  nerve  as  well.  The  term  demarcation-current 
signifies  that  the  injury-current  originates  at  the  dividing-line  between 
the  normal  and  the  injured  tissue.  It  is  also  sometimes  ill-called  the 
current  of  rest.  The  direction  of  the  demarcation-current  is  always  from 
a  normal  point  round  through  a  connecting  conductor  to  an  injured 
point:  the  latter  is  "negative"  to  the  former.  Theories  as  to  the  cause 
of  the  demarcation-,  rest-,  or  injury-current  have  been  various,  one 
sort  "molecular"  and  the  other  chemical.  Du  Bois  Reymond  originated 
the  former,  and  especially  Hermann  and  Hering  have  elaborated  the 
latter  hypothesis.  This  chemical  theory  supposes  that  the  katabolic 
changes  consequent  on  injury  reduce  the  electromotive  force  of  the  part 
making  it  less  than  (negative  to)  that  of  the  normal  region.  These 
theories  apply  to  nerve  as  well  as  to  muscle. 

The  strength  of  this  current  is  much  smaller  in  nerve  than  in  muscle; 
in  the  former  its  strength  is  from  0.005  to  0.030  volt.  In  muscle  it  may 
reach  0.1  volt.  In  nerve,  owing  to  the  relatively  quick  death  of  the 
tissues,  it  rapidly  disappears.  Dead  protoplasm  gives  no  current  of  any 
sort,  nor  do  normal  tissues  so  far  as  we  know  except  when  functioning. 
It  is  then  only  in  necrobiotic  protoplasm  that  this  sort  of  electricity  is 
set  free.  Its  significance  is  not  as  yet  clear,  but  its  theoretical  importance 
is  obvious. 

Expt.  52. — Direction  of  Current  Affects  Contraction. — (Apparatus: 
AVax,  sartorius  muscle,  rheocord.)  Aiake  a  wax  trough  just  large 
enough  to  contain  the  sartorious  muscle,  and  place  the  moistened  muscle 
within  it.  Place  wires  from  the  rheocord  (block  and  anode)  on  either 
end  of  the  trough  and  close  the  key.  The  muscle  contracts.  Place  the 
wires  on  opposite  sides  of  trough  so  that  current  goes  exactly  across  the 
muscle  at  right  angles.  The  muscle  does  not  contract.  At  any  other 
angle  than  this  the  current  is  an  effective  stimulus.  Use  various  strengths 
of  the  electricity. 

It  is  not  easy  to  account  for  this  phenomenon  definitely,  but  there  are 
two  hypotheses.  One  is  that  the  lack  of  response  is  due  to  the  balancing 
of  the  two  opposed  influences  at  the  cathode  and  anode,  leaving  the 
resultant  zero.  This  could  occur  only  when  the  current  was  exactly 
transverse,  hence  the  difficulty  of  a  good  result.  At  45°  angle  the  result 
is  less  than  when  the  direction  of  the  current  is  along  the  fibers.  The 
second  "explanation"  lies  in  the  much  greater  resistance  shoAvn  to 
electricity's  passage  across  fibers  than  with  them.  In  nerve,  for  example, 
where  the  same  phenomena  obtain,  the  longitudinal  resistance  is  said  to 
be  2,500,000  times  the  resistance  of  a  like  length  of  mercury,  while  the 
transverse  resistance  of  nerve  is  12,500,000  times  greater.  In  these  cases 
the  electricity  might  not  pass  through  the  excitable  tissues  at  all. 

Expt.  53. — Unipolar  Induction. — (xVpparatus:  Inductorium,  four 
nerve-muscle  preparations.)  {A)  Make  four  nerve-muscle  preparations 
and  place  them  on  a  perfectly  dry  glass  plate  so  that  the  nerve  of  each 
shall  be  over  the  muscle  of  the  next  except  the  last.     Push  the  secondary 


494 


APPENDIX 


coil  completely  over  the  primary,  open  the  short-circuiting  key,  and  set 
the  vibrating  armature  in  motion  if  not  already  vibrating. 

Connect  one  binding-post  only  of  the  secondary  coil  with  the  first  of 
the  series  of  muscles.  One  after  the  others  will  contract  stimulated  by 
the  induced  electricity  "piled  up"  on  the  pole,  for  this  electricity  has 
many  of  tlie  characteristics  of  static  electricity. 

(B)  Remove  three  of  the  four  muscles,  and  while  the  remaining  one  is 
bemg  stimulated  as  before,  hold  a  moistened  finger  near  the  muscle. 
The  latter  will  contract,  the  stimulating  tension  being  reduced  suddenly 
by  withdrawal  into  the  condensing  human  body.  The  practical  moral 
of  this  experiment  is  to  always  keep  the  short-circuiting  key  closed  save 
exactly  when  the  induced  electricity  is  being  used,  thus  avoiding  ex- 
plosions of  the  sort  demonstrated. 


Fig.  275 


Fig.  276 


Effect  on  the  contraction  of  much  increasing 
the  load.  Each  curve  from  left  to  right  repre- 
sents fifty  grams  more  load  beginning  with  tlie 
lever's  weight  only.  Frog's  gastrocnemius. 
Intervals  of  about  forty-five  seconds. 


Effect  on  the  contraction  of  increasing 
the  load.  Each  curve  from  left  to  right  rep- 
resents ten  grams  more  load  beginning  with 
tlie  lever's  weight  only.  Frog's  gastrocne- 
mius.   Intervals  of  about  forty-five  seconds. 


The  theory  of  unipolar  induction  is  practically  given  in  the  direc- 
tions for  the  experiment;  induced  electricity  wlien  allowed  to  accumulate 
on  one  secondary-coil  pole  has  a  high  tension  and  the  consequent 
ability  to  jump  through  considerable  spaces  of  non-conductors.  In 
practical  neurology,  for  example,  in  testing  muscles  for  reaction  in  cases 
of  disease,  this  principle  is  of  great  importance,  and  errors  of  diagnosis 
may  be  easily  made  by  disregarding  it. 

Expt.  .54. — Influence  of  Load  on  Contraction. — (Apparatus:  Myo- 
graph, inductorium,  sartorius,  various  weights.)  Set  up  the  apparatus 
for  making  myograms  from  the  .sartorius  muscle,  used  in  place  of  the 
gastrocnemius.  Use  maximal  break  induction-shocks,  cutting  out 
all  the  makes.     With  the  drum  stationary,  record  a  contraction  when 


THE  PHYSIOLOGY  OF  MUSCLE  495 

the  muscle  is  loaded  witli  a  scale-pan  only.  Turn  the  drum  (by  hand) 
1  mm.  Add  1  gm.  to  the  scale-pan  and  stimulate  exactly  as  before. 
Continue  thus,  adding  a  gram  each  time  until  the  load  is  10  gm.  Then 
add  5  gm.  before  each  stimulation  and  record,  and  continue  until  the 
muscle  no  longer  contracts  (1000  grams?).  Observe  (a)  the  increase 
in  the  contraction's  height  by  a  moderate  load,  and  (6)  the  decrease  as 
the  loads  are  further  increased.  (Figure  out  the  power-index  of  the 
muscle,  keeping  its  bipenniform  shape  in  mind.) 

This  is  further  evidence  of  the  important  principle  that  a  muscle  works 
best  under  normal  conditions.  The  average  resistance  to  contraction 
is  one  of  these  conditions,  here  represented  by  weights.  When  a  muscle 
attempts  to  contract  against  a  weight  which  it  cannot  at  all  lift,  it  is 
obvious  that  the  muscle  is  expending  much  energy,  as,  indeed,  might  be 
easily  demonstrated  by  calorimetric  measurements  of  the  heat,  water, 
carbon  dioxide,  and  nitrogen  excreted  and  of  the  oxygen  and  food  con- 
sumed. Hence  in  the  biological  definition  of  work  the  space  and  move- 
ments involved  are  of  a  minute  or  even  molecular  nature. 

Expt.  55. — Volume  of  Contracting  Muscles  Does  Not  Increase. — 
(Apparatus :  Volume-tube,  stand-rod,  etc.,  inductorium,  modified  Ringer's 
solution,  entire  leg  of  frog.)  Place  the  frog's  leg  in  the  tube  and  hook 
the  lower  electrode  into  one  end  of  it.  Fill  the  tube  quite  full  of  the 
Ringer's  fluid,  insert  the  rubber  stopper  and  hook  the  upper  electrode 
into  the  upper  end  of  the  mass  of  muscles,  being  careful  that  no  bubbles 
of  air  whatever  remain  in  the  tube.  Push  down  the  plunger-rod  until 
the  solution  rises  well  into  the  capillary.  Now  pass  a  maximal  alter- 
nating induction-current  through  the  leg,  making  it  contract  and  continue 
contracted.  The  liquid  does  not  rise  in  the  capillary  tube,  proving  that 
the  volume  does  not  increase  while  the  shape  changes.  Does  the  volume 
decrease  ? 

During  the  contraction  of  cross-striated  muscle  (Schafer)  the  sarcoplasm 
of  each  sarcomere  passes  into  the  longitudinal  canals  of  the  latter,  being 
stopped  by  the  transverse  Krause's  membrane  in  the  middle  of  each 
sarcomere.  Thus  the  fibril  is  thickened  and  shortened,  doing  its  part 
in  this  way  to  shorten  the  whole  muscle  and  so  to  approximate  its  ends. 

Expt.  56. — Effects  of  Heat  and  of  Cold  on  Contraction. — (x\pparatus: 
Muscle-cooler-and-heater,  myograph,  inductorium,  finely  cracked  ice, 
salt,  Bunsen  burner.)  Place  the  cooler-and-heater  on  a  stand-rod  high 
enough  so  that  the  lamp  or  burner  will  stand  far  beneath  the  side  tube. 
INIake  a  gastrocnemius  muscle  preparation,  place  the  femur  in  the  screw- 
clamp  inside  the  cover  of  the  cooler,  having  attached  a  fine  copper  wire  to 
the  tendo  Achillis.  Pass  the  end  of  this  wire  through  the  hole  in  the  bottom 
of  the  collar  and  attach  it  to  the  muscle-lever  in  the  usual  way,  arranged 
to  write  on  the  smoked  drum.  Fill  the  space  around  the  muscle-cham- 
ber solid  full  with  finely  cracked  ice  and  sprinkle  on  a  few  grams  of  salt 
before  covering.  When  the  temperature  has  reached  a  degree  or  two 
above  zero,  stimulate  the  muscle  with  a  single  maximal  break  induction 
shock  and  record  an  accompanying  time  line.     Have  the  drum  rotate  at 


496 


APPEXDIX 


a  medium  speed  and  keep  this  speed  throughout  the  experiment.  Make 
two  or  three  of  these  curves.  Now  Hght  the  gas-burner  (having  its 
smokeless  flame  not  over  3  cm.  high)  and  place  it  under  the  outer  end  of 
side-tube.  AVhen  the  temperature  has  risen  5°  cause  another  maximal 
break  shock  and  record  as  before.  Repeat  this  for  every  5°  rise  of 
temperature,  having  the  series  of  eight  or  nine  curves  all  on  one  drum. 
As  the  temperature  reaches  45°  the  muscle  begins  to  go  into  heat-rigor, 
as  is  shown  by  its  slight  irregular  contractions.  Now  have  the  drum 
revolve  at  a  slow  speed  so  as  to  obtain  a  graphic  record  of  this,  the  final 
dying  contraction  of  the  muscle,  above  the  abscissa  line. 

Fig.  277 


Apparatus  as  set  up  by  students  to  study  the  work  done  by  a  frog's  cross-striated  muscle. 


Compare  the  shape  of  the  various  curves  as  regards  (a)  the  decreasing 
lengths  of  the  latent  periods;  (h)  the  increasing  c|uickness  of  contraction; 
(c)  the  increasing  quickness  or  relaxation;  and  {d)  the  increasing  heights 
of  the  lever's  rise,  save  at  first,  until  near  the  end  when  the  extent  of  the 
contraction  somewhat  decreases  (as  also  the  relaxation)  as  the  muscle 
begins  to  stifl'en  with  the  heat. 

I'he  degree  of  heat  of  a  muscle  has  much  to  do  with  the  various 
analyzed  parts  of  the  contraction-movements.  (1)  The  latent-period 
is  shortened  by  increasing  the  temperature  up  to  about  35°,  it  being  per- 
haps half  as  long  as  at  5°.  (2)  In  general  terms,  the  amount  of  shorten- 
ing of  the  muscle  is  increased  by  the  iip])er  limit  of  heat  (as  shown  by 
height  of  the  myogram),  this  increase  l^eing  40  per  cent,  or  so  over  that 
of  the  muscle  at  5°.     (3)  Generally  speaking,  the  contraction  time  is 


THE  PHYSIOLOGY   OF  MUSCLE  497 

lessened,  the  time  of  55°  being  approximately  half  that  at  5°.  (4)  In- 
crease of  temperatnre  lessens  tiie  relaxation-period  of  the  muscle,  that 
at  30°  lieing  from  25  to  15  per  cent,  that  at  5°.  These  estimates  are  for 
the  gastrocnemius  of  the  frog,  and  apply  in  detail  to  no  other  muscle, 
and  even  here  are  not  at  all  constant. 

Expt.  57. — Work  Done  by  a  Muscle. — (Apparatus:  Work-adder, 
inductorium,  kymograph,  centimeter-rule.)  Arrange  the  gastrocnemius 
muscle  above  the  work-adder  so  that  the  lever  of  the  latter  will  write  on 
the  drum,  while  the  thread  with  50  gm.  on  its  end  hangs  over  the  edge 
of  the  table,  the  weight  nearly  on  the  floor.  Mark  with  ink  the  spot  on 
the  thread  at  the  top  of  the  base  of  the  work-adder.  Now  stimulate  the 
muscle  with  single  maximal  break  induction-shocks  (carefullv  cutting 
out  makes  as  usual)  every  three  seconds  by  the  watch.  Continue  this 
until  the  muscle  no  longer  moves  the  lever  or  winds  up  the  thread. 
Have  the  drum  rotate  slowly  so  that  the  myograms  shall  be  very  close 
together  and  all  on  one  line  around  the  drum.  ]\Iark  with  ink  the  thread 
(at  the  same  level  as  before)  at  the  end  of  the  muscle's  work.  Unwind 
the  thread  from  the  wheel  and  measure  the  distance  in  centimeters 
between  the  ink-marks.  This  number  multiplied  by  fifty  (grams  of 
weight  lifted)  gives  the  gram-centimeters  of  work  the  particular  muscle 
did  under  the  conditions  of  the  experiment.  Note  the  changing  height 
of  the  myograms,  and  the  shape  of  the  curve  connecting  their  summits. 

The  energy  of  muscle  is  derived  from  the  chemical  katabolism  of 
carbohydrates  (largely  glycogen),  fats,  and  proteids.  In  man  about  a 
third  may  be  given  out  as  muscular  work.  Fick  found  that  of  the  latent 
energy  in  a  muscle  resisted  by  a  heavy  load,  one-third  may  be  used  to 
lift  this  load,  while,  if  the  latter  be  light,  not  over  5  per  cent,  is  utilized 
mechanically,  the  muscle  then  working  at  a  disadvantage. 

A  heavily  loaded  muscle,  then,  does  more  work  than  one  lightly  loaded. 
With  70  gm.  load  the  work  done  may  be  nearly  ten  times  as  great  as  when 
the  load  was  5  gm.,  while  the  length  of  the  lift  may  be  much  less.  The 
muscles  of  homotherms  are  stronger  than  those  of  poikilotherms,  but  the 
muscles  of  insects  are  stronger  than  others  and  much  more  active  besides. 

Expt.  58. — The  Contraction-icave. — (Apparatus:  Two  muscle-levers, 
two  stand-rods,  cork  clamp,  femur-clamp,  inductorium,  kymograph, 
tuning-fork,  millimeter-rule).  Place  the  cork  clamp  horizontally  in  the 
femur-clamp;  arrange  the  muscle-levers,  one  on  each  stand-rod,  so  that 
the  cork  stilts  (previously  tied  on  under  the  levers)  may  rest  on  either 
side  of  the  muscle  on  the  glass  plate  of  the  cork  clamp,  and  both  write  on 
the  drum.  It  is  essential  that  a  line  connecting  the  writing-points  of  the 
levers  should  be  exactly  vertical,  else  measurement  of  the  speed  of  the 
waves  cannot  easily  be  made. 

Now  prepare  a  long  narrow  strip  of  muscle,  including  the  sartorius, 
from  the  thigh  of  the  frog,  and  place  it  under  the  cork  clamp  (which 
should  be  pressed  down  somewhat  lightly)  and  under  the  cork  stilts  of 
the  levers.  When  the  drum  is  rotating  at  its  maximum  speed,  stimulate 
one  end  of  the  muscle  with  one  maximal  break  induction-shock  (the 
32 


498  APPENDIX 

tuning-fork  also  writing  its  vibrations),  using  the  platinum  electrode. 
The  lever  nearer  the  electrode  will  be  pushed  upward  by  the  contraction 
wave  first,  and  the  other  lever  will  rise  a  few  hundredths  of  a  second 
later.  Drop  from  the  beginnings  of  the  two  myograms  perpendicular 
lines  to  the  tuning-fork's  record,  and  count  the  number  of  double  fork- 
vibrations  between  the  two  lines.  This  number  will  be  the  time  in 
hundredths  of  a  second  required  by  the  contraction-wave  to  travel  be- 
tween the  cork  stilts.  Measure  the  length  of  the  muscle  between  these 
two  points.  Reduce  these  millimeters  per  hundredths  of  a  second  to 
meters  per  second  and  the  result  is  the  speed  of  the  contraction-wave 
in  the  particular  case  studied. 

The  contraction-wave  is  to  be  discriminated  from  the  action-current. 
The  latter  is  electrical  and  perhaps  an  extraneous  phenomenon,  while 
the  contraction-wave  is  the  actual  physical  thickening  of  the  muscle 
which  progresses  in  the  likeness  of  a  wave  through  the  muscle  at  a 
definite  rate.  This  thickening  begins  at  any  point  in  a  muscle  where 
a  stimulus  is  applied  to  it,  and  divides  and  moves  in  both  directions  up 
and  dowTi  the  muscle.  It  progresses  at  the  rate  of  about  3  m.  per  second 
in  the  cross-striated  muscles  of  the  frog,  and  faster  in  those  of  homo- 
therms.  The  wave  is  about  30  cm.  long,  that  is,  were  a  muscle  long 
enough,  at  intervals  of  30  cm.  along  the  muscle  the  thickening  or  crest 
of  the  wave  would  be  seen  simultaneously.  In  the  red  cross-striated 
muscle  of  the  rabbit  Rollett  found  the  contraction-wave  rate  to  be  about 
3.4  m.,  but  in  the  white  fibers  it  may  go  as  fast  as  11  m.;  in  human  mus- 
cle the  speed  is  (Hermann)  from  10  to  13  m.  per  second.  This  pro- 
gressive wave  of  thickening  of  the  whole  muscle  is  of  course  dependent 
directly  on  the  thickening  of  the  individual  striped  fibers  in  the  well- 
known  way. 

In  smooth  muscle,  according  to  Engelmann,  the  rate  is  only  about 
0.025  m.  per  second,  while  in  the  frog's  heart  ventricle  (the  muscle 
being,  so  to  say,  intermediate  in  character)  the  rate  is  (Waller)  about 
0.1  m.  per  second. 

Expt.  59. — Polar  Siimulation. — (Apparatus:  Sartorius  muscle,  rheo- 
cord,  simple  key,  and  dry-cell.)  Slit  up  the  sartorius  about  one-third  its 
length  and  lay  it  on  the  glass  plate.  Have  the  plate  and  the  muscle 
comparatively  dry.  Place  the  anode  on  the  left-hand  side  of  the  muscle, 
the  cathode  on  the  right-hand  leg.  Close  the  key,  hold  it  three  seconds 
and  then  open  it.  On  the  make,  the  right  side  of  the  muscle  (cathode) 
contracts  and  on  the  break  the  left  (anode) — i.  e.,  application  of  a  mod- 
erate galvanic  current  causes  stimulation  at  the  cathode,  and  removal 
of  the  current  stimulation  at  the  anode. 

Expt.  00. — Phy.nolocjical  Anode  and  Cathode. — (Apparatus:  Rectus 
abdominis  muscle  of  frog,  rheocord,  simple  key,  and  dry-cell.)  Connect 
a  dry  cell  with  a  rheocord  and  key  in  the  usual  way.  Remove  the  rectus 
al)dominis  muscle  and  lay  it  well  stretched  out  longitudinally  on  the  glass 
plate  with  weiglits  if  necessary.  Place  the  anode  from  the  rheocord  on 
one  end  of  the  muscle  and  the  cathode  on  the  other.     Using  a  very  faint 


HE  ART -MUSCLE 


499 


current,  send  a  make-shock  of  galvanism  through  the  muscle.  At  the 
cathodal  end  of  each  compartment  of  the  muscle  a  fahit  contraction  will 
be  seen.  Open  the  key,  and  a  slight  contraction  will  be  seen  at  each 
anode.     The   muscle  as   a   whole  has   no  general   contraction.     This 


Fig.  278 


Sarcolemma 


Dc^yere's  hillock 


Nerve 
fibre 


■-''::.e?iiii#^ 


^  "  —  -*  ^  S"'        w 


-  *  5-* 


;#••« 


The  contraction-wave  in  cross-striated  muscle  (Cassida  eque.>tri.<).  The  beginning  of  the  con- 
traction-wave of  shortening  and  thickening  is  seen  at  the  left  in  thick  black  lines.  (RoUet  via 
SzjTnonowicz  and  MacCallum.) 

condition  suggests  the  facts  as  regards  the  number  of  physiological  anodes 
and  cathodes  in  any  part  of  the  body,  e.g.,  a  man's  arm  when  stimulated 
through  the  skin.  Subsidiary  anodes  and  cathodes  then  clinically  are 
apt  to  be  numerous  and  must  be  allowed  for. 


VII.     HEART-MUSCLE. 


Exyl.  61. — The  Stannius  Ligatures. — (Apparatus:  Kymograph,  etc., 
heart-lever,  frog-board,  needle  and  thread,  inductorium.)  (Cardiograph.) 
(A)  The  First  Ligature. — Having  pithed  a  large  frog  and  fastened 
it  to  the  frog-board,  open  slightly  the  thorax  and  expose  the  heart  by 
opening  the  pericardium.     Cut  the  connective  tissue  from  beneath,  lift 


500  APPENDIX 

up  the  heart,  pass  the  moistened  thread  under  the  bulbus  arteriosus 
(coming  from  the  ventricle)  and  around  over  the  two  superior  vense 
cava?,  carefully  avoiding  the  inclusion  of  the  aorta.  Tie  the  thread 
around  the  junction  of  the  sinus  venosus  and  the  right  auricle.  Draw 
the  ligature  with  a  surgeon's  hitch  just  tightly  enough  directly  over  the 
whitish  "crescent."  The  auricles  and  ventricles  after  a  movement  or 
two  T\ill  stop  beating,  although  the  sinus-venosus  continues.  Touch 
the  apex  gently  with  the  needle  and  observe  that  the  ventricles  may  be 
easily  artificially  stimulated  to  contract. 

{B)  The  Second  Ligature. — With  the  first  ligature  in  place,  tie  a  second 
bit  of  moist  thread  around  the  heart  in  the  auriculo-ventricular  groove 
just  above  the  ventricle.  When  properly  adjusted  just  over  Bidder's 
ganglion  (which  must  be  found  by  chance  more  or  less  in  these  small 
hearts),  the  heart  begins  again  its  automatic  rhythmic  beat,  but  at  a  rate 
slower  than  normal. 

These  two  experiments,  first  performed  by  Stannius  in  1851,  are  more 
easily  carried  out  successfully  than  certainly  explained.  The  cause  of 
the  phenomena  of  the  first  ligature  is  especially  obscure,  but  there  are 
two  tentative  explanations:  The  first  ligature  may  stimulate  the  inhibi- 
tory action  of  Remak's  ganglia  in  connection  with  the  vagus.  Another 
way  of  accounting  for  the  facts  of  the  first  ligature  is  that,  if  the  beat 
of  the  heart  originates,  as  is  generally  admitted,  in  the  sensitive  tissues 
of  the  sinus  venosus,  this  ligature  may  cut  off  the  progress  of  the  impulse, 
thus  making  necessary  a  long  pause  before  the  ventricle  can  gather 
energy  enough  to  make  a  beat  of  its  own  originating.  It  is  usually  con- 
sidered that  the  second  ligature  starts  up  the  heart  by  stimulating  Bidder's 
ganglion  in  the  auriculo-ventricular  septum,  and  that  this  constant 
stimulation  has  the  same  (trophic?)  influence  on  the  ventricle  as  has  the 
normal  influence  coming  to  this  ganglion. 

Expt.  62. — Every  Contraction  Maximal. — ("All  or  None.") — (Appara- 
tus: Kymograph,  inductorium,  heart-lever,  needle,  and  thread.)  Place 
about  under  the  bulbus  venosus  of  a  frog's  heart  the  first  ligature  of 
Stannius,  as  described  in  the  former  part  of  the  previous  experiment, 
bringing  thereby  the  heart  to  a  stand-still.  Put  the  pan  of  the  cardio- 
graph (heart-lever)  under  the  heart  without  detaching  the  latter  from  its 
anatomical  connections,  and  connect  witli  it  wires  from  the  secondary 
ccjil  of  the  inductorium  arranged  for  single  make  and  break  shocks. 
Place  the  secondary  coil  so  far  from  the  primary  that  neither  make  nor 
break  causes  the  apex  ('ventricle)  to  contract.  Arrange  the  lever  of  the 
cardiograph  for  writing  on  the  drum  while  the  latter  is  stationary. 
Move  the  secondary  coil  very  slowly  and  gradually  toward  the  primary 
until  a  single  break  shock  causes  contraction  of  the  apex.  Turn  the 
drum  a  millimeter  by  hand  and  stimulate  again  with  a  make-shock. 
Now  gradually  increase  the  strength  of  the  stimulus  and  make  a  record 
each  time  (allowing  at  least  thirty  seconds  to  elapse  l)etween  each  two) 
until  the  shocks  are  of  maximal  strength.  Comparing  the  height  of 
the  cardiograms,  it  will  be  seen  that  the  last  is  not  lf)nger  than  the  first. 


HEART-MUSCLE  501 

In  other  words,  the  heart  contracts  on  the  principle  of  "all  or  none." 
The  aluminum  heart-lever  may  be  used  instead  of  the  older  heart-pan; 
the  platinum  electrode  is  then  applied  directly  to  the  suspended  heart. 

As  has  been  learned  in  the  work  on  cross-striated  nuiscle,  the  force  of 
its  contraction  varies  somewhat  with  the  stimulus;  but  the  heart,  as  we 
see,  does  not  beat  on  this  principle.  It  is  impossible  to  be  sure  as  yet 
why  this  is  so.  Gaskell,  one  of  the  leading  authorities  on  cardiac  contrac- 
tion, thinks  this  phenomenon  (and  also  that  of  the  refractory  period  and 
the  fact  that  the  heart  cannot  easily  be  tetanized)  may  be  explained  by 
supposing  that  in  case  of  the  heart  all  the  heart-cells  are  stimulated 
together  by  even  a  weak  stimulus;  or  (on  the  supposition  that  the 
metabolism,  both  up-and-down,  of  the  heart  is  slower  than  that  of 
■cross-striated  muscle  and  the  energy-material  more  stable),  that  they 
are  less  easily  katabolized  in  contraction.  (See  also  notes  at  end  of  the 
directions  for  Expt.  67.) 

Expt.  63. — Muscular  " Aufomaticity." — ("  Engelmann's  Incisions.") 
(Apparatus:  Fine  scissors  and  a  frog.)  Expose  the  heart  of  the  pithed 
frog;  lift  it  gently  by  the  lower  end  of  the  apex,  and  with  a  pair  of  small, 
sharp-pointed  scissors  make  transverse  incisions  into  the  ventricles  from 
both  sides,  so  that  those  from  each  side  extend  beyond  the  middle  line 
but  do  not  connect.  By  these  means  any  nerves  which  might  extend 
from  base  to  apex  might  be  cut.  Observe  that  the  contraction-wave 
passes  over  the  slashed  ventricle  down  the  zigzag  strip  of  muscle  from 
base  to  apex. 

This  "  automaticity"  of  certain  muscular  tissue  is  a  large  question, 
which  becomes  more  complicated  rather  than  simpler.  It  is  essentially 
the  problem  whether  muscle  can  act  normally  without  any  mfluence 
from  nerves  so  long  as  it  is  supplied  with  nutriment  and  kept  in  physio- 
logical condition.  It  involves,  too,  the  whole  matter  of  the  general  func- 
tion of  the  nervous  system.  Lately  the  ions  and  the  theory  of  the  electro- 
lytic dissociation  of  inorganic  salines  have  come  into  the  problem. 
Discussion  of  the  matter  is  out  of  the  question  here,  but  see  the  theo- 
retical notes  of  Expts.  67  and  68,  and  the  discussion  in  the  body  of 
the  book,  page  29.3,  etc. 

Expt.  64. — The  Inherent  Beat-rhythm. — (Apparatus:  Dry-cell,  rheo- 
cord,  stand-rod,  femur-clamp,  key,  wires,  dissecting-plate.)  Connect 
the  rheocord  to  a  cell  through  a  key.  From  the  block  and  anodal  post 
of  the  rheocord  run  wires  to  the  jaws  of  the  clamp  so  that  their  ends 
may  be  applied  to  the  heart  in  a  fixed  position,  the  hands  not  being  steady 
enough  (do  not  twist  the  wires  together).  Sever  the  ventricles  of  a  frog's 
heart  carefully  at  the  auriculo-ventricular  groove,  lay  them  on  the  glass 
plate,  and  keep  them  only  barely  moist  with  saline.  This  isolated 
^'apex"  does  not  beat.  Now  stimulate  it  (one  electrode  on  each  side) 
with  the  constant  galvanic  current,  gradually  increasing  its  strength 
until  the  make  just  causes  a  contraction.  At  this  istrength  let  the  current 
pass  continuously  through  the  apex.  It  will  beat  rhythmically,  such 
beinff  its  life-habit  and  that  of  its  cardiac  ancestors. 


502 


APPENDIX 


From  some  source  (perhaps  from  a  progressive  anabolism  in  the 
protoplasm,  possibly  from  the  nervous  system),  the  normally  beating 
heart  receives  a  constant  stimulation.  The  galvanic  current  may 
serve  as  a  substitute  for  the  normal  stimulus  v^^hatever  it  is,  and  occa- 
sion similar  reaction.  Other  muscle  does  the  same,  for  example  the 
ureter,  the  dartos,  and  in  some  cases  the  intestinal  muscle. 

Expt.  65. — No  Cardiac  Tetanus? — (Apparatus:  Needle,  thread, 
inductorium,  key,  kymograph,  etc.,  heart-lever.)  Apply  the  first 
Stannius  ligature  (around  under  the  sinus  venosus)  as  described  in 
Expt.  61.  Place  the  quiet  heart  in  the  heart-lever,  connect  the  latter 
with  the  inductorium  arranged  for  tetanizing  currents  (with  the  armature 
vibrating),  and  arrange  the  lever  to  write  on  a  slowly  rotating  drum. 
Stimulate  the  heart  with  three  strengths  of  this  alternating  current, 
weak,  medium,  and  maximal,  each  for  a  series  of  ten  or  more  beats. 
Xothine:  like  the  tetanus-curve  of  cross-striated  or  of  smooth  muscle  is 
produced. 

.    Fig.  279 


lllllllimilllll  IIIIIIIIMIIII  MUM 


Normal   frog-cardiogram  by  the  suspension-method, 
read  from  left  to  right.      Original  size. 


The  auricular   beat  occurs  first. 
The  time-line  is  in  seconds. 


To  be 


If  the  frog's  heart,  however,  be  warmed  to  35°  and  such  a  current  be 
sent  through  the  heart,  something  approaching  tetanus  is  produced  in 
the  organ.  This  is  thought  to  be  abnormal;  it  is  perhaps  a  degree  of  the 
torpidity  due  to  heat  rigor,  or  to  the  coagulative  death  of  the  cardiac 
protoplasm.     The  matter,  however,  needs  further  study. 

Expt.  66. — Temperature  Affects  Contraction. — (Apparatus:  Heart- 
lever,  kymograph,  chronograph,  etc.,  Ringer's  fluid  at  3°  and  at  about 
40°,  pipets.) 

{A)  Put  the  normal  heart  in  connection  with  the  heart-lever  and  make 
a  series  of  cardiograms  on  a  drum  rotating  slowly;  by  a  watch  make  on 
the  curve  a  short  mark  exactly  every  ten  seconds,  or  use  the  time-marker. 
This  record  shows  the  rate  of  the  heart  at  a  room  temperature,  about 
18°.     Determine  exactly  this  rate  per  minute. 

(B)  Start  a  cardiogram  on  a  lower  drum-level.  With  a  large  pipet 
drop  by  drop  add  the  modified  cold  Ringer's  solution  to  the  heart. 
r)l).serve  that  the  heart  at  once  slows.  Measure  off  the  cardiogram 
into  ten-second  periods  as  before,  and  calcutate  the  cold  pulse-rate  per 
minute,  and  the  percentage  of  retardation. 


HEART-MUSCLE 


503 


(C)  Again  push  the  (h-uin  down  so  that  the  lever  may  write  in  a  fresh 
place  just  above  tlie  normal  curve.  With  the  pipet  add  a  few  centi- 
meters of  the  Ringer's  solution  at  30°.  The  heart  soon  heats  much 
more  rapdily.  ^Measure  oft'  the  record  and  count  the  beats  per  minute. 
(If  the  degree  of  heat  be  as  high  as  35°,  the  ventricle  ceases  while  the 
auricle  continues;  a  few  degrees  warmer,  and  the  heart  muscle  dies  in 
heat-rigor.)  Calculate  the  rate  and  percentage  of  change  as  before. 
(See  Fig.  153,  page  286.) 

There  is  little  that  needs  general  explanation  in  these  results.  Almost 
universally  does  protoplasm  slow  its  action  when  cold  and  hasten  it 
when  warmed  to  a  degree  somewhat  below  that  of  its  coagulative  death. 
Poikilothermous  animals  show  this  better  than  homothermous  animals 

Fig.  280 


Apparatus  as  set  up  by  students  to  prove  the  action  of  electrolytic  salines  on  the 
frog's  heart-muscle. 


could,  for  their  tissues  are  adapted  to  these  changes.  The  heart  of  a 
frog  buried  in  the  mud  at  the  bottom  of  a  cold  pool  probably  does  not 
beat  fully  all  winter,  but  only  hard  enough  to  maintain  a  very  sluggish 
circulation.  The  same  sort  of  cardiac  acceleration  obtains  in  persons 
when  they  have  a  fever;  that  is,  a  relatively  slight  rise  of  body-tempera- 
ture. In  Daphnia  the  changes  are  much  more  marked  than  in  the  frog. 
We  saw  the  ameba  hasten  its  streaming  movements  when  it  was  warmed; 
when  in  the  water  near  the  freezing-point  it  is  apparently  but  a  tiny  drop 
of  almost  motionless  colloid. 

Expt.  67. — The  Importance  of  {Electrolytic f)  Salines. — Perfusion  with 
Ringer's  Solution. —  (Apparatus:    Heart-oncometer,   Ringer's  solution.) 


504  APPEXDIX 

Tie  a  piece  of  the  thinnest  rubber  dam  over  the  top  of  the  arm  of  the 
oncometer,  and  fill  it  with  Ringer's  fluid  (consisting  of  a  weak  solution 
of  sodium  and  potassium  chlorides  and  of  basic  calcium  phosphate  in 
distilled  water).  Remove  a  large  frog's  heart  by  cutting  it  transversely 
with  the  scissors  about  midway  through  the  auricles.  With  a  moistened 
fine  silk  thread  tie  the  heart  over  the  end  of  the  perfusion  cannula  so  that 
the  latter  shall  extend  just  into  the  ventricle  through  the  auriculo- 
ventricular  opening,  and  be  sure  that  the  openings  of  the  cannula  are  not 
obstructed.  Press  the  cork  of  the  cannula  into  the  body  of  the  oncometer 
and  adjust ,  if  necessary,  so  that  the  heart  shall  hang  free  in  the  surround- 
ing solution,  being  sure  that  the  instrument  contains  no  bubble  of  air. 
Fill  the  portion  of  the  inflow-tube  above  the  closed  clamp  with  the  solution, 
and  insert  the  short  arm  of  the  siphon  in  the  Ringer's  fluid  in  the  beaker 
above.  Adjust  to  the  rubber  diaphragm  the  tiny  cork  block  and  above  it 
the  light  straw  lever  attached  to  the  cork  stopper  by  a  crank-shaped  pin. 
Now  loosen  the  pinch-cock  slightly  to  allow  the  solution  to  run  slowly 
down  the  tube.  Gradually  raise  the  upper  beaker  in  the  stand-ring. 
Wlien  the  pressure  has  reached  that  of  10  or  15  cm.  of  water  the  ventricle 
will  }>egin  to  beat  rhythmically.  If  not,  insert  fine  copper  wires  in  the 
oncometer  and  connect  them  with  a  dry-cell  through  a  key.  It  is  some- 
times impossible  to  obtain  frog-hearts  large  enough  for  this  experiment; 
it  is  difficult  to  insert  the  perfusion-cannula  into  the  ventricle  of  a  small 
frog-heart  without  obstructing  the  former. 

Only  in  very  recent  years  has  the  extreme  importance  of  the  salines 
in  the  blood  become  apparent,  but  calcium,  magnesium,  sodium,  potas- 
sium, etc.,  are  now  known  to  be  important  in  the  composition  of  proto- 
plasm. Deprived  of  their  continual  supply  of  these  metals  by  way  of 
the  }>lood,  tissues  promptly  cease  to  function,  while,  on  the  other  hand, 
an  isolated  heart  even  of  a  mammal  may  be  made  to  beat  for  hours  when 
perfused  with  these  salines  in  the  proper  proportions  and  kept  warm 
and  moist.  We  are  still  only  at  the  gate-way  of  the  physiology  of  the 
inorganic  salts  in  protoplasm.  Perhaps  the  ions  are  the  real  causes  of 
this  complex  influence  of  the  various  saline  substances. 

Expt.  68. — The  Refractory  Period, Extra  Contraction,  and  Compensatory 
Pause. — (Apparatus:  Kymograph,  etc.,  heart-lever,  inductorium,  heart.) 
Place  the  normal  heart  in  the  heart-lever  and  arrange  the  latter  to  write 
on  the  drum  rotating  at  a  slow  speed.  Ilun  wires  to  the  heart  from  the 
inrluctorium's  secondary  coil.  Record  the  normal  beat  of  the  heart  on 
the  drum.  liarly  in  the  uprise  of  the  lever  at  some  beat  throw  into  the 
heart  a  maximal  make  induction-shock  (cutting  out  the  break).  By 
stimulation  within  this  ])eriod  no  extra  contraction  is  produced.  This 
(the  j)erir)d  of  systole  af)proximately)  is  the  ''refractory  period^'  of  the 
heart.  Throw  in  another  maximal  make-shock  just  at  the  height  of 
the  lever's  rise;  the  stimulation  now  causes  an  extra  beat.  This  is 
the  "extra  contraction.^'  Now  observe  that  the  next  automatic  beat 
does  not  occur  at  the  time  in  the  regular  rhythm  when  it  should,  but  that 
there  is  a  jjansc  <if  the  heart  until  the  time  of  the  succeeding  regular  beat. 


HEART-MUSCLE  505 

This  is  the  "compensatory  pause."  In  other  words,  the  rhythm  of  the 
beat  is  not  (Hsturbahle  during  systole,  but  when  disturbed  at  any  other 
time  the  inherent  rhythm  is  maintained  by  a  pause  of  just  the  right 
length  so  that  the  next  beat  occurs  in  the  regular  rhythm. 

All  the  metabolic  processes  of  cardiac  muscle  probably  take  place 
more  slowly  than  do  those  in  cross-striated  muscle.  It  is  on  this  account 
perhaps  that  the  heart's  refractory  period  is  so  long;  that  the  viscus  can- 
not easily  be  tetanized;  and  that  there  is  no  relation  l)etween  the  power 
of  the  beat  and  the  strength  of  the  stimulus  (Gaskell).  The  cause  of  the 
refractory  period  is  probably,  in  fine,  then,  the  absence  during  that  time 
of  energy  sufficient  to  allow  of  a  contraction,  the  immediate  supply  of 
power  having  been  used  up  by  the  systole.  Indeed,  according  to  Engle- 
mann,  the  power  of  responding  to  very  weak  stimuli  is  regained  only  at 
the  end  of  the  following  rest  (diastole).  Cross-striated  muscle,  however, 
has  a  refractory  period,  although  it  is  much  shorter  than  the  heart's. 

The  compensatory  pause  means  that  when  the  rhythm  is  disturbed  by 
an  extra  beat  the  heart  cannot  contract  for  a  long  period  again  because 
the  energy  is  used  up;  it  takes  up,  however,  the  rhythm  inherent  in  the 
muscle  and  beats  at  the  time  this  rhythm  requires. 

The  extra  contraction  during  the  systolic  period  is  nowise  imlike 
that  occasioned  by  a  stimulus  applied  to  a  cross-striated  muscle,  there 
being  now  nothing  to  prevent  this  contraction,  for  the  heart  has  now 
again  an  adequate  supply  of  energy. 

Expt.  69. — The  Action-current  Precedes  the  Beat. — (Apparatus: 
Heart-lever,  kymograph,  etc.,  myograph,  counterpoise  for  heart-lever.) 
Smoke  a  drum  lightly,  and  weight  the  short  arm  of  the  heart-lever  so 
that  it  is  nearly  as  heavy  as  the  long  arm.  Set  the  cardiograph  on  the 
base  of  the  stand-rod  and  arrange  the  gastrocnemius  muscle  in  the  femur- 
clamp,  etc.,  above  it  in  the  ordinary  way  save  that  the  lever  is  above  the 
femur-clamp.  (Use  the  pulley  on  the  muscle-lever  so  that  on  contraction 
the  muscle  pulls  the  lever  upward  as  usual,  and  not  dow^lward,  although 
below  the  lever.)  Adjust  the  femur-clamp  to  the  cardiograph  so  that  the 
nerve  of  the  nerve-muscle  preparation  shall  rest  longitudinally  on  the 
heart.  Arrange  the  two  levers  to  write  exactly  over  each  other  on  the 
slowly  rotating  drum.  At  each  beat  of  the  heart  the  sciatic  nerve  will 
be  stimulated  and  the  gastrocnemius  will  contract.  Note  that  the  cross- 
striated  muscle's  record  begins  at  each  beat  before  the  heart's  record 
begins.  Apply  a  tuning-fork  and  try  to  measure  the  length  of  time  by 
which  the  action-current  anticipates  the  actual  action  of  the  heart.  (To 
insure  prompt  success  in  this  experiment  the  gastrocnemius  and  sciatic 
must  be  freshly  prepared  and  very  sensitive.  The  result,  when  obtained, 
is  striking.) 

It  has  been  already  shown  (Expt.  50)  that  when  a  skeletal  muscle 
contracts  its  action-current  is  an  adequate  stimulus  to  muscle  like  any 
other  electric  current  of  sufficient  energy.  It  is  easier  to  show  the  pre- 
cedence of  this  action  current  on  the  heart  which  beats  "automatically." 

The  impulse  occasioning  the  beat  starts  at  the  central  end  of  the  large 


506  APPENDIX 

veins  and  proceeds  quickly  over  the  heart,  the  connection  between  the 
auricles  and  the  ventricle  being  made  not  by  nerves,  but  by  a  few  slender 
fibers  of  muscle  extending  from  the  auricles  to  the  ventricle.  The  speed 
of  this  contraction-impulse  (mechanical)  is  great,  but  very  much  less  than 
that  of  the  (electrical)  action-current.  Indeed,  the  contraction  of  the 
heart,  including  its  brief  latent-period,  requires  so  relatively  long  that  not 
only  the  heart's  action-current  passes,  but  it  has  time  to  stimulate  a  nerve 
and  produce  contraction  in  a  skeletal  muscle  before  the  heart's  contrac- 
tion occurs.  The  difficulty  of  the  experiment  is  due  to  the  trouble  of 
placing  the  nerve  so  as  to  receive  well  the  heart's  action-current.  A  lack 
of  sensitivity  in  the  nerve  and  muscle  used  prevents  a  good  result. 

Expt.  70. — Polar  Inhibition. — (Apparatus:  Flat  electrode,  cell, 
rheocord,  commutator,  key,  fine  copper  wire).  With  one  rheocord- 
pole  connect  the  flat  electrode  and  with  the  other  the  piece  of  fine  wire. 
Cut  off  the  upper  jaw  of  a  frog  and  expose  the  heart.  Place  the  flat  brass 
electrode  in  the  mouth  of  the  frog  and  the  end  of  the  fine  wire  on  the 
beating  ventricle.  Observe  closely  the  heart-tissue  under  the  end  of  the 
fine  wire,  and  with  the  commutator  rocked  so  that  the  end  of  the  wire  is 
the  anode,  close  and  hold  the  key.  During  systole  it  is  clear  that  con- 
traction does  not  occur  at  this  point,  for  the  tissue  remains  red  and  does 
not  pale  like  the  remainder  of  the  heart.  This  is  the  active  inhibitory 
effect.  Now  shift  the  rocker  of  the  commutator  so  that  the  fine  wire- 
point  becomes  the  cathode,  and  close  the  key  again.  The  effect  now 
occurs  during  diastole:  the  spot  remains  pale  while  the  apex  relaxes, 
indicating  that  the  cathodal  stimulation  inhibits  normal  relaxation. 

The  results  of  this  experiment  must  be  taken  at  present  empirically — 
they  cannot  be  definitely  and  certainly  explained.  When  a  weak  current 
goes  through  the  heart  the  anodal  pole  causes  inhibition  of  contraction 
at  that  point,  while  if  the  cathodal  pole  be  on  the  heart,  concentrated 
in  space,  a  local  inhibition  or  relaxation  occurs.  There  have  been  two 
theories  of  explanation  of  inhibition  in  general — one  that  it  is  purely  a 
nervous  effect,  and  the  other,  more  probable,  that  the  influence  arises  in 
the  muscle  or  gland  directly.  On  the  latter  hypothesis  the  inhibitory 
influence  comes  from  a  cessation  of  katabolism,  activity  involving  katab- 
olism  as  surely  as  rest  gives  rise  to  the  anabolic  process.  The  former  is 
usually  obvious,  but  the  anabolic  process,  giving  little  sign,  may  be  hard  to 
appreciate.  Gaskell  goes  so  far  as  to  say  that  the  inhibitory  influence 
probably  .sets  up  active  anabolism,  which  thereupon  checks  katabolism. 
This  is  called  the  trophic  theory  of  inhibition.  There  is  at  present, 
however,  no  surety  that  these  two  opposed  processes  may  not  go  on 
simultaneously  in  a  tissue.  Inhibition  is  a  subject  of  great  promise 
to  researchers  into  the  basal  relationship  of  the  tissues  and  the  nervous 
system. 

Expt.  71. —  Tonus. —  (Apparatus:  Kymograph,  etc.,  muscle-lever, 
tortoise.)  Chop  off  a  tortoise's  head  and  saw  ofl'  the  lower  part  of  the 
.shell.  Pass  a  fine  wire  through  the  auricle  of  the  tortoise's  isolated  heart 
and  connect  it  with  the  muscle-lever,  arranged  to  write  on  the  slowly 


HEART-MUSCLE  ,107 

rotating  tlriira.  Note  the  compound  cardiogram,  the  hirger  waves  repre- 
senting the  tonus  of  the  heart  and  the  smaller  vibrations  the  beats. 
From  ten  to  forty  of  the  latter  occur  during  one  tonus-wave.  This 
phenomenon  appears  to  be  widespread  if  not  universal  in  muscle,  but 
its  import  is  not  yet  clear.  Under  certain  conditions  not  yet  definable 
these  vasomotor  tonal  changes  occur  also  in  the  frog's  heart.  (See 
Figs.  157  and  100.) 

Expt.  72. — Muscarine  and  Atropine  (its  antidote). — (Apparatus :  Heart- 
lever,  inductorium  with  platinum  electrodes,  muscarine-solution,  atropine- 
solution,  frog  or  tortoise.)  Set  up  the  inductorium  for  alternating  cur- 
rents. Expose  the  heart,  and  stimulate  the  pale  "crescent"  (between  the 
sinus  venosus  and  right  auricle)  with  strong  alternating  currents.  The 
heart's  beat  is  more  or  less  inhibited.  Now,  with  a  pipet  add  three  drops 
or  so  of  the  muscarine-solution  to  the  heart.  It  gradually  comes  to  a 
standstill.  Stimulate  the  ventricle  with  induction-shocks  and  observe 
how  little  irritable  the  muscle  is.  Let  it  alone  a  few  minutes.  Now  let 
fall  a  few  drops  of  the  atropine-solution  on  the  heart.  It  gradually  beats 
again,  perhaps  more  powerfully  than  is  normal.  Stimulate  the  crescent 
as  before.  No  inhibition  now  takes  place,  for  the  atropine  has  paralyzed 
the  neural  mechanism  of  the  heart. 

Muscarine  is  the  alkaloid  which  sometimes  kills  people  who  eat  poi- 
sonous fungi.  As  in  this  experiment,  its  action  is  directly  on  the  heart- 
muscle  and  not  on  the  cardiac  nerve-mechanism.  Atropine,  then,  is  the 
physiological  and  therapeutic  antidote  of  muscarine,  but  it  acts  powerfully 
on  the  nerve-cells  in  the  heart.  As  these  are  of  inhibitory  function  (see 
Expts.  61  and  87),  no  harm  follows.  It  acts  also  on  the  muscular  tissue 
and  it  is  here  that  it  exerts  its  direct  antagonism  to  the  muscarine. 

Expt.  73. — Nicotine. — (Apparatus:  Kymograph,  etc.,  heart-lever, 
pipet,  0.1  per  cent,  nicotine-solution,  frog,  and  Daphnia).  Expose  the 
heart  and  make  record  of  its  beat  on  the  rotating  drum.  Now  add  a  few 
drops  of  the  weak  nicotine-solution.  The  heart  slows  for  a  short  time 
and  then  beats  more  strongly  than  before.  The  slowing  is  due  to  a 
stimulation  of  the  intracardiac  inhibitory  mechanism,  while  the  aug- 
mentation of  the  beat  comes  from  a  partial  paralysis  of  the  same  nerve- 
cells.  Nicotine  in  small  quantity  stimulates  and  then  paralyzes  the  neu- 
rones, especially  the  cell-bodies. 

Nicotine  for  some,  probably  chemical,  reason  has  a  predilection  for  the 
cell-bodies  of  the  neurones,  exerting  no  effect  on  the  neuraxones.  Exces- 
sive smoking  has  on  the  human  heart  some  of  this  demonstrated  effect, 
making  it  irregular  and  rapid.  The  stimulating  result  of  the  four  to- 
bacco alkaloids  is  seen  in  their  action  on  the  cerebral  cortex:  they  incite 
to  mental  work  and  abolish  to  a  marked  degree  the  feeling  of  fatigue. 
Their  action,  however,  on  the  nerve-cells  of  the  walls  of  the  stomach  is 
often  disastrous  to  perfect  digestion.  (See  page  169.)  Demonstration 
of  nicotine's  action  on  the  heart  of  Daphnia  (see  Expt.  12). 

Expt.  74. — Adrenalin. — (Apparatus:  Cardiograph,  0.01  per  cent,  solu- 
tion of  adrenalin  chloride  in  Ringer's  solution,  frog's  heart.)     Make  a 


50S 


APPEXDIX 


normal  car(lio<]:vam  as  before.  Bathe  the  heart  with  the  solution  drop 
by  drop  and  record  tlie  beats  just  above  the  normal  curve,  all  conditions 
else  remaining  constant.  Note  the  actions  of  the  adrenalin  on  the  pulse- 
rate  and  on  the  power  of  contraction,  and  how  systole  and  diastole  are 
each  affected. 

Expf.  75. — Carbon  Dioxide,  Oxygen,  Ether,  Chloroform,  Nitrous 
Oxide,  Carbon  Monoxide,  Ammonia. — (Apparatus:  Thistle-tube  gas- 
chamber,  femur-clamp,  heart-lever,  kymograph,  extra  stand-rod,  wire, 
thread,  frog's  heart,  vapors,  and  bulb  for  infusing  the  same.)  Arrange 
the  thistle-tube  in  the  femur-clamp  directly  over  the  long  arm  of  the 
heart-lever.  Excise  the  frog's  heart,  leaving  the  great  vessels  long. 
Pass  the  wire  hook  of  the  gas-chamber  stopper  through  the  little  mass  of 
the  vessels.     Pass  a  thread  with  a  small  wire  hook  on  its  upper  end  down 

Fig.  281 


Apparatus  as  set  up  by  students  to  show  the  action  of  various  vapors  on  the  frog's 

heart-muscle. 


thrf)Ugh  the  glass  tube  and  fasten  to  the  long  arm  of  heart-lever  near  the 
fulcrum.  Insert  the  wire  hook  tii rough  the  ventricle  not  too  near  the 
apex.  Place  the  stopper  in  position  and  adjust  the  fine  wire  through  it 
so  that  the  beating  heart  at  each  shortening  will  lift  the  lever. 

By  means  of  the  bulb-infuser  blow  a  small  amount  of  a  vapor  into  the 
ga.s-chamber  and  close  the  openings  of  the  latter. 

Record  these  drug-cardiograms  and  compare  them  with  the  normal 
curve.  After  each  experiment  thoroughly  wash  the  heart  with  Ringer's 
fluid  and  allow  it  to  rest  a  short  time. 

Ex-pt.  76. — Lymph-hearts. — (Apparatus:  Frog  (or  tortoise  or  snake), 
frog-boards,  seeker,  watch).  V'xih  the  frog's  brain  and  fasten  the  animal 
belly-down  on  the  frog-board,  the  hind  legs  abducted.  By  sliort  trans- 
verse gentle  incisions  jast  above  the  pyramidalis  muscle  near  the  end  of 


NERVE 


509 


the  urostyle  open  into  the  small  triangular  spaces  on  either  side  of  the 
latter.     A  small  transparent  lymph-heart  will  be  seen  in  each  space. 

[A)  Count  the  number  of  their  pulsations  per  minute,  and  compare 
their  rhythm  with  that  of  the  blood-heart.     Do  they  correspond? 

(B)  Pith  the  caudal  part  of  the  spinal  cord  and  observe  that  the  beat- 
ings of  these  lymph-hearts  stops,  while  the  blood-heart  is  undisturbed. 

Fig.  2S2 


Apparatus  as  set  up  by  students  to  compare  the  beat-rhythms  of  the  blood-heart  and  of 
the  lymph-hearts  in  the  frog. 

By  boring  a  hole  through  the  frog-board  the  beat  of  the  blood-heart 
may  be  recorded  on  the  drum,  the  connecting  thread  passing  over  the 
requisite  pulleys.  With  a  Morse  key  arranged  to  actuate  a  signal  writing 
just  under  the  pen  of  the  heart-lever,  the  time  of  the  pulsations  of  the 
lymph-hearts  may  also  be  recorded.  By  this  simple  means  the  com- 
parison may  be  made  directly  in  a  graphic  way  and  many  altering  condi- 
tions of  the  lymph-heart  rate  may  be  studied. 


VIII.     NERVE. 


Very  great  care  must  be  observed  in  experiments  on  nerves  that  they 
be  uninjured  by  mechanical  or  chemical  influences.  Drying  (chemical 
injury)  is  especially  to  be  guarded  against,  and  to  prevent  it  a  nerve 
should  never  be  allowed  to  hang  free  in  the  open  air.  In  all  experi- 
ments requiring  more  than  a  few  minutes  the  moist-chamber,  lined  more 
or  less  with  salined  filter-paper,  should  be  used.  However  inconvenient, 
these  protectors  from  evaporation  are  essential  in  experimental  work  on 
isolated  nerves. 


510  APPENDIX 

Expt.  77. — Neuraxones  Conduct  in  Both  Directions. — (Apparatus: 
Cell,  inductorium,  key,  sartorius.)  Isolate  the  sartorius  muscle  carefully 
and  place  it  on  the  dried  dissectmg-plate.  The  motor  neuraxones  in  this 
muscle  divide,  one  part  going  to  each  side  of  the  lower  end.  Slit  up  the 
middle  line  one-third  of  the  broad  end  of  the  muscle,  and  stimulate  with 
the  smallest  strength  of  break  induction-shock  that  will  cause  a  contrac- 
tion on  one  "leg"  of  the  divided  muscle,  both  electrodes  being  at  the  end 
of  the  other  leg.  Observe  that  with  this  stimulus,  or  one  slightly  stronger, 
contraction  takes  place  in  the  other  leg  of  the  muscle  also.  The  efferent 
neuraxones  have  conducted  impulses  afferently  as  well  as  efferently. 

Another  place  besides  the  sartorius  muscle  that  this  principle  may  be 
demonstrated  is  on  the  nerves  supplying  the  electrical  organ  of  the  electric 
catfish  (Malapterurus),  where  a  single  neuraxone  supplies  a  large  organ 
that  may  be  detached  from  the  fish  completely,  and  its  nerve  studied. 

Expt.  78. — Effect  Depends  on  Connections. — (Apparatus:  Inductorium, 
key,  frog-board.)  Pith  the  brain  only  of  a  frog  and  place  the  animal 
belly  do^^^l  on  the  frog-board.  Cut  out  and  away  the  upper  third  of  the 
spinal  column  (which  extends  from  the  head  only  to  the  urostyle).  With 
fine  and  small  scissors  cut  away  the  bone  at  either  side  of  the  remainder 
of  the  spinal  cord  (l^eing  very  careful  not  to  injure  in  any  way  the  latter), 
thus  having  the  cord  free  of  its  vertebral  bony  covering.  Observe  the 
posterior  (afferent)  roots  and  the  large  anterior  (efferent  or  motor)  roots 
lying  beneath  them. 

(.4)  Afferent  Fibers  not  Motor. — ^Tie  a  ligature  about  the  largest  posterior 
root  close  to  the  cord  and  cut  the  root  between  these.  Stimulate  with 
very  weak  single  induction-shocks  the  peripheral  portion  of  the  divided 
root.  Practically  no  leg  movements  occur.  The  posterior  roots  are 
afferent. 

(B)  Afferent  Fibers  Connect  with  Motor  Neurones. — ^Tie  a  ligature  about 
another  of  the  large  posterior  roots  as  far  as  possible  from  the  cord, 
cutting  the  root  peripherally  to  the  ligature.  Gently  stimulate  the  central 
portion.     Muscular  contractions  occur. 

(C)  Anterior  Roots  not  Afferent. — Cut  through  all  the  posterior  roots  of 
the  side  on  which  Expt.  B  was  performed.  Stimulate  mechanically  and 
chemically  the  skin  of  the  leg  on  the  same  side.  No  movements  occur. 
Stimulate  similarly  the  other  leg.     Movements  occur  in  both  legs. 

iD)  Efferent  Fibers  Motor. — Ligate  a  large  anterior  root  close  to  the 
cord  ancj  sever,  as  l)efore,  between  the  ligature  and  cord.  Stimulate  the 
peripheral  cut  end.  Contractions  occur  in  the  muscles  attached.  The 
stimuli  must  be  very  weak. 

(F,)  Efferent  Fibers  do  not  Conduct  Centrally  to  Motor  Neurones. — ^Tie 
another  anterior  root  far  from  cord,  and  cut  peripherally  to  the  ligature. 
Stimulate  as  before  near  the  central  cut  end.     No  movements  follow. 

(F)  Cut  all  the  remaining  anterior  roots,  and  stimulate  mechanically 
and  chemically  the  skin  of  the  legs.  Now  no  contractions  whatever  occur, 
all  the  central  connections  being  cut. 

No  spinal  root,  however,  is  purely  either  afferent  or  efferent. 


NERVE 


511 


Expt.  79. — Speed  of  the  Nervous  Impulse. — (Apparatus:  Kymograph, 
etc.  (myograph),  glass  nerve-plate,  tuning-fork,  electro-magnetic  signal, 
commutator,  millimeter-rule.)  Twist  around  each  end  of  the  dry  glass 
nerve-plate  two  fine  wires  3  mm.  apart,  and  connect  their  ends  with  the 
four  binding-posts  of  the  commutator  without  its  cross-wires.  Connect 
the  rocker-posts  with  the  secondary  coil  of  the  inductorium.  Arrange 
tlie  myograph  to  write  on  the  drum,  the  nerve-plate  close  to  the  top  of  the 
gastrocnemius,  the  signal  (and  the  key)  in  the  primary  circuit  of  the 
inductorium  writing  directly  and  exactly  under  the  pen  of  the  myo- 
graph's  lever.  Hold  the  tuning-fork  so  that  it  will  write  under  the  signal. 
Make  a  gastrocnemius  preparation,  having  the  nerve  as  long  and  normal 
as  possible.     Lay  the  nerve  on  the  glass  nerve-holder  over  the  two  pairs 


Fig.  283 


Apparatus  as  arranged  by  students  to  show  the  speed  of  the  nervous  impulse  in  the 

frog's  sciatic. 


of  electrodes,  one  pair  near  the  muscle,  the  other  at  the  nerve's  end.  Rock 
the  commutator  so  that  the  shock  will  enter  the  nerve  by  the  pair  of 
electrodes  nearer  the  muscle.  When  the  drum  is  spinning  (raised  by  the 
top  screw  from  its  friction-bearing)  set  the  tuning-fork  vibrating  and 
stimulate  the  nerves  with  a  moderate  break-shock  (cutting  out  the  make). 
Now  lower  the  drum  to  a  fresh  place.  Shift  the  rocker  so  the  current 
may  go  in  by  the  further  pair  of  electrodes  and  make  a  similar  curve  with 
a  break-shock,  making  the  time-record  also.  The  time-interval  between 
stimulation  and  the  beginning  of  the  myogram  (as  showTi  by  the  tuning- 
fork)  will  be  less  in  the  former  curve  than  in  the  latter.  Count  the 
difference  in  hundredths  of  a  second.  This  is  the  time  required  for  the 
nervous  impulse  to  pass  between  the  two  pairs  of  electrodes.  Measure 
this  distance  in  millimeters  and  calculate  the  speed  in  meters  per 
second. 


512  APPEXDIX 

It  was  the  great  Helmholtz  who  first  noticed  that  nervous  impulses 
require  time  for  their  transmission,  and  he  demonstrated  it  on  the  sciatic 
of  the  frog  and  on  man.  Time  is  required  because  the  setting-up  of 
chemical  (or  electrical  or  molecular)  change  in  the  millions  of  complex 
molecules  along  the  progress  of  the  impulse  takes  time.  The  actual  rate 
varies  widely  in  the  different  nerves  of  different  animals,  but  along  the 
frog's  sciatic  (poikilothermous  mixed  nerve)  the  rate  in  the  winter-season 
is  usually  20  meters  per  second.  It  is  often  much  less.  In  sensory  nerves 
it  is  apparently  about  the  same.  In  man  the  average  rate  is  not  far 
from  40  meters  per  second. 

Some  of  the  conditions  which  decrease  the  speed  are  the  dying  degenera- 
tion of  the  nerve,  cold,  pressure,  stretching,  fatigue,  alcohol,  ether,  and 
strong  electricity.     Heat  increases  the  rate. 

Expt.  SO. — Electrotonus. — (Apparatus:  Dry-cell,  key,  commutator 
with  cross-wires,  myograph,  glass  nerve-plate,  15  per  cent,  sodium- 
chloride  solution,  fine  copper  wires.)  Twist  two  copper  wires  4  cm.  apart 
about  the  glass  nerve-plate  and  connect  their  ends  with  two  adjacent 
posts  of  the  commutator  with  cross-wires.  Connect  the  rocker-posts 
with  a  dry-cell  through  the  key.  Adjust  the  nerve-plate  close  to  top  of 
gastrocnemius  in  the  myograph  so  that  its  long  and  normal  nerve  will  lie 
over  the  electrodes. 

{A)  Anelectrotonus. — Between  the  electrodes  and  1  cm.  from  that  nearer 
the  muscle,  place  on  the  nerve  a  single  drop  of  the  sodium-chloride 
solution.  Rock  the  commutator  so  that  the  nearer  electrode  shall  be  the 
anode.  Observe  the  irregular  contractions  due  to  the  chemical  stimula- 
tion bv  the  chlorine.  Now  close  the  key.  The  contractions  lessen  or 
cease.  Anelectrotonus  is  in  this  case  a  condition  of  lessened  irritability. 
Sometimes  it  is  not  so. 

(B)  Cateledrotonus. — Now  shift  the  rocker  so  that  it  is  the  cathode 
that  is  nearer  the  strong  salt  solution,  and  close  the  key.  The  irregular 
contractions  of  the  muscle  occasioned  by  the  salt  are  much  increased. 
Catelectrotonus  is  a  condition  of  increased  irritability. 

Expts.  59,  60,  and  70  suggest  the  same  fact  that  this  experiment 
demonstrates. 

Gotch  thus  summarizes  Pfluger's  general  conclusions  as  to  electrotonus, 
which,  as  its  name  implies,  is  only  a  condition  of  irritability  or  tone 
caused  in  a  nerve  by  a  stimulus:  "Under  tlie  influence  of  a  constant 
current  flowing  through  a  nerve  there  is  an  increase  in  the  nerve-excita- 
bilitv,  at  or  near  the  negative  pole  (cathode),  a  decrease  at  or  near  the 
positive  pole  (anode).  On  the  cessation  of  the  current  these  changes 
are  reversed,  the  cathode  being  the  seat  of  the  fall,  and  the  anode  that  of 
a  rise  in  excitability.  Tlie  aherations  in  excitability  are  most  intense 
at  the  poles,  but  spread,  diminishing  with  the  distance,  into  the  intra- 
polar  and  extrapolar  regions.  At  some  point  in  the  intrapolar  region 
the  boundary  between  the  two  polar  extensif)ns  is  reached;  this  point  is 
therefore  unaft'ected,  and  is  termed  tlie  in<hf}"erence-point.  The  excita- 
bihtv  changes  are  true  for  all  forms  of  stimulation,  electrical,  mechanical, 


NERVE  513 

or  clieniical,  and  for  both  efferent  and  afferent  nerves."  The  conchtion 
is  explainal)le  at  present  only  tentatively;  the  most  likely  theory,  perhaps, 
is  that  of  electrolytic  changes  by  the  ions  of  the  nerve-protoplasm,  about 
which  little  is  as  yet  definitely  known. 

Expt.  81. — Afferent  Impulses  may  Inhibit  Reflexions. — (Apparatus: 
Stand-rod  with  femur-clamp,  inductorium,  key,  0.5  per  cent,  sulphuric 
acid,  acetic  acid,  beakers,  small  rubber  rings.)  (A  and  B  of  Expt.  78, 
as  well  as  many  other  experiments,  indirectly  indicate  the  nature  and 
neural  mechanism  of  reflexions.) 

(A)  Observe  that  a  normal  frog  placed  on  its  back  immediately  re- 
turns, thus  restoring  its  normal  equilibrium.  Now  put  a  rubV^er  ring 
about  the  proximal  part  of  one  fore-leg.  The  animal  no  longer  rights 
its  position,  nor  does  the  unconstricted  leg  show  any  tendency  toward 
moving  for  that  purpose.  This  shows  that  the  effect  is  in  the  nervous 
system  and  not  in  the  muscles.  This  inhibitory  influence  lasts  only 
about  fifteen  minutes,  the  reflex  mechanism  for  maintaining  equilibrium 
then  becoming  tolerant  of  the  unusual  stimulus.  In  a  decerebrated 
frog  the  returning-reflex  is  too  much  deranged  to  be  effective. 

{B)  Pith  the  brain  of  the  frog  and  hang  up  the  animal  by  the  lower 
jaw  in  the  clamp.  Lower  one  foot  into  the  beaker  containing  a  little 
sulphuric  acid  and  with  a  watch  carefully  measure  the  time  (reflex 
reaction-time)  until  the  leg  is  withdra\\ai.  Wash  off  the  acid  carefully 
with  water  and  repeat  the  experiment.  Wash  off  the  acid  again,  and  so 
on  ten  times.  Average  the  reaction-times.  Again  immerse  a  foot  and 
stimulate  the  other  with  a  strong  alternating  induction-current,  holding 
the  foot  down  for  the  purpose.  The  reflex  reaction-time  of  the  leg 
irritated  by  the  acid  will  be  greatly  lengthened  or  perhaps  so  strongly 
influenced  that  the  leg  is  not  withdrawn  at  all,  inhibition  being  com- 
plete. 

Expt.  82. — Vaso-motor  Function  of  Cord. — (Apparatus:  Stand-rod, 
femur-clamp,  and  seeker.)  Pith  the  brain  only  of  a  frog.  Make  a 
small  incision  in  the  abdomen  and  draw  out  a  loop  of  intestine;  expose 
the  heart.  Observe  these  two  organs  with  respect  to  the  amount  of  blood 
in  each,  noting  especially  the  hardness  of  the  heart  during  systole  and 
the  size  of  the  blood-vessels  of  the  gut  and  omentum.  Now  carefully 
with  a  blunt  wire  seeker  pith  the  cord  of  the  frog.  Note  that  the  blood 
now  collects  in  the  easily  distensible  omentum. 

The  cord's  vaso-motor  centers  are  normally  subordinate  to  centers 
in  the  medulla  oblongata,  for  when  the  local  centers  of  the  cord  and 
sympathetic  ganglia  are  cut  off  from  the  bulb  (medulla)  many  days 
are  necessary  before  the  local  centers  in  the  cord  by  themselves  take  up 
complete  control.  The  neuraxones  of  probably  all  the  spinal  vaso-motor 
cells  end  in  sympathetic  ganglia  (Langley).  Sometimes  these  cells  give 
out  rhythmic  impulses  to  the  arterioles  under  their  control.  The  vaso- 
motor centers  can  be  stimulated  reflexly  from  the  blood-vessels,  from  the 
afferent  nerves  generally,  or  from  the  emotional  centers  probably  in  the 
optic  thalamus.  There  is  an  inverse  relation  between  the  surface  vaso- 
3.3 


514  APPEXDIX 

motor  nerves  and  those  of  the  viscera,  as  is  seen  cHnieally  oftentimes  in 
congestions  from  exposure  to  external  cold. 

In  this  experiment  as  carried  out  here  all  vaso-motor  control  of  the 
viscera  is  destroyed  and  the  main  bulk  of  the  blood  collects  where  the 
force  of  gravitation  draws  it. 

Expt.  S3. — Xcuraxoncs  Praciically  Uiifaiiguahle. — (iVpparatus: 
iNIoist-chamber,  inductorium,  two  dry-cells,  platinum  electrodes,  myo- 
graph, keys.)  Arrange  the  gastrocnemius  nerve-muscle  preparation  in 
the  moist-chamber  in  connection  with  the  muscle-lever  below  and  place 
the  end  of  the  long  nerve  on  the  platinum  electrode  connected  w^ith  the 
secondary  coil  of  the  inductorium  arranged  through  a  key  for  tetanizing 
currents.  On  the  nerve  between  this  stimulating  electrode  and  the 
muscle  place  two  fine  wire  non-polarizable  electrodes  so  that  there  will 
be  a  descending  current  connected  with  the  other  dry-cell  through  a  key. 
Observe  that  the  muscle  contracts  when  stimulated  with  the  induction- 
shocks.  Throw  through  the  nerve  the  galvanic  constant  current,  and 
while  it  is  passing  stimulate  again.  No  contraction  now  occurs,  for  the 
constant  current  acts  as  a  "block"  to  the  transmission  of  the  stimulus 
by  lowering  the  irritability  of  the  neuraxones.  Now  leaving  the  galvanic 
current  running,  stimulate  the  nerve  continuously  for  a  long  time  with 
the  rapidly  tiring  tetanizing  current.  Such  stimulation  would  fatigue 
the  "muscle"  quickly,  but  the  galvanic  block  prevents  this,  although  not 
preventing  active  stimulation  of  the  nerve  between  the  platinum  electrodes 
and  the  "block."  After  long  stimulation  shut  off  the  galvanic  current, 
thus  removing  the  block,  and  short-circuit  the  induction  current.  Now 
open  the  short-circuiting  key,  thus  again  stimulating  the  muscle  through 
the  nerve.  The  muscle  contracts  quite  as  well  as  if  the  nerve  had  been 
unstimulated. 

It  cannot  be  surely  said  that  neuraxones  are  theoretically,  that  is 
absolutely,  unfatiguable,  for  it  is  inconceivable  that  a  form  of  protoplasm 
so  delicate  and  elaborate  chemically  as  is  nerve  should  not  suffer  from 
exhaustion  of  its  stored  energy,  whatever  it  is,  when  continuously  dra"WTi 
upon  for  very  long  periods.  There  is  a  normal  balance  between  ana- 
holism  and  katabolism  which  must  be  disturbable  after  a  time.  The 
functioning  of  nerve  may  be,  however,  sufficiently  intermittent  to  allow 
of  apparently  continuous  performance,  just  as  the  heart  seemingly  works 
continufMisly.  In  reality,  as  we  know,  it  rests  three-quarters  of  the  time, 
and  only  for  this  reason  needs  no  long  periods  of  rest. 

Nerve-cells  are  fatigued  with  comparative  ease,  as  was  shown  by  Hodge. 
He  kept  sparrows  flying  continuously  for  many  hours,  and  then  compared 
their  cortical  motor  cells  with  those  of  sparrows  which  had  been  at  rest. 
The  changes  both  in  the  cytoplasm  and  the  nuclei  were  very  striking,  both 
being  much  shrunken.     (See  Fig.  27.) 

Expt.  84. — The  Influence  of  Strychnine. — (Apparatus:  Pipet,  0.5  per 
cent,  solution  of  strychnine,  seeker.)  Pith  the  brain  f)rily  of  a  frog.  Into 
one  of  the  lymph-sinuses  lying  on  either  side  of  the  sjMual  column  inject 
a  single  drop  of  the  strychnine-solution  with  the  pipet.     In  a  few  minutes 


NERVE 


515 


spasms  of  the  leg-muscles,  etc.,  will  he  seen,  increasing  in  force.  Soon 
the  extensor  muscles  l)egin  to  overcome  the  flexors,  and  shortly  the  legs 
are  rigidlv  straight.  Note  the  extreme  irritability  of  the  whole  animal 
(due  to  abnormal  stimulation  of  the  cord  by  the  alkaloid):  asHgiit  pinch 
of  the  skin  causes  universal  con\Tilsions.  Now  destroy  carefully  with 
the  seeker  the  spinal  cord,  and  note  that  the  previously  noted  phenomena 
cease  at  once.     Strychnine  acts  on  the  spinal  cord  alone. 

The  precise  mode  of  action  chemically  of  strychnine  on  the  nerve-cells 
is  unknown,  but  whatever  it  may  be,  the  drug  collects  especially  in  the 
spinal  cord,  and  violently  stimulates  the  reflex  motor  nerve  cells.  Any 
influence  which  can  disturb  the  equilibrium  of  these  centers,  then,  causes 
strong  tonic  spasm  (contraction)  of  the  muscles.  It  is  apparently  wholly 
owing  to  the  fact  that  the  extensor  muscles  are  more  powerful  than  the 
flexors  that  the  resulting  position  of  the  animal  is  one  of  extreme  extension. 
The  practical  importance  of  acquaintance  with  the  phenomena  of  strych- 
nine-poisoning should  not  be  lost  sight  of. 

Fig.  284 


I  I  I  I  I  I  I  I  I  I  I  I  1  I  I  I  I  M  I  I  I  I  I  I  M  I  I  I  I  I  I  I  I  I  I  I  !  I  I  I  I  I  I  I  I  I  1  I  I  I  I  I  I  I  I  I  I  I  I  I  I  I  I  I  M 

Stimulation  of  the  uncut  vago-sympathetic  in  the  frog.  The  weak  stimulation  lasted  between 
the  little  squares  on  the  stimulation-line,  and  the  effect  took  place  only  about  twelve  seconds 
later.      To  be  read  from  left  to  right.      The  time-line  is  in  seconds. 


Expt.  85. — Augmentation  of  Function. — (Apparatus:  Frog-board,  in- 
ductorium,  shielded  stimulating  electrode,  heart-lever,  kymograph,  chro- 
nograph, etc.,  signal.)  One  of  the  best  examples  of  neural  augmentation 
is  the  effect  of  the  sympathetic  on  the  heart.  To  expose  the  sympathetic 
nerves  which  influence  the  frog's  heart,  pith  a  frog's  or  toad's  brain, 
fasten  the  animal  on  the  frog-board,  cut  away  the  lower  jaw  completely, 
and  excise  it  below  the  angles.  Very  carefully  remove  tissue  until  the 
upper  part  of  the  spinal  column  is  completely  bared.  Now  very  care- 
fully raise  and  cut  through  the  flat  strip  of  muscle  (the  levator  anguli 
scapulae)  extending  obliquely  outward  from  the  occipital  bone.  This 
exposes  the  vago-sympathetic,  the  vagal  ganglion,  and  the  sympathetic 
line  extending  upward  from  the  second,  third,  fourth,  and  fifth  vertebrae. 
(This  ascending  trunk  is  usually  pigmented  and  accompanied  by  an 
artery.)  Ligate  the  nerve  as  low  as  possible  and  cut  it  below  the  ligature. 
Keep  the  nerves  moist  with  modified  Ringer's  fluid.  Expose  the  heart 
and  place  it  in  the  heart-lever  arranged  to  write  on  the  very  slowly  rotating 
drum.     (The  writing  end  of  the  lever  should  ordinarilv  move  at  least 


516 


APPENDIX 


2  cm.)  If  the  heart  beats  rapidly,  slow  it  with  cold  solution.  Record 
the  normal  beat,  and  mark  ott'  exact  ten-second  periods,  or  use  a  time- 
marker.  After  twenty  contractions  or  so,  stimulate  the  sympathetic 
(already  ligated  and  cut)  above  the  ligature  with  a  weak  tetanizing 
current  of  induced  electricity.  Count  again  the  number  of  beats  in  ten- 
second  intervals  and  compute  the  percentage  of  the  acceleration  over  the 
normal  rate. 

In  the  frog  the  augmentor  impulses  leave  the  cord  by  the  third  spinal 
nerves,  go  by  the  communicating  branch  into  the  third  sympathetic 
ganglion,  up  the  sympathetic  chain  to  the  vagal  ganglion,  and  down  the 
trunk  of  the  vagus. 

The  ordinary  acceleration  from  stimulation  of  these  nerves  is  very 
variable  (10  per  cent,  or  several  times  that),  the  acceleration  being 
greater  when  the  heart  is  already  beating  slowly;  it  is  also  influenced  by 
the  length  of  time  the  stimulation  is  continued.  Excitation  of  the  nerves 
in  both  sides  at  once  accelerates  no  more  than  stimulation  of  only  one 
nerve.  The  speed  of  the  stimulation-wave  passing  over  the  heart  muscle 
is  increased.     (See  also  Chapter  VIII.) 


Fig.  285 


Stimulation  of  the  peripheral  stump  of  the  vago-sympathetic  in  tlie  frog.  The  stimulus  was 
an  alternating  induced  current  fairly  .strong,  and  its  time-relation.s  are  shown  by  the  middle  line. 
Note  the  gradual  acceleration  of  the  rhythm  as  the  inhibitory  influence  passed  away  from 
the  heart-muscle.      To  be  read  from  left  to  right.      Tne  time-line  is  in  seconds. 


Expt.  SO. — Inhibition  of  Function. — (Apparatus:  Frog-board,  small 
test-tube,  heart  lever,  inductorium,  chronograph,  signal,  kymograph.) 
Pith  the  brain  only  of  a  frog  and  fasten  the  body,  backdown,  on  the  frog- 
board.  Expose  the  heart  by  the  removal  of  the  sternum  and  draw  the 
forelegs  far  apart.  Pu.sh  the  test-tube  down  the  esophagus  to  distend 
the  ti.ssues  of  the  region.  Carefully  remove  the  muscles  lying  between 
the  angle  f)f  the  jaw  and  the  hyoid  bone  in  the  median  line.  C)l)serve 
the  three  fine  nerves  which  pass  upward  from  the  angle  of  the  jaw  be- 
tween the  flat  muscles;  the  lowest  of  these  is  the  hypoglossal,  next  is 
the  vagus  accompanied  by  a  bloo(l-ve.ssel,and  still  farther  forward  is  the 
glo.sso-j)liaryiigeal.  This  "vagus"  trunk  is,  of  course,  really  the  vago- 
sympathetic. 

Divide  the  glo.sso-phorvngeal  branch  of  the  vagus  trunk  to  prevent 
disturbing  contraction  of  the  muscles.     Place  the  heart  in  the  heart- 


NERVE  517 

lever  and  arrange  to  write  on  a  slowly  rotating  drum.  Place  protected 
electrodes  from  the  seconflary  coil  of  the  inductorium  under  the  vpgal 
trunk  and  remove  the  coil  from  the  primary.  Have  the  signal  in  the 
primary  circuit.  Record  a  normal  cardiogram,  marking  off  exact  ten- 
second  intervals.  Now  throw  a  weak  alternating  induction-current 
through  the  electrodes,  the  signal  marking  the  instant  of  stimulation. 
The  heart,  after  a  latent  period,  stops  in  diastole.  Note  the  length  of  the 
latent  period,  and  of  the  straight  inhibition-line  made  by  the  heart- 
lever.  The  viscus  soon  begins  to  slowly  beat  again  and  increases  its 
rate  even  though  the  alternating  current  be  continued.  The  inhibitory 
influence  then  is  not  complete,  but  only  of  a  directing  nature.  Measure 
the  period  of  inhibition. 

Repeat  this  procedure  with  an  induction-current  stronger  than  the 
one  already  used,  then  with  a  weaker  one.  The  mode  of  inhibition  will 
vary  according  to  the  conditions.  Observe  that  on  resuming  the  beat, 
the  sinus  venosus  always  begins  first  and  the  ventricle  last. 

The  six  sorts  of  effect  due  to  stimulation  of  the  frog's  cardiac  inhibitory 
nerves  have  been  already  given  in  Chapter  VIII  (see  page  295) . 

Expt.  87. — The  Intracardiac  Inhibitory  Mechanism. — (Apparatus: 
Frog-board,  inductorium,  platinum  electrode.)  Pith  a  frog's  brain. 
Expose  the  heart  and  lift  it  up  over  with  a  glass  rod.  Find  the  whitish 
crescent-shaped  spot  between  the  sinus  venosus  and  the  right  auricle. 
Here  are  situated  the  nerve-cells  connected  with  the  vagus.  Stimulate 
this  "crescent"  with  the  platinum  electrode  from  the  secondary  coil  of 
an  inductorium  arranged  for  alternating  currents.  After  a  beat  or  two 
the  heart  stops,  but  soon  begins  again  despite  continued  stimulation. 

These  nerve-cells  (Remak's  ganglion)  situated  in  the  crescent  are  the 
inhibitory  efferent  nerve-cells;  the  corresponding  efferent  augmentor 
cells  are  in  the  ganglia  on  the  spinal  roots — part  of  the  "sympathetic 
system."  They  are  probably  the  trophic  centers  of  the  heart  in  so  far 
as  they  determine  the  well-being  of  the  fibers  passing  from  them  to  the 
cardiac  muscle-tissue,  for  in  a  sense  the  well-being  of  any  part  depends 
on  the  efferent  fibers  coming  to  its  tissue.  The  nerve-cells  in  this  gang- 
lion have  one,  two,  or  many  poles;  some  of  the  unipolar  cells  in  the  frog's 
septum  have  peculiarities,  namely,  "a  spherical  form,  a  pericellular  net- 
work, and  two  processes" — the  axis-cylinder  and  the  spiral  process 
wound  about  the  former.  It  is  probable  that  this  spiral  process  and 
the  pericellular  net  but  not  the  axis-cylinder  are  in  connection  with  the 
vagus.     (Retzius  and  Nikola  jew). 

Expt.  64  demonstrated  that  the  frog's  heart  apex  containing  no  obvious 
ganglion-cells  could  beat  rhythmically.  Perhaps  then  the  inhibition 
by  these  nerve-cells  of  Remak's  ganglia  is  due  to  their  quasi-trophic 
influence  over  the  heart's  protoplasm.     The  matter  is  not  certain. 

Expt.  SS. — Functions  of  the  Hemispheres. — (Apparatus:  Decapitated 
frog,  sink  full  of  cool  water.)  The  frog,  as  given  out,  has  had  only  the 
cerebral  hemispheres  and  the  olfactory  lobes  anterior  to  them  removed, 
the  optic  thalami,  cerebellum,  medulla  oblongata,  and  cord  being  struc- 


518  APPENDIX 

turally  normal.  In  an  lioiir  or  less  the  nervous  shock  of  the  operation 
passes  oft'  and  the  functions  of  the  hemispheres  may  be  demonstrated  by 
noting  what  the  hemisphereless  frog  does  not  and  cannot  do  that  the 
normal  animal  does 

{A)  Shock. — Note  the  characteristics  of  the  nervous  shock  of  the  opera- 
tion :  the  entire  lack  of  muscular  tone,  etc.  (B)  Muscular  Action  and 
Posture  not  Disturbed.  Wait  until  the  shock  has  passed  off  (doing 
some  other  experiment  meanwhile).  The  heart-beat,  respiratory  move- 
ments, intestinal  peristalsis,  etc.,  continue  and  the  eyes  are  open  (and 
probably  seeing,  although  the  frog  does  not  recognize  objects).  The 
skeletal  muscles  have  recovered  their  tone  and  the  posture  of  the  animal 
is  nearly  or  quite  normal  (the  cerebellum  and  cord  remain).  (C)  Spon- 
taneity Lost.  Note  that,  unstimulated,  the  frog  does  not  move.  Were 
it  quite  unstimulated,  the  animal  would  die  of  thirst,  hunger,  or  drying 
without  changing  its  position;  intelligence  as  conceptualization  is  entirely 
lacking.  (See  Chapter  XII.,  page  416.)  (D)  Equilihrium  Maintained. 
The  frog  will  not  remain  in  a  supine  position.  If  placed  on  the  back  of  a 
hand  that  is  then  slowly  turned  over,  the  animal  keeps  its  equilibrium 
by  the  appropriate  complex  movements,  and  does  not  fall  oft'.  The 
optic  thalami  remain,  but  spontaneous  movement  is  never  made:  there 
is  no  deliberate  will.  {E)  Vision  Unimpaired.  Place  some  small  opaque 
object  (such  as  a  dissecting-case  on  end)  in  front  of  the  frog  on  the  table, 
and  pinch  a  hind  foot.  The  animal  jumps,  but  the  object  is  avoided. 
(F)  Biological  Reflexes  Persist.  In  water  deep  enough,  swimming  is  per- 
fectly carried  out,  and  the  frog  may  even  climb  on  the  rim  of  the  tank  and 
sit  there.  The  sexual  embrace  is  unimpaired.  Food  put  in  the  mouth 
is  swallowed.  (G)  Intelligence  Gone.  However  much  irritated,  the  frog 
does  not  hide  as  a  normal  frog  would  do,  but  jumps  only  once  or  twice 
and  then  sits  quietly  again.  Every  sort  of  recognition  is  gone  with  the 
fusion-processes  of  the  cortex  cerebri.  The  animal  sees  the  danger,  food, 
water,  etc.,  but  not  recognizing  what  they  are,  cannot  make  the  appro- 
priate actions. 


IX.  GALVANOTAXIS  AND  CHEMOTAXIS. 

Expt.  89. — Galvanotaxis. — (A})paratus:  Frog-tadpoles,  wax,  glass 
dissecting-plate,  two  dry-cells,  key,  commutator  with  cross-wires,  stand- 
rod,  femur-clamp,  0.1  per  cent,  sodium-chloride  solution.)  Make  a 
wax  trough  about  G  cm.  long,  2  cm.  wide,  and  1  cm.  deep  on  the  glass 
dissecting-plate  and  have  it  carefully  water-tight.  Fill  with  the  solution 
of  sodium  chloride.  Place  within  it  seven  or  more  frog-tadpoles  not  over 
2  cm.  long.  Clamp  the  wires  from  the  commutator  (with  cross-wires) 
in  the  femur  clamp  in  such  a  way  that  an  end  of  one  may  be  in  the  saline 
at  each  end  of  the  trough.  Determine  which  pole  is  now  the  anode  and 
close  the  key  so  that  three  volts  may  pass  through  tlic  liquid.  A  majority 
of  the  tadpoles,  after  being  .shaken  up,  collect  about  the  cathode.    Reverse 


GALVAXOTAXIS  AXD  CHEMOTAXIS  519 

the  current  by  shifting  the  rocker;  the  animals  again  turn  into  hne  with 
the  stream  and  generally  collect  about  the  cathode.  This  may  be 
repeated  a  few  times,  but  after  a  time  a  toleration  of  the  stimulus  sets 
up  in  the  tadpole  and  the  reaction  is  less  certain.  A  young  crayfish  works 
more  regularly  than  does  a  frog-tadpole  in  the  reaction  to  galvanism. 

The  various  tropisms  or  taxes  (of  which  galvano-tropism  or  galvano- 
taxis  is  only  an  example)  are  the  reactions  which  plant-protoplasm  and 
little-differentiated  animal  protoplasm  exhibit  when  subjected  unilaterally 
to  various  external  natural  influences.  Besides  reacting  to  galvanism, 
such  protoplasm  reacts  among  other  things  to  light  (phototaxis),  to  heat 
(thermotaxis),  to  chemicals  (chemotaxis),  to  pressure  (barotaxis,  of 
which  the  reaction  to  contract  with  solid  bodies,  thigmotaxis,  is  a  sub- 
division). One  sees  phototaxis  in  many  infusoria,  as  also  in  plants  when 
the  leaves  twist  around  to  face  the  light.  It  is  supposed  that  it  is  by  the 
force  of  chemotaxis  that  the  spermatozoa  are  attracted  to  the  ova.  Thig- 
motaxis is  well  seen  in  the  twining  of  the  tendrils  of  many  vines  about  a 
small  support.     (See  Verworn.) 

Explanation  of  these  reactions  as  a  whole  is  difficult  and  at  present 
doubtful  in  most  cases.  One  has  to  say  that  they  depend  on  inherent 
properties  of  protoplasm  acquired  for  their  usefulness.  Some  of  the 
reactions  can  be  explained  on  purely  physical  and  chemical  principles. 

Jennings  has  studied  these  interesting  phenomena  in  Paramecium 
with  great  industry  and  some  explanatory  success.  The  simpler  the 
organism  the  more  constant  the  reaction,  for  the  individual  will  is  least 
powerful  in  the  lowest  forms  of  life.  On  this  principle  even  young 
frog-tadpoles  show  a  less  uniform  reaction  than  would,  e.  g.,  paramecia 
or  amebse;  dogs  or  men  might  exliibit  none. 

Expt.  90. — Chemotaxis. — (x\pparatus:  Pure  culture  of  Paramecia, 
wide  slide,  large  cover-glass,  wires,  fine  pipet,  carbon  dioxide.)  Place  a 
large  drop  of  the  water  containing  the  paramecia  in  the  middle  of  the 
slide,  and  put  wires  about  3  cm.  apart  across  the  slide  on  either  side  of 
the  drop.  Place  a  cover-glass  on  the  water  and  see  that  the  latter  fills 
as  much  of  the  space  as  possible.  Observe  with  the  naked  eye  or  with 
the  biconvex  lens  that  the  infusoria  are  evenly  distributed  through  the 
water.  Now  with  the  pipet  force  a  single  small  bul^ble  of  air  under  the 
cover-glass,  and  then,  at  least  a  centimeter  away,  a  tiny  bubble  of  carbon 
dioxide.  The  paramecia  soon  congregate  in  a  ring  about  the  carbon 
dioxide.  This  genus  of  animal,  then,  is  positively  chemotactic  to  weak 
carbonic  acid,  as  it  is  to  most  other  acids  (Jennings).  As  the  gas  more 
and  more  dissolves  in  the  water,  its  solution  becomes  stronger  and  the 
animals  soon  move  away  from  it — i.  e.,  they  are  negatively  chemotactic 
to  strong  carbonic  acid. 

It  is  this  sort  of  attraction  perhaps  which  causes  the  spermatozoa  to 
enter  the  ovum,  being  aided  in  their  ascent  of  the  tubes  possibly  by 
another  sort  of  taxis,  rheotaxis,  or  reaction  against  the  current  of  lymph 
setting  toward  the  uterus. 


520 


APPEXDIX 


X.     OPTICS. 

Demonstration  of  the  artificial  eye  and  the  electric  lantern,  including 
its  lenses,  used  to  illustrate  it.  Complete  diagrams  of  all  the  optical 
conditions  here  illustrated  are  to  be  drawTi  in  the  note-books  (out  of  the 
Laboratory  if  necessary)  for  inspection. 

Expt.  91.— Reflection  hy  Plane  Mirrors. — (Apparatus:  Round  dia- 
phragm in  lamp,  plane  mirror.)  Let  a  pencil  of  parallel  rays  enter  the 
"eye"  and  fall  upon  the  plane  mirror.  Rotate  the  mirror  on  its  vertical 
and  horizontal  axes  so  that  its  surface  may  be  at  various  angles  to  the 
rays  of  light.  Observe  (.4)  that  the  angle  of  reflection  is  always  equal 
to  the  angle  of  incidence,  and  (B)  that  the  incident  ray,  the  perpendicular 
at  the  point  of  incidence  and  the  reflected  ray  are  always  in  the  same 
plane. 

Fig.  286 


Reflection  by  plane  mirrors.  Angle  a'  always  equals  angle  a,  and  always  lies  in  the  same 
plane.  So  far  as  mere  optics  are  concerned,  an  eye  at  A  sees  B  at  B',  but  there  are  subjective 
differences  which  complicate  the  experience  beyond  optical  explanation. 


Expt.  92. — Reflection  hy  Spherical  Mirrors. — (Apparatus:  Concave 
mirror.)  Have  no  diaphragm  in  the  lantern,  but  adjust  the  draw-tube 
so  that  the  rays  entering  the  eye  are  parallel. 

(A)  Concave  Mirrors. — Place  the  concave  mirror  in  the  rays  and 
observe  the  principal  focas  of  the  mirror.  This  is  a  bright  spot  2.5  cm. 
from  the  mirror,  the  latter  being  a  portion  of  the  periphery  of  a  sphere 
of  5  cm.  radius.  Turn  the  mirror  at  various  angles  and  observe 
illustrations  of  principle  A  of  the  preceding  experiment.  Place  the 
round  diaphragm  in  the  lamp  and  note  the  same  facts  under  somewhat 
different  conditions. 

(B)  Convex  Mirrors. — Remove  the  (liaj)hragm,  and  turn  the  mirror 
about  so  that  the  convex  side  is  toward  tlie  light.  Note  the  dispersion 
of  the  rays.     Draw  the  diagrams. 


OPTICS 


521 


Expt.  93. — Refraction. — (Apparatus:  Square  bottle  of  eosin  glycerin, 
round  diaphragm.)  Pass  a  pencil  of  parallel  rays  into  and  through  the 
square  bottle  of  liquid  (a  denser  medium  than  air)  lying  on  its  side  on  a 
block.  Place  the  bottle  so  that  its  side  shall  be  (.1)  at  right  angles  to 
the  rays.  Note  that  the  rays  pass  into  the  denser  medium  and  come  out 
again  into  the  air  unchanged  in  direction.  Now  (J5)  turn  the  bottle  so 
that  the  rays  shall  enter  the  botde  at  the  top  of  the  side,  the  surface  being 
very  oblique  to  the  rays.  The  latter  are  now  deflected,  broken  (refracted), 
on  entering  the  denser  medium  toward  the  perpendicular  erected  at  the 
point  of  incidence  and  on  leaving  the  denser  medium  away  from  the 
perpendicular.  The  two  bounding  surfaces  of  the  denser  medium  being 
parallel,  the  latter  deflection  is  equal  to  the  former  and  the  rays  leaving 
the  bottle  are  parallel  to  their  course  on  entering  it  Observe  the  re- 
flection also,  and  the  color  of  the  efferent  ray. 


Refraction  by  media  with  parallel  sides.  When  a  ray  (e.g.,  A)  passes  into  such  a  medium 
at  riglit  angles  to  a  side,  it  continues  straight.  When  a  ray  (e.  g.,  A')  strikes  at  an  angle,  it  is 
bent  ("broken")  toward  the  perpendicular  in  the  denser  medium  and  away  from  it  again  on 
emergence  at  E'.      Thus,  the  emergent  ray  E'  B'  is  parallel  to  A  E  C. 

Expt.  94. — Prisms. — Let  parallel  rays  in  a  narrow  pencil  pass  through 
the  prism  and  note  their  course.  Work  out  the  refraction-angles  in 
passing  through  the  prism  and  in  passing  out  of  it. 

Place  the  prism  in  the  direct  sunlight  and  observe  the  solar  spectrum 
the  rays  having  the  highest  vibration-number  being  refracted  most. 

Demonstration  of  the  Spectroscope. 

Expt.  95. — Aberration  and  the  Use  of  Diaphragms  (Iris). — (Appara- 
tus: The  three  diaphragms,  ground-glass,  and  a  white  card  for  a  screen.) 
Study  the  differences  of  the  conditions  with  convex  lenses  vAi\i  and  with- 
out a  diaphragm  to  cut  oft'  the  outermost  rays. 


522 


APPEXDIX 


(A)  Chromatic  Aberration. — Put  the  ground-glass  plate  and  the  round 
diaphragm  in  the  slide-way  of  the  lanterns.  Make  a  pencil  of  parallel 
rays  and  have  them  pass  through  the  +10  D.  lens  placed  15  cm.  away 


VIOLET. 


^  Refraction  by  media  with  oblique  sides.  A  ray  of  white  sunlight  entering  the  prism  ABC 
obliquely  is  broken  toward  the  perpendicular  and  away  from  it  on  leaving  the  denser  medium. 
The  violet  rays  are  refracted  more  than  are  the  red  rays  of  the  spectrum. 

Fig.  289 


Chromatic  aberration  comes  from  lenses  of  certain  materials  becau.se  of  the  unequal  refraction 
of  wliite  light  into  its  component  rays.  The  violet  end  of  the  spectrum  is  bent  more  than  the 
red  end,  and  the  focus  is  indefinite,  as  in  V  R.  This  is  corrected  by  using  materials  for  lenses 
which  compensate  this  unequal  refraction. 

from  the  ground-gla.ss  and  just  inside  the  eye  (this  distance  is  half-again 
as  long  as  the  lens'  focal  distance).  Place  the  card  (white  screen) 
1 5  cm.  farther  beyond  the  lens. 


OPTICS 


523 


The  image  of  the  round  illuminated  spot  on  the  ground  glass  seen  on 
the  card  has  a  violet  center  and  a  red  margin.  Double  the  distance  of 
the  card-screen  from  the  lens,  and  the  colors  change  places.     The  reason 


Fig.  290 


Refraction.  This  diagram  shows  that  a  double  convex  lens  is  optically  two  prisms  base  tc) 
base  and  that  a  double  concave  lens  is  two  prisms  apex  to  apex.  The  +  lens  refracts  toward 
the  central  ray  {,g  h),  the  —  lens  away  from  it. 

Fig.  291 


Spherical  aberration  arises  in  the  natural  fact  that  the  rays  nearer  the  lens'  center  are  refracted 
less  than  those  passing  through  its  peripheral  parts.  The  result  is  an  indeterminate  image  or 
focus,  F'  F.  Diaphragms  (as  at  D  D')  are  therefore  employed  (e.  g.,  the  iris  in  the  eye)  to  cut 
off  the  peripheral  rays,  leaving  a  relatively  clear  focus,  as  at  F. 


524 


APPENDIX 


for  this  lies  in  the  fact  that  a  double  convex  lens  is  essentially  two  prisms 
placed  base  to  base. 

{B)  Spherical  Aberration. — Place  in  the  clamp  at  the  "cornea"  a  dia- 
phragm with  an  aperture  of  1  mm.  This  cuts  off  the  spherical  aberra- 
tion bv  stopping  the  rays  which  cross  within  the  pencil  of  rays. 

Expt.  96. — Refraction  by  Convex  Lenses. — (Apparatus:  10-diopter 
double  convex  lens  in  frame,  round  diaphragm,  L-diaphragm,  black 
screen).  (A)  Let  parallel  rays  enter  the  eye.  Place  the  lens  about  5  cm. 
from  the  cornea.  Place  the  screen  10  cm.  from  the  lens  and  note  the 
focus,  and  that  on  either  side  of  that  one  position  the  image  is  indistinct. 


Fig,  292 


Convergence  of  the  ray.s  in  a  beam  of  light  is  brought  about  by  a  convex  lens,  their  point 
of  meeting  being  the  focus  F,  and  in  case  the  pencil  be  oblique  to  the  lens  F  . 

Now  replace  the  round  diaphragm  by  the  L-diaphragm  and  put  the 
screen  in  the  focus.  Note  that  the  image  of  the  L  is  inverted.  A  convex 
lens  converges  parallel  rays.  (A  lens  of  10  diopters  is  one  which  is  a 
portion  of  a  sphere  whose  radius  is  one-tenth  of  a  meter;  a  +  lens  is 
convex  and  a  —  lens  concave). 

(B)  Adjust  the  draw-tube  of  the  lamp  so  that  the  rays  diverge  into  the 
'"eye"  (have  the  tube  close  to  the  cornea).  Place  the  round  diaphragm 
in  the  clamp  outside  the  cornea;  10  cm.  from  this  diaphragm  place  the 
convex  lens,  the  openings  in  the  diaphragm  being  at  the  lens'  focus. 
The  rays  extending  beyond  the  lens  are  rendered  parallel  by  the  lens — 
the  same  process  as  in  A . 


OPTICS 


525 


Expt.  97. — Refraction  hy  Concave  Lenses. — (Apparatus:  lO-diopter 
concave  lens,  round  diaphragm,  screen.)  Let  parallel  rays  pass  into 
the  eye,  and  through  the  — 10  D.  lens.     The  rays  will  be  diverged. 

Expt.  98. — Refraction  hy  Cylindrical  Lenses. — (Apparatus:  Cylindrical 
lens  (the  thicker  one,  plane  on  one  side  and  convex  on  the  other),  round 
diaphragm,  L-diaphragm,  screen.)  Make  a  pencil  of  parallel  rays 
pass  into  the  eye  and  through  the  convex  cylinder  placed  so  that  the 


Fig.  293 


Divergence  of  the  rays  in  a  beam  of  light  is  brought  about  by  a  concave  lens.      There 
is  no  focus  save  the  mathematical  one  at  F. 


Fig.  294 


A  cylinder  in  diagram  to  show  the  principle  on  which  cylindrical  spectacle-lenses  are  made: 
a,  b,  c,  d  is  a  concavo-convex  "cylinder;"  e,  /,  g,  h,  a  plano-concave  "cylinder." 


curvature  is  from  side  to  side.  Place  the  screen  at  the  focus.  Observe 
that  the  cylindrical  pencil  of  rays  is  no  longer  round,  but  that  it  forms 
a  vertical  line  on  the  screen.  Rotate  the  lens  90°.  The  line  is  now 
horizontal.  Move  the  screen  back  and  forth  on  either  side  of  the  place 
of  clear  focus  and  observe  the  evident  shape  of  the  mass  of  rays  coming 
from  the  lens. 

Repeat  these  procedures  with  the  L-diaphragm  in  place  of  the  round 
diaphragm  in  the  lantern. 


526 


APPENDIX 


In  the  three  following  experiments  the  10  D.  lens  is  to  be  left  inside  the 
eye  close  to  the  cornea,  representing  the  lens  of  the  eye. 

Expt  99. — Myopia  and  its  Correction. — (Apparatus:  +10  D.lens,  — 2 
D.  lens,  round  diaphragm,  L-diaphragm,  black  screen.  (.4)  Myopia. — 
Let  a  pencil  of  parallel  rays  enter  the  eye.     Place  the  black  screen  at 


Fig.  295 


Diagram  of  refraction  by  cylindrical  lenses.  The  rays  in  the  vertical  plane  are  not  refracted, 
because  the  sides  of  the  lens  in  that  plane  are  parallel.  In  the  horizontal  plane  the  rays  are 
converged  by  the  cylindrical  surface  of  the  denser  medium.  The  cross  P  P'  would  therefore  be 
falsely  focussed  as  merely  a  vertical  line  O  O' .      (F.  R.  Ireson.) 

Fig.  296 


Normal  vision,  or  emmetropia,  .shows  ray.s  from  a  point  (e.  g.,  P),  focussing  exactly  on  the  retina 
in  a  point  CO).  The  dotted  line  in  front  of  the  lens  shows  the  latter's  bulging  anteriorly  in 
accommodation. 


the  focus  of  the  eye-lens — representing  normal  vision.  Move  the  screen 
back  from  the  focus-place  2.5  cm.  This  is  now  the  usual  condition  of 
a  low  degree  of  myopia  or  short-sight,  a  too  great  depth  of  the  eye-ball. 
{B)  Correction  of  Myopia. — Place  the  — 2  D.  lens  outside  the  eye  but 
close  to  the  cornea.     The  focus  is  now  carried  backward  to  the  abnor- 


OPTICS 


527 


mally  situated  screen  (retina).     For  short-sightedness  ocuHsts  prescribe 
concave  lenses. 

Expt.   100. — Hyperopia  and  its  Correction. — (iVpparatus:     +  10  D. 
lens,  +2  D.  lens,  round  and  L-diaphragms,  screen.)     (A)  Hyperopia 


Fig.  297 


Myopia  and  its  relief.  In  myopia,  owing  usually  in  large  part  to  a  too  great  antero-posterior 
depth  of  the  eye,  the  rays  focus  before  they  reach  the  retina  and  an  indefinite  image  results 
(O  0  ).  This  common  defect  is  corrected  by  concave,  minus  spectacle-lenses,  these  diverging 
the  rays  before  reaching  the  eye  so  that  the  rays  focus  farther  back  on  the  retina. 

Fig.  298 


.  Hyperopia  and  its  relief.  In  hyperopia,  owing  usually  to  a  too  great  flatness  of  the  lens  and 
cornea,  the  rays  coming  from  a  point  (P)  are  not  converged  sufficiently  to  meet  a  focus  on  the 
retina,  but  would  do  so  behind  it  were  the  latter  transparent.  This  defect  ("normal"  about 
fifty  years  of  age)  is  corrected  by  convex  spectacle  lenses,  these  converging  the  rays  so  that  they 
focus  on  the  retina. 


and  Presbyopia. — Let  a  pencil  of  parallel  rays  enter  the  eye.  Place  the 
screen  at  the  focus  of  the  eye-lens  as  before,  then  move  the  screen  for- 
ward toward  the  lens  2.5  cm.     This  represents  the  abnormal  hyperopic 


528 


APPENDIX 


eye,  except  that  more  often  the  lens  is  too  convex  rather  than  the  eye-ball 
too  shallow. 

{B)  Correction  of  Hyperopia. — Place  the  +2  D.  (thin  double  convex 
lens)  outside  the  cornea  but  close  to  it.  The  focus  is  now  brought  for- 
ward to  the  abnormally  situated  screen  (retina),  the  rays  being  more 
converged. 

Fig.  299 


The  ^^sual  defects  coming  from  astigmatism.      A  figure  like  I  tends  to  appear  either  like  //, 
or  like  ///,  because  of  the  unequal  refraction  in  the  respective  axes  of  the  eyes.      (Imbert.) 

Fig.  300 


Astigmatism  and  its  relief.  In  (regular)  astigmatism  the  refractive  media  of  the  eye  (espe- 
cially the  cornea)  are  more  convex  in  one  axis  than  in  another.  Thus,  in  the  diagram  the  rays- 
in  the  vertical  plane  are  not  converged  at  all  and  the  image  (0  O')  is  very  indistinct  in  that 
axis,  being  a  line  instead  of  a  point.  This  defect  is  corrected  by  cylindrical  spectacle-lenses  with 
the  greater  refraction  in  the  axis  in  which  it  is  lacking  in  the  eye-lens,  and  equal  to  that  defect 
in  degree.  In  the  diagram  the  spectacle-lens  c  c  refracts  only  in  the  axis  in  which  the  eye- 
lens  refracts  none. 

Expt.  101. — Astigmatism. — (Apparatus:  10  +  D.  lens,  two  +  10  D. 
cylindrical  lenses,  the  three  diaphragms,  screen.)  {A)  Astigmatism. — 
Place  the  cylindrical  lens  (curvature  lateral)  in  the  other  side  of  the  frame 
in  which  the  +  10  D.  (or  eye)  lens  is.  Let  parallel  rays  pass  into  the 
eye  through  this  "astigmatic  lens."  Place  the  screen  exactly  in  the  focus 
of  the  lens.  The  image  of  the  circular  aperture  in  the  diaphragm  is 
elongated  vertically. 

(B)  Correction  of  Astigmatism. — Now  place  before  the  cornea  of  the 
eye  the  other  cylindrical  lens  with  its  curvature  vertical.  The  image 
becomes  round.  Turn  the  correcting  lens  90  degrees,  and  the  elongation 
of  the  image  is  increased.    (See  the  diagram.) 


OSMOSIS  529 

Repeat  tliese  procedures  with  the  other  diaphragms  until  the  condi- 
tions and  principles  are  fully  understood. 

It  is  the  cornea  which  causes  usually  the  cylindricality  of  the  refracting 
media,  and  most  often  the  defect  is  congenital  although  acquired,  and 
even  changing,  astigmatism  is  by  no  means  rare,  especially  in  children. 
Oftentimes  the  curvature  is  irregular  and  bevond  the  correction  of  {ground 
lenses. 

All  sorts  of  combinations  of  astigmatism  with  myopia  or  with  hyperopia 
are  very  common. 

XI.     OSMOSIS. 

Expt.  102. —  (Apparatus:  Dialyzer  and  the  various  solutions).  (A) 
Sodium  Chloride. — Half  fill  the  inner  tube  of  the  dialyzer  with  the  solu- 
tion. Push  the  capillary  tube  downward  until  the  solution  rises  half- 
way up  in  it.  Put  the  dialyzer  in  place.  Note  the  direction  of  the 
movement  in  the  capillary  indicator.  Test  with  argentic  nitrate  for 
sodium  chloride. 

{B)  Dextrose. — Plaving  carefully  washed  out  at  the  sink  the  apparatus, 
repeat  the  experiment  with  the  dextrose-solution.  Test  the  liquid  in 
the  beaker  for  dextrose  with  Fehling's  solution. 

(C)  Glycocjen. — Repeat  the  experiment  with  the  opalescent  solution  of 
glycogen.     Test  the  contents  of  the  inner  tube. 

(D)  Potato-starch  Solution. — Repeat  the  experiment  with  the  starch- 
solution.     Test  the  liquid  in  the  beaker  with  iodine  for  starch. 

{E)  Proteid. — Repeat  the  experiment  with  egg-white  solution.  Test 
the  outer  liquid  for  protein  with  Millon's  reagent. 


LIST  OF  TOPICS  FOR  DISSERTATIONS  AND  CLASS 
DISCUSSION. 


Abiogeuesis. 

Accommodation. 

Action-currents. 

Adaptation. 

Adaptation  of  diet. 

Adipocere. 

Adrenals. 

After-images. 

Air-supply. 

Alcoliol. 

Ameba. 

Amitosis. 

Anemia. 

Anesthesia. 

Animal  experimentation. 

Anthropometry. 

Antiferments. 

Aphasia. 

Apnea. 

Aristotle. 

Arsenic  in  protoplasm. 

Arterial  circulation. 

Asphj-^xia. 

Association. 

Astigmatism. 

Ataxia. 

"Athletic  lieart." 

Atmospheric  pressure. 

Auscultation  and  percussion. 

Bacteria  in  health. 

liathing. 

Bernard,  Claude. 

Bile. 

Blood-composition. 

Biood-7)ressure. 

Bodily  Ixiauty. 

Bodily  growth. 

Brunner's  glands. 

Calcium  and  magnesium. 

Calorimetr>-. 

Capillary  circulation. 

Cardiac  massatre. 

Cardiac  tonus. 

Cell-div'ision. 

Oillular  differentiation. 

Cerebellum. 

Cerebral  localization. 

Cerebral  ventricles. 

Cerebrospinal  fluid,  etc. 

Chemotaxis. 

r.'holesterin. 


Classification  of  proteids. 

Clothing. 

Coagulation. 

College  athletics. 

Color-vision. 

Composition  of  the  blood. 

Composition  of  the  feces. 

Composition  of  the  sweat. 

Composition  of  the  urine. 

Consciousness. 

Conservation  of  energy. 

Constipation  and  diarrhea. 

Cooking. 

Coordination  of  the  heart's  movements. 

Cortex  cerebri. 

Cross-suturing  of  nerves. 

Cyclic  \'omiting. 

Ciliated  epitlielium. 

Daphnia. 

Death. 

Definition  of  healtli. 

Definition  of  life. 

Deglutition. 

Dental  hygiene  in  the  schools. 

Depressor  nerve. 

De\elopment  of  vital  capacity. 

Development  of  voluntary  action. 

Diaphoresis. 

Diets. 

Dignity  of  medicine  and  dentistry. 

Diuresis. 

Dyspepsia. 

Eddyism. 

Edema. 

Electrotonus. 

Elimination  of  poisons. 

Embryology  of  the  circulatory  organs. 

Em])ryology  of  the  digestive  organs. 

Embryology  of  tlie  nervous  system. 

Embryology  of  the  respiratory  organs. 

Embryology  of  the  urf)genital  organs. 

Emotional  expression. 

Endurance. 

Epiglottis. 

Erythrocytes. 

Estimation  of  nitrogen. 

Eustachian  tubes. 

Evolution. 

Eye-movements. 

Eye-strain. 

Fasting.  , 


LIST  OF  TOPICS  FOR  DISSERTATIONS  AND  DISCUSSION     531 


Fatigue  and  exhaustion. 

Fertilization. 

Fetal  circulation. 

Fever. 

First  heart-souml. 

Food-adulteration. 

Galen. 

Galvanism. 

Gelatin  as  a  food. 

Geotaxis. 

Giantism  and  dwarfism. 

Glycogen. 

"  Going  stale." 

Graphic  method. 

Habit. 

Hair. 

Hallucinations  and  illusions. 

Happiness  and  bodily  function. 

Harvey,  William. 

Health-value  of  good  teeth. 

Helen  Kellar. 

Heimholtz,  Herman  L.  F. 

Hematology. 

Hemoglobin. 

Hemoglobin  and  chlorophyll. 

Hemophilia. 

Heredity. 

Hibernation. 

Holmes,  Oliver  Wendell. 

Homeopathy. 

Human  embryos. 

Hunger. 

Hunger  and  thirst. 

Hunter,  John. 

Hypnosis  and  suggestion. 

Icterus. 

Ileocecal  valve. 

Immunity. 

Individuality. 

Inductorium. 

Infantile  dige.stion. 

Inflammation. 

Ingenuity  and  originalitv. 

Inhibition. 

Inhibition  of  reflexes. 

Inspired  and  expired  airs. 

Instinct. 

Internal  capsule. 

Internal  nutrition. 

Internal  respiration. 

Invigoration. 

Invironment. 

Ions. 

Iron. 

Irritability. 

Kinesthesia. 

Kreatinin. 

Lactic  acid. 

Lecithin. 

Legerdemain. 

Leukocytes. 

Life-periods. 

Light. 

Liver. 

Local  signs. 


Lymph. 

Lj'niph  and  bodily  exercise. 

Jjymph-glantls. 

Manometers. 

Massage. 

Mastication. 

"Maternal  impressions." 

Mechanics  of  the  joints. 

Medical  school-supervision. 

Medulla  oblongata. 

Meissner's  and  Anerbach's  plexu.ses. 

Metabolism. 

Metric  measures. 

Micturition. 

Milk. 

Mitosis. 

Movements  of  the  alimentary  cana!. 

Mucus. 

Miiller,  Johannes. 

Muscle-fabric. 

Muscle-fatigue. 

Muscular  "automaticity." 

Muscular  contraction. 

Muscular  coordination. 

Muscular  metabolism. 
Muscular  tonicity. 

Mjrograms. 

Myoids. 

Movements  of  the  alimentarj'  canal 

Nasal  respiratory  tract. 

Natural  organic  defences. 

Necrobiosis. 

Negative  variation. 

Nervous  impulse. 

Neurofibril  theory. 

Neuromuscular  mechanism. 

Neurone  theory. 

Nissl's  bodies. 

Nucleic  acid. 

Nutrition  of  heart. 

Obesity. 

Old-age. 

Optic  thalami. 

Ordeals. 

Organic  electricity. 

Organic  heat. 

Organic  light. 

Organic  production  of  water. 

Organic  soaps. 

Organ  of  Corti. 

Origin  of  blood-corpuscles. 

Origin  of  life  on  earth. 

Origin  of  lymph. 

Osmosis. 

Osteopathy. 

Overeating. 

Ovulation  and  menstruation 

Oxidases. 

Oxidation. 

Pain. 

Parturition. 

Pehdc  congestion. 

Perception  of  causality. 

Perception  of  space. 

Perception  of  time. 


.32 


APPEXDIX 


Peritoneum. 

Pfliiger's  contraction-law. 

Phagocytosis. 

Phosphorus  and  sulphur. 

Physical  exercise. 

Physicians  as  teachers  of  right-living. 

Physics  in  physiology. 

Physiological  fistulte. 

Physiological  superstitions. 

Physiology  in  physical  education. 

Pigment. 

Poisoning  from  coal-gas. 

Pons  varolii. 

Pregnancy. 

Production  of  urea. 

Proteids  of  the  blood. 

Protoplasm. 

Protoplasm  and  proteid. 

Protoplasmic  unit. 

Psychology  in  the  medical  schools. 

Pyloric  \'alve. 

Pituitary  body. 

Psychophysical  cppability. 

Pyrexia. 

Quantity  of  blood. 

Kapidity  of  nerve-force. 

Reaction-time. 

Reflex  action. 

Regeneration. 

Regeneration  of  nerve. 

Relations  of  physiology. 

Relative  heat-values  of  foods. 

Relative  value5.  of  tissues'  metabolism. 

liemoval  of  cortex  cerebri. 

Renal  hydraulics. 

Rennin. 

Respiration  of  the  fetus, 

Respiratorv  quotient. 

Rest. 

Retina. 

Reverse  ciliary  movement. 

Rheumatism. 

Rods  and  cones. 

Rumination. 

Running  as  an  exerci.se. 

Relations  of  mind  to  body. 

Renal,  hepatic,  and  intestinal  colic. 

Rfintgen-ray  aspermia. 

Saliva. 

School-room    ventilation    by   opened 

windows. 
Sea-sickne.ss. 

Secondary  sexual  characteristics. 
Secretion. 

Secretion  of  foreign  substances  in  milk. 
Secretion  of  milk. 
Self-digestion  of  .stomach. 
Semen. 

Semicircular  canals. 
Sen.sation  and  afferent  impulses. 
Sensitivity  of  the  viscera. 
Sen.sory  cerf;t)ral  tract.s. 
.Scrum-therapy. 
Sexual  education. 
Slioek,  (surgical). 
Shoes. 


Similarity  of  animals  and  plants. 

Simple  sense-organs. 

Skill  and  cleverness. 

Skin-al3sor)it  ion. 

Skin-varnishing. 

Sleep. 

Sodium  and  potassium. 

Source  of  muscular  energy. 

Sources  of  animal  heat. 

Specific  energy  of  the  ner\es. 

Spectra  of  the  liemogloliins. 

Speech  and  language. 

Spinal  paths. 

Spinal  reflexes. 

Splanchnic  nerves. 

Spleen. 

Starvation. 

Statistical  method. 

Stereognosis. 

Stimulants  Acrsus  depressants. 

Stuttering,  etc. 

Subconsciousness  and  nervous  impulses. 

vSuccus  entericus. 

Sugar  as  a  food. 

Superficial  burns. 

Sweat-secretion. 

"Systems"  of  physical  education. 

"Taking  cold." 

Taste  and  smell. 

Tea  and  coffee. 

Teeth. 

Tetanus. 

Theory  of  enzymes. 

Thermotaxis. 

Thirst . 

Throml:)ocytes. 

Thymus. 

Thyroid. 

Tobacco. 

Tongue. 

Transfusion,  etc. 

Trophism. 

Ultra-microscopy. 

^'agus  in  respiration. 

Vagus  nerve. 

A'^ariation  by  mutation. 

\'ariation  by  natural  selection. 

Vasomotion. 

Vasomotion  in  the  brain. 

^^asomotor  centers. 

Vegetarianism. 

"\'el()city  of  blood-stream. 

^'elocity  of  pulse-wa\e. 

^'enous  circulation. 

X'entilatiori. 

\'eiitriloquism. 

A'ermiform  appendix. 

Ve.salius. 

Mcarioiis  functif)n.  ^ 

^'o(■al  cords.    | 

A'f)luntary  nci'uni. 

\'(iluiitarv  control  f)f  the  heart. 

\'oluntary  muscular  contraction. 

Vomiting. 

Walking. 

What  a  "nerve-center"  is. 


r'OXVERSION  TABLES. 


CoRKE.spo.vt)iN'(;  Degrees  in  the  Fahke.vheit  anu  Centigrade  Scales. 


CeyU. 


Fahr. 


Cent. 


Fa/tr. 


Fahr. 


Cent. 


Fahr. 


To  turn  C.°  into  F.°,  multiply  by  9,  divide  by  5,  and  add  32. 
To  turn  F.°  into  C.°,  deduct  32,  multiply  by  o,  and  divide  by  9. 

Measures  of  Length. 


Cent . 


100° 

212.0° 

38° 

100.4° 

500° 

286.0° 

90° 

32.2° 

98° 

208.4° 

36° 

96.8° 

450° 

232.2° 

85° 

29.4° 

96° 

204.8° 

34° 

93 . 2° 

400° 

204.4° 

80° 

26.7° 

94° 

201.2° 

32° 

89.6° 

350° 

176,7° 

75° 

23 . 9° 

92° 

197.6° 

30° 

86.0° 

300° 

148.9° 

70° 

21.1° 

90° 

194.0° 

28° 

82 . 4° 

212° 

100,0° 

65° 

18.3° 

88° 

190.4° 

26° 

78.8° 

210° 

98,9° 

60° 

15.5° 

86° 

186.8° 

24° 

75.2° 

205° 

96.1° 

55° 

12.8° 

84° 

183.2° 

22° 

71.6° 

200° 

93.3° 

50° 

10.0° 

82° 

179.6° 

20° 

68.0° 

195° 

90.5° 

45° 

7.2° 

80° 

176.0° 

18° 

64.4° 

190° 

87.8° 

40° 

4.4° 

78° 

172.4° 

16° 

60.8° 

185° 

85.0° 

35° 

1.7° 

76° 

168.8° 

14° 

57.2° 

180° 

82.2° 

32° 

0.0° 

74° 

165.2° 

12° 

53 . 6° 

175° 

79.4° 

30° 

—  1.1° 

72° 

161.6° 

10° 

50.0° 

170° 

76.7° 

25° 

—  3.9° 

70° 

158 . 0° 

8° 

46.4° 

165° 

73.9° 

20° 

—  6,7° 

68° 

154.4° 

6° 

42.8° 

160° 

71.1° 

15° 

—  9.4° 

66° 

150.8° 

4° 

39.2° 

155° 

68.3° 

10° 

—12.2° 

64° 

147.2° 

2° 

35,6° 

150° 

65.5° 

5° 

—15,0° 

62° 

143.6° 

0° 

32.0° 

145° 

62.8° 

0° 

—17,8° 

60° 

140.0° 

—  2° 

28,4° 

140° 

60.0° 

—  5° 

—20 , 5° 

58° 

136.4° 

—  4° 

24.8° 

135° 

57.2° 

—10° 

—23.3° 

56° 

132.8° 

—  6° 

21.2° 

130° 

54.4° 

—15° 

—21.6° 

54° 

129.2° 

—  8° 

17.6°     ; 

125° 

51.7° 

—20° 

—28 . 9° 

52° 

125.6° 

—10° 

14.0° 

120° 

48.9° 

—25° 

—31.7° 

50° 

122.0° 

—12° 

10.4° 

115° 

46.1° 

—30° 

—34.4° 

48° 

118.4° 

—14° 

6.8° 

110° 

43.3° 

—35° 

—37.2° 

46° 

114.8° 

—16° 

3.2° 

105° 

40.5° 

—40° 

—10.0° 

44° 

111.2° 

—18° 

—0.4° 

100° 

37.8° 

—45°  ■ 

—42.8° 

42° 

107.6° 

—20° 

—4.0° 

95° 

35,0° 

—50° 

— 15 . 6° 

40° 

104.0° 

1  Myriameter, 

Mm. 

= 

10000,0 

1  Kilometer, 

Km. 

= 

1000,0 

1  Hectometer, 

Hm. 

= 

100,0 

1  Decameter, 

Dm. 

= 

10,0 

1  Meter, 

M. 

= 

1,0 

1  Decimeter, 

dm. 

= 

.1 

1  Centimeter, 

cm. 

= 

.0: 

1  Millimeter, 

mm. 

= 

.0( 

M. 


6,2137 

+ 

miles. 

4.9710 

+ 

furlongs. 

19.8840 

+ 

rods. 

32.8086 

feet. 

39.3704 

inches. 

3,93704 

" 

0.393704 

" 

0,0393704 

•'' 

Measures  of  Capacity. 


1  Myrialiter, 

Ml. 

= 

10000,0 

L.     = 

2641.7890        +  gallons. 

1  Kiloliter, 

KI. 

= 

1000,0 

"       = 

264.1789        + 

1  Hectoliter, 

HI. 

= 

100,0 

'•■       = 

26.4178        + 

1  Dekaliter, 

Dl. 

= 

10.0 

'•      = 

2.6417        + 

1  Liter, 

L. 

= 

1,0 

"      = 

33.8149        +  fluidounces 

1  Deciliter, 

dl. 

= 

.1 

"       = 

3.38149      + 

1  Centiliter, 

cl. 

= 

.01 

'•       = 

.338149    +   fluidounce. 

1  Milliliter, 

ml. 

= 

.001 

"      = 

.0338149  + 

1  Cubic  centimeter, 

c.cm. 

= 

.001 

= 

.0338149  + 

534 


APPENDIX 


Measures  of  Weight. 


1  Myriagram, 

Mg. 

= 

10000.0 

Gm. 

= 

22.0461        + 

pounds 

1  Kilogram, 

Kg. 

= 

1000.0 

" 

= 

2.2046        + 

1  Hectogram, 

Hg. 

= 

100.0 

•' 

= 

3.5273        + 

av.  oz. 

1  Dekagram, 

Dg. 

= 

10.0 

" 

= 

154.3235639 

grains. 

1  Gram, 

Gm. 

= 

1.0 

" 

= 

15.43235639 

" 

1  Decigram, 

dg. 

= 

.1 

" 

= 

1.543235639 

" 

1  Centigram, 

eg- 

= 

.01 

" 

= 

. 1543235639 

" 

1  Milligram, 

mg. 

= 

.001 

" 

= 

.01543235639 

** 

Comparative  Table  of  Metric  with  Avoirdupois  and  Apothecaries'  Weights. 


Names. 


Milligram 

Centigram 

Decigram 

Gram    . 

Dekagram 

Hectogram 

Kilogram 

Myriagram 


Numerical 
expressions. 

Gram.s. 

0.001 

0.01 

0.1 

1.0 

10.0 

100.0 

1000.0 

10000.0 


Equivalents  in 
grains. 


Equivalents  in 

avoirdupois 

weight. 


Equivalents  in 

apothecaries' 

weight. 


Grains. 


.01543 

. 15432 

1 . 54323 

15.43235  . 

154.32356 

1543.23563 

15432.35639 

154323.56390 


2 
22 


...     1.5  I 
.  ..  15.4 

i 45.00 
3^12.00 
3^10.47 
i    14.8  I 


3 

32 

321 


1.5 
15.4 
34.0 
43.0 
12.4 

3.5 


Comparative  Table  of  Metric  and  Apothecaries'  Fluid  Measure. 


Cubic  centimeter. 

Minims.                            f 
1.0 

5 

f3 

in 

0.06161 

0.30805 

5.0 

0.61610 

10.0 

1.0 

16.23 

5.0 

81.15 

1 

21  J5 

10.0 

162.30 

2 

42.3 

20.0 

324.60 

5 

24.6 

30.0 

486.90 

r 

0 

6.9 

40.0 

649.20 

1 

2 

49.2 

50.0 

811.50 

1 

5 

31.5 

60.0 

973 . SO 

2 

0 

13.8 

70.0 

1136.10 

2 

2 

56.1 

80  0 

1298.40 

2                        5 

38.4 

90.0 

1460.70 

3                        0 

20.7 

100.0 

1 623 . 00 

3                        3 

3.0 

250.0 

4057 . 50 

8                        3 

37.5 

500.0 

8115.00                     1 

6                        7 

15.0 

1000.0 

162:W.OO                     3 

3 

6 

30.0 

1  Gram  =   15.432  grains.  1  Grain  =  0.065  gram. 

1  Drachm  (troy)  =  3.888  grams  (approximated  4). 

1  Troy  ounce  =  31.103  grams  (approximated  30  or  32)  or  480  grains. 

1  Avoirdupois  ounce  =  28.35  grams  (approximated  28.5)  or  437.5  grains. 

1  Kilogram  =  1000  grams  =  2.2  a\'oirdupois  pounds. 

1  Minim  =  0.062  c.c. 

1  Fluidraclirn  =  3.7  c.c.  (approximated  4). 


TABLES  OF  MEASUREMENT  5:35 

1  Wine  Huidouncc  =  29.57  c.c.  (upproxiiuatcd  'AO)  or  the  volume  of  455. (>  grains  of 
water  at  02°  F. 

1  Imperial  fluidounce  =  28.39  c.c.  (approximated  28.5)  or  the  volume  of  4.37.5 
grains  of  water  at  62°  F. 

1  Liter  =  1000  c.c.  =  2.11  wine  pints  or  1.76  Imperial  pints,  or  33.815  fluidounces. 

3  Gallons  of  water  =  25  avoirdupois  pounds  at  60°  F.     (1  Gallon  =  8.331  lbs.) 

1  Mm.  (millimeter)  =  _,'5  of  an  inch. 

1  Cm.  (centimeter)  ==  j  of  an  inch. 

1  Inch  =  25  millimeters  or  2^  centimeters. 

1  (y.c.  (cubic  centimeter)  =  16.23  minims  or  0.27  fluidraclim  or  0.0338  fluidounce. 

1  Fluidounce  =  29.57  cubic  centimeters  at  4°  C. 

1  Grain  =  0.06479  gram  or  64.79  milligrams. 

1  Mg.  (milligram)  =  0.01.543  grain  (practically  ^h  grain). 

1  Pound  avoirdupois  =  453.6  grams. 

Rule. — To  convert  troy  ounces  to  avoirdiipois  add  10  per  cent. 

(The  difference  between  a  troy  ounce,  480  grains,  and  an  avoirdupois  ounce, '437. 5 
grains,  is  42.5  grains,  or  about  iO  per  cent,  of  the  latter.  To  be  exact,  substract  1.5 
grains  for  each  troy  ounce.) 

Rule. — To  convert  avoirdupois  ounces  to  troy,  subtract  one-eleventh. 

(   62.425  pounds  at  4°  C.  (39.1°  F.) — maximum  density. 

One  cubic  foot  of  water  '   ^^.418  pounds  at  0^  C.  (32°  F.)-freezing  point. 

une  cubic  loot  ot  t\  ater  ,   ,,2.35.5  pounds  at  16=  C.  (62°  F.)— standard  temperature. 
'^^  ^^^'^^  I   .59.640  pounds  at  100°  C.  (212°  F.)— boiling  point. 

I   57.5  pounds  in  form  of  ice. 

1  Cubic  foot  water  =  7.485  wine  gallons. 

1  Avoirdupois  pound  water  =  27.7  cubic  inches. 

1  Cubic  inch  water  =  0.03612  avoirdupois  pounds. 

A  pressure  of  1  pound  per  square  inch  requires  a  depth  of  2.31  feet  of  water. 

The  latent  heat  of  water  =  79  thermal  units  Centigrade  (or  142.2  units  Fahrenheit). 

The  latent  heat  of  steam  =  536  thermal  vmits  Centigrade  (or  964.8  units  Fahren- 
heit). 

SURFACE-ME.\.SUREMENT. 

1  Square  meter  =  about  1550  square  inches  (or  10,000  square  centimeters  or 
10.75  square  feet. 

1  Square  inch  =  about  6.4  square  centimeters. 
1  Square  foot  =  about  930  square  centimeters. 

Energy-measure. 

1  Kilogrammeter  =  about  7.24  foot  pounds. 
1  Foot  pound  =  about  0.1381  kilogrammeters. 
1  Foot  ton  =  about  310.0  kilogrammeters. 

Heat-equivalext. 
1  Kilocalorie  =  424  kilogrammeters. 

One  Decimeter. 
IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIUIIII 


5 

Centimeters. 


IM>EX. 


AnnoMixAL  nerves,  9-t 
Aberration,  521 
Absorption,  216 

bv  respiratory  surface,  100 

bV  skin,  323  ' 

by  villi,  218 

diagram  of,  217 

of  fats,  21S 
Accommodation  of  the  eye,  341 
Acetonuria  in  pregnancy,  444 
Acid  albumin,  191 
Acromegaly,  50,  228 
Action  as  will,  410 

current,  491,  505 

precedes  the  contraction,  505 
Adaptation,  47 
Adjustments  of  the  eves,  339 
Adolescence,  429,  449 
Adrenalin,  228,  261,  507 
Adult  age,  453 

Affecti\e  tone  of  the  emotions,  409 
Afferent  endings,  329,  etc. 

organs,  327 

paths,  328 
After-images,  360 
Ages.  448 
Agraphia,  397 
Air,  composition  of,  131 

excretion  in,  251 
Albuminoids,  30,  135,  139 
Albumins,  .30 
Alcohol,  163 

heat-value  of,  165 
Alimentary  canal,  172 
Alimentation,  1.33 
Aheoli  of  the  lungs,  105,  107 
Ameba,  18,  47,  461 
.\meboid  movements,  38,  461 
Amido  acids,  204 
Amitosis,  44 
Annnoniiun  carbamate,  241 

carbonate,  241 

lactate,  241 
Amphiaster,  46 
Ampulla',  369 
Amvlopsin,  206,  188 
Amylose,  30,  190 
Anabolism     (assimilation),      36,    219, 

220 
Anaphase,  46 


Anelectrotonus,  512 
Anesthesia,  426,  479 

experiences  imder,  427 
Animal  heat,  228 
Anolis  stethogram,  478 

stethograph,  120 
Anterior  pj-ramids,  76 

roots,  90 
Antiperi-stalsis,  210,  467 
Antrum,  181,  184 
Aorta,  290 
Aortic  incompetency,  474 

stenosis,  474 
Aphasia,  396 
Apnea  in  Anolis,  479 
Apparatus,  469 
Appetite,  144,  235 
Arachnoid,  62 
Arterial  pressure,  284 
Arteries,  functions  of,  298 

rapidity  of  blood-current  in.  282 

recoil  of,  279 

structure  of,  298 
Aspects  of  consciousness,  403 
Aspennia,  439 
Asphyxia,  476 

by  water-gas,  257 
Aspiration    of    the    thorax,     114,    280, 

308 
Assimilation  (anabolism),  36,  220 
Associated  movements,  390 
Association,  65 

of  percepts  and  concepts,  416 
Association-areas,  73 
Association-tracts  in  the  cord,  81,  82 
Astigmatism,  .525,  528 
Ataxia,  335 

Atropine  antidote  to  muscarin,  .507 
Attention,  407 

increased,  in  feeling,  409 
Attitude,  bodil>-,  390 
Attraction-sphere,  46 
Audition,  345 
Auditory  centers,  72 

nerves,  88 
Auerliach's  plexus,  203 
Augmentation  of  heart,  515 
Auriculo-\  entricular  incompetency,  474 

stenosis,  474 
Autochthonic  centers,  78 
Automatic  centers,  78 
"  Automaticity"  of  muscle,  ,501 


«i. 


538 


INDEX 


Autonomic  nerves,  9G 
Axis  cylinder,  56 
Axolennna,  57 

B 

Bacteria  in  gut,  212 

saprophytic.  460 
"Baskets"  of  nerve-fibrils,  58 
Beat  of  the  heart,  289 
Bile,  action  of,  in  digestion,  204,  207,  209 

composition  of,  209 

secretion  of,  209 
Biliarv  salts,  208 
Bilirubin,  209 
Binocular  \ision,  339,  345 
Biogen.     See  Protoplasm,  17 
Bioplasm,  17 
Bladder,  urinary,  248 
Blanching  of  hair,  325 
'•Bleeders,"  260 
Blood,  254 

chemical  composition  of,  254 

coagulation  of,  260 

color  of,  258 

composition  of,  254 

gases  of,  113 

general  characters  of,  258 

in  pregnancy,  444 

list  of  regular  constituents  of,  255 

of  Daphnia,  466 

phj-sical  characters  of,  258 

quantity  of,  258 
Blood-atoms,  270 
Blood-corpuscles,  262 

chemistry  of,  256 

relations  of  spleen  to,  266,  268 

structure  of,  262 
Blood-plasma,  255 
Blood-platelets,  269 
Blood-pressure,  281,  283,  284 
Blood-serum,  262 
Blood-temperatures,  231 
Bodily  aspects  of  feeling,  410,  419 

exercise,  results  of,  on  muscle,  389 
Brachionus,  463 
Brain,  63 

blood-supply  of,  62 

de\elopmeiit  of,  53 
]irain-localization,  69 
Bread,  143,  146 
lireath-rate,  122 

of  Anolis.  477 

of  various  brutes,  124 
Bronchi,  103,  105 
Bronchial  breatliing,  126 
Brunner,  glands  of,  181,  197 
Bulb  (medulla),  76 

nerve-centers  in.  76-78 
Butter,  143 


Caffkine,  160 
Calcium,  261 


Calculation  of  food-values,  143 
Calluses,  315 
Calories,  142 
Calorimeter,  141 
Calorimetry,  141 
Canal,  medullary,  SO 
Canals,  semicircular,  3(59 
Cane-sugar,  146,  161 
Capillary  circulation,  304 

demonstration  of,  476 

electrometer,  471 

nerve-plexus,  108 

structure,  305 
Capillaries,  blood-pressure  in,  284 

functions  of,  304,  305 
Capsule,  internal,  64 
Carbohydrates,  30,  32 

absorption  of,  218 

digestion  of,  171,  189 

metabolism  of,  220 
Carbon  dioxide,  113 

daily  quantity  of,  103,  251 

food  cycle,  134 

in  the  blood,  113 
in  the  tissues,  101,  119 
Cardiac.     See  Heart,  278,  etc. 
Cardiograms,  286 
Casein,  154 
Catelectrotonus,  512 
Cell,  diagram  of,  22 

tj-pical  animal,  47 
Cell-death,  456 
Cell-division,  44 

direct,  44 

indirect,  45 
Cells,  21 

animal  and  vegetal,  460 

numbers  of,  in  human  adult,  100 

reproductive  process  of,  44 
Cellulose,  150,  206 
Center,  neural,  69 
Centimeter  rule,  535 
Central  nervous  system  of  the  dove,  54 
Centrosomes,  46 
Cereals,  148 
Cerebellum,  78 

connections  of,   with   cerebrum,  69, 
78 

cortex  of,  77 

histology  of,  77 

Burkinjc  cells  of,  (il,  77 
Cerebral  convolutions,  66,  69 

localization,  69 

^■asomotion,  62 
Cerebrin,  62 

Cerebro-spinal  fluid,  62,  276 
Cerebrum,  63 

connections  of,  with  spinal  cord,  69 

extirpation  of,  517 

fibers  of,  67 

general  psychomotor  \i8e8  of,  390 

histology  of,  68 
Cerumen,  322 

rhang(!f\ilness  of  consciousness,  401 
Changes  in  strength  of  stimulus,  487 


INDEX 


539 


Clieiui-surlace-tensiDii  tlieory  of   muscle- 
action,  380 
Cheinotaxis.  43,  441,  519 
Chiasma,  optic,  339 
Childhood,  449 
Chlorophyll,  256 
Chocolate,  162 
Choice,  411 
Cholesterin,  253 
Chorda-  tendinse,  291 
Chromatic  aberration,  522 
Chromatin,  23 
Chromoproteiils,  30 
Chromosomes,  46 

number  of,  in  different  animals,  46 
Chronograph,  471 
Chyle,  255 
Ciliary  movement,  39,  468 

muscle,  341 
Circulation,  277 
causes  of,  278 
in  childhood,  451 
in  the  arteries,  298 
in  the  capillaries,  304 
in  the  cranial  cavity,  62 
in  the  heart-walls,  292 
in  the  veins,  310 
of  bile  salts,  253 
rapiditv  of,  282 
time,  283 
Cleverness,  390 
Climacteric,  435 
Clot,  blood,  261 
Coagulation,  blood,  260 
milk,  156,  193,  270 
Cochlea,  347 

distribution  of  nerves  in,  348 
uses  of  different  parts  of,  348 
Cocoa,  162 
Coffee,  161 
Cognition,  414,  420 
Coitus,  369,  437 
Cold,  231 

and  heat,  relation  of,  to  contraction, 

495 
sense,  364 
spots,  365 
Collaterals,  61 

Collection  by  the  cord,  82,  89 
Colon,  209 
Coloration,  324 
Color-blindness,  345 
perception,  344 
Colostrum,  156,  447 
Columns  of  the  cord,  80 
Combustion-equivalents,  143 
Compensatory  pause  of  heart,  504 
Complemental  air,  128 
Compounds  constant  in  protoplasm,  26 
Compression  of  arteries,  281 

of  Ij-mphatics,  308 
Conation,  410,  420 
Concave  lenses,  525 
Conception,  mental,  416 
sexual,  439 


Concepts,  41(5 

varieties  of,  417 
Condiments,  135 

Conduction  in  the  spinal  cord,  80 
Conductivity,  42 
Cone-cells,  337 
Cones,  337 

Conference-topics,  530 
Connective  tissue,  pigmented,  324 
Consciousness,  43,  399 

aspects  of,  403 

characteristics  of,  401 
Constituents  of  animal  body,  30 
Contact,  sense  of,  351 
Continuitv     of     consciousness,      402, 

423 
Contractile  system,  374 
Contraction,  law  of,  498 
Contraction-wave    of     muscle,      497, 

499 
Convex  lenses,  524 
Convolutions,  cerebral,  6(5 
Contrast-effects,  360 
Cookery,  149 
Coordination,  53,  86 

of  cilian.^  motion,  469 
Copulation,  437 

Cord,  spinal,  79.     See  Spinal  conl. 
Cords,  vocal,  395 
Cornea,  338 
Corpora  quadrigemina,  74 

striata,  74 
Corpus  albicans,  434 

"internal  secretion"  of,  433 

luteum,  433 
vera,  434 
Correction  of  astigmatism,  528 
hyperopia,  528 
myopia,  526 
Corresponding    points    in    the    retina, 

339 
Cortex  cerebri,  68 
cells  in,  68 
psychomotor  (?),  70 
Corti,  organ  of,  348 
Coughing,  125 
Cowper,  glands  of,  439 
Cranial  nerves,  88 

sj'stem  of  the  autonomics,  97 
Cream,  156 

Creatin  and  creatinin,  241,  383 
Creation,  17 
Cretinism,  227 
Crura  cerebri,  64 
Crystalline  lens,  338 
Current  of  rest  and  current  of  action,  491, 

492 
Cuticle,  312  "    ! 

Cvanic-evolutionar\-  theory-  of  life's  ori- 
gin, 18 
Cyanogen,  19  . 
"Cycle"  of  iieart-events,  288 
Cyclops,  465 
Cylindrical  lenses,  525 
C-\iioplasm,  23,  30 


540 


INDEX 


E 


Dandrvff,  323 
Daphnia.  465 
Death,  4.56 
Decidua  reflexa,  442 

vera.  442 
Defecation,  211 
Deglutition,  179 

duration  of,  180 

protection    of    air-]-)assages    during, 
ISO 
Delusions,  426 

danger  of  persons  with,  426 
Dendrites,  61 
Dentitions.  174 
Depressor  nerves,  297 
DeiTual  functions,  diagram  of,  312 
Desiccation,  4.57 
Deuteroalbumose,  192 
Development.  44S 
Dextrin.  1.S9 
Dextrose.  30,  .32,  190,  218 

osmosis  of,  .529 
Diabetes,  243 

Diagram  suggesting  the  complexity  and 
instabilitv  of  a  protoplasmic   particle, 
27 
Diapedesis,  269,  305 
Diaphragm,  lOS 
Diaphragms,  .521 
Diastase,  animal,  30,  189 
Diastolic  action,  190 
Diaster,  46 

Dicrotic  pulse,  472,  474 
Diet,  137 

for  nursing  mothers,  448 

.six  requirements'in,  137 
Diffusion  in  tlie  hmgs.  117 
Digestion,  36,  170 

clianges  in.  in  pregnancy,  443 

colonic.  212 

duration  of,  in  stomach,  185 

gastric,  18S 

in  Amelja,  50 

in  .small  intestine,  199 

influence   of  various   conditions   on, 
179 
7>ige.stive  zymolysis,  diagram  (jf,  206 
Dionea.  .53,  172 
Diopter.  .524 
Direction  of  sounds,  351 

of  stinnilating  current.   19:5 
Di.scrimination  of  pitch,  350 
I  disease,  diet  in,  1.59 
Dis.sertations,  list  of  topics  for,  530 
Distribution  bv  the  cord,  82 
Dream.s,  424 
Drop.sy,  310 

Drug-actions  .shown  in  Daphnia,   168 
Dry-cell,  470 
Ductless  glands,  225 
Duodenum,  197,  226 
Dura  mater,  62 
Duration  of  stimulus,  484 


Ear,  external,  347 

internal,  348 

middle,  347 

ossicles  of,  347 
Edema,  310 
Eggs,  142 

Eighth  nerve,  347,  369 
Elastic-tissue  spindles,  353 
Electrodes,  non-polarizable,  471 
Electrolytic  salines  on  heart,  503 
Electrotaxi.s,  518 
Electrotonus,  512 

Elements  constant  in  protoplasm,  26 
Eleventh  nerve,  88,  295 
Embr\'ology  of  Daphnia,  468 
Emetics,  186 
Emmetropia,  526 
Emotion,  397,  408 
Emotional  reactions,  397 

centers  of,  74 
Encephalon,  63,  517 

connections  of,  with  spinal  cord,  60 
End-bulbs,  330,  354 
Endosmosis  and  exosmosis,  221 
Energy,  42 

varieties    of,   which    will    stimvdate 
muscle,  481 
Energ}--values  of  foods,  140 
Engelmann's  incisions,  .501 
Enteric  system  of  the  autonomics,  97 
Enterokinase,  30,  204,  207 
Enzymes,  30,  178,  188 
Eosinophiles,  267 
Epidermis,  313 
Epiglottis  in  deglutition,  105 
Epileptiform  con\ulsions,  71 
Epithelia,  41,  221 
Epithelio-muscular  cells,  373 
Epitome  of  animal  functions,  466 
Equilibrium,  75,  369,  390,  518 
Erepsin,  30,  204 
Erythrocytes,  263 

chemical  composition  of,  256 

number  of,  265 

physieal  nature  of,  264 

places  of  origin  of,  26() 
E.sopnageal  ner\'es,  179 
l">so|jhagus,  179 
Kuglena,  36,  4()3 
Eustachian  tube,  348 
Evacuation  of  bladder,  249 

of  rectum,  211 
Evolution  of  neiu-one,  519 
Excitement  in  feeling,  409 
Exciting  vs.  efficient  energv,  98 
Excretion,  37,  239 
Exhaustion,  370 
Experience,  .399 

Experiences  under  anesthesia,  427 
Expiration,  muscles  of,  109 
"Expression"  of  the  emotions,  397 
Extra  contraction  of  heart,  504 
Extrinsic  eye-mu.sdes,  .339 


IXDJ'JX 


.")41 


Eye,  336 

movements,  340 
ol"  Daphnia,  4 OS 
refraction  in,  33S,  526 
section  of  front  of,  342 
simple  schematic,  338 

Eyeball,  muscles  of,  340 


Fabuip,  neural,  rt'S 
Facial  ner\e,  8S 
Fallopian  tubes,  432 
Fatigue,  370 

of  muscle,  490 

of  nerve-cells,  oS 
Fats,  30,  31 

absorption  of,  217,  218 

digestion  of,  206 

metabolism  of,  220 
Fauces,  180 
Feces,  252 
P^ecunilation,  437 
Feeling,  403,  419 

of  mo\ement,  329 
Feelings,  408 

Female  generative  organs,  430 
Ferments,  30,  178 
Fertilization,  439 

period  of,  after  coitus,  441 
Fetal  life,  449 
Fetus,  respiration  of,  128 
Fibers,  neural,  56 
Fibrillary  contraction,  78 
Fibrils,  neural,  56 
Fibrin,  262 

globulin,  261 
Fibrinogen,  30,  261 
"Fidgets,"  335 
Fifth  nerve,  88,  75,  177,  180 
Fimbria',  432 

"Fire"  as  well  as  "clay,"  399 
First  heart -sound,  291 

ner\e,  88,  363 
Fissure,  longitudinal,  68 

liolando,  69 

Svlvius,  69 
Flagella,  40,  440 
Flavors,  3(J0 

Flexion  and  extension  in  feeling,  409 
Fhiidity  of  tissue-protoplasm,  17,  26 
Foam-theory  of  protoplasm,  24 
Food  needs   for  various  degrees  of  lalior, 

144 
Food-cvcles,  134 
Foods,"l33 

digestibility  of,  136,  149,  151 

general  nature  of,  133 
requirements  in,  136 

heat-value  of,  143 

necessary  quantity  of,  144 

variety  of,  145 
I'oramen  ovale,  347 
Foramens  of  Luschka  and  Majemlie,  62 


Forced  movement,  75 

I''ourth  nerve,  88 

Fovea  centralis,  339 

Franklin.  Mrs.,  theory  of  color-vi.sion,  344 

Freckles,  313 

Freezing-point  methoil,  223 

Frog,  alimentary  canal  of,  172 

ner\ous  system  of,  481 

respiration  of,  477 
Fruits,  137 

"Fimction"  of  mind,  400 
Functions  of  protoplasm,  34 
Fundus,  gastric,  183 
Fusion  in  mental  function,  405 


G 


Gal.\cto.se,  30,  32,  154 

Galvanic  electricity  as  a  stinuilus,  483 

Galvanotaxis,  518 

Galvanotropisjn,  518 

Ganglia,  spinal,  93 
sympathetic,  94 

Gangiiated  cord,  93 

Gases,  action  of  various,  on  the  heart,  508. 
j  in  the  alimentary  canal,  30 

partial  pressures  of,  119 
tension  of,  118,  221 

Gastric  digestion,  188 
I  fistula,  188 

juice,  186 
mucosa,  182,  187 

Gelatin  as  food,  139 

General  ideas,  417 

Generation,  428 
I  spontaneous,  19 

I  Germ-plasm,  marvel  of,  47 

Gestation,  442 

Giant-cells,  269 

Gills,  102 

Gizzard,  185 

Glands,  224,  226 

classification  of,  22<) 
diagram  of,  224 
!  ductless,  225 

I  motor  control  of,  55' 

I  terminations  of  nerves  in,  61,  224 

i  Globin,  30 

Globulins,  .30 

Glomeruli,  244.  24() 

Giosso-pharvngeal  ner\e,  88,  ISO 

Glottis,  395" 

;  vocal  movements  of,  395 

I  Glucoproteid,  30,  31 

Glvcerin,  206 

Glycogen,  133,  208,  383,  385 
osmosis  of,  529 

Glvcosuria  in  pregnancv,  444 

Gdblet-cells,  198 

Golgi-Mazzoni  corpuscles,  356 

Graafian  follicles,  432,  437 

Grandrv  corpu.scles,  354 

Gray  matter,  58,  62,  67 

Grovia,  37 


542 


INDEX 


GroMh,  44,  219 
Gum,  animal,  30 
Gustator3'  apparatus,  359 

cells,  359 

center,  73 

nerves,  359 
Gut.     See  Intestine,  107. 
Gyri,  67 


Habit,  413 

function  of,  414 
Habitual  voluntary  movements,  388,  392, 

411 
Hairs,  326 

sudden  blanching  of,  325 
uses  of,  326,  354 
Hallucinations,  425 
Head-movements,  339 
Hearing,  345 

Heart.  278,  286,  288,  291,  293,  499 
accelerator  nerves  of,  294 
capacity  of  cavities  of,  279 
cause  of  contractions  of,  293 
changes  in,  in  pregnancy,  444 
contraction  of,  always  maximal,  500 
frequency  of  action  of,  286 
ganglia  of,  294,  499 
influence  of  respiration  on,  114,  280 
inherent  beat-rtiythm,  501 
inhibition  of,  295 
lympli-,  .508 
of  Daphnia,  466 
sequence,  or  cycle  of,  288 
sounds,  291 

Stannin's  experiments,  499 
tonus,  293,  299 
valves  of,  275,  289 
work  of,  279 
Heart-cells,  278 
Heart -centers,  297 
Heart -muscle,  293,  278,  382,  499 
Heart-walls,  circulation  in,  292 
Heat   animal,  228 

and  cold,  relations  of,  to  contraction, 

495 
centers,  365 

mechanism  of  production  of,  235 
sense,  364  i 

8p«jts,  365 

unit,  142  I 

values  of  foods,  140  I 

Height  in  ciiildhood,  450  ' 

Hf-matin,  .30,  256 
Hemispheres,  63,  517 
Hemoconia,  270 
Hf;mf)glol.iri,  113,  256 

comp^junds  of,  witli  oxygen,  carbon 
monoxide,  and  nitrous  oxide,  257 
Hemo[)liilia,  260 

Hepatic  functions,  209,  210  I 

Heredity,  47  I 

Hibernation,  236,  457 
[liccf.ugh,  125 


Honiotlierms,  229    b-y^  ^ 
I  Human  digestive  meclianism,  172 
I  temperature,  230 

!  Hunger,  372 

Hydra,  34 

Hydrobilirubin,  253 

Hydrochloric  acid,  194 

Hydrolysis,  178,  189 

Hydrosol,  protoplasm  a,  25 

Hylozoism,  18 

Hypermetropia,  527 

Hyperopia,  527 

Hypophj'sis  cerebri,  228 


Ideas,  416 

Ideation,  414,  420 

Idiosj-ncrasy,  158 

Ileo-cecal  valve,  209 

Ileum,  197 

Illusions,  425 

Immortalitj',  458 

Impregnation,  437 

Impulse,  nervous,  97,  98,  511 

Incompetency  of  the  aortic  valve,  474 

of  the  mitral  valve,  474 
Individual  death,  457 

differences  in  taste  and  smell,  364 
Indol,  2.52 

;  Induced  electricity  as  a  stimulus,  484 
j  Inductorium,  470 
Infanc}^,  449 
Infundibula,  103,  105 
Infusion  of  salines,  275 
Infusoria,  18,  etc.,  459,  461 
mental  process  of,  421 
Inherent  beat-rhythm  of  heart,  501 
Inliibition,  295,  516 

by  afferent  impulses,  513 
"Inorganic"  salts,  30,  33 

absorption  of,  217,  218 
excretion  of,  246 
metabolism  of,  220 
Inspiration,  108 

muscles  of,  108 
Instinct,  413 
Intellection,  414,  420 
Intelligence  dependent  on  hemispheres, 

518 
Intercostal  muscles,  108 
Internal  capsule,  64,  68 
ear,  347 
"radience,"  399 
secretions,  225 
Intestinal  digestion,  197 
duration  of,  199 
juice,  207 
movements,  199 
villi,  198.  203 
Intestine,  large;,  209 

movements  of,  210 
small,  197 

movements  of,  199 


INDEX 


343 


Intracardiac  inhibitory  mechanism,  517 
Invert-sugar,  194 
Ions,  25,  222,  259,  363 
Iris,  343,  521 

movements  of,  343 
Iron,  30,  256 
Irradiation  in  cortex,  71 
Irritability,  37 
Island  of  Reil,  64,  72 

of  Langerlians,  205,  226 


James,  William,  351,  401,  409 
Jejunum,  197 

Joints,  afferent  endings  in,  332 
Judgment,  418 


Karyokinesis,  45.     See  Mitosis. 
Katabolism,  220 
Kellar,  Helen,  350,  361 
Kidneys,  245,  248 

internal  secretion  of,  228 

work  of,  228,  240 
Kinase,  204 
Kinesthesia,  329 
Kinesthetic  centers,  71,  334 
Knowing,  414 
Knowledge,  417 
Krause,  end-bulbs  of,  330 
Kymograph,  472,  473 


Labor,  446 

Laboratorj'-physiology,  459 
Labyrinth,  bony,  347 

distribution  of  nerves  in,  347 

membranous,  347 
Lactation,  447 
Lacteals,  218 

absorption  b}',  218 
Lactic  acid,  241 
Lactose,  30,  32,  154 
Langerhans,  islands  of,  205,  226 
Language,  396,  417,  420 
Lanolin,  322 

Lantermann's  segments,  57 
Large  intestine,  209 

movements  of,  210 
nerves  of,  210 
Laryngeal  nerves,  396 
Larynx,  395 

Latent-periods  of  muscle,  482,  495 
Laughter,  409 
Lecithin,  30,  32 
Lens,  341 

Lenses,  optical,  524 
Leucin,  204 
Leukocytes,  257,  266 

functions  of,  268 


Leakocytes.  migration  of,  269 

number  of,  268 
Leukocytosis,  268,  444 
Levulose,  218 

Lieberkiihn,  follicles  of,  198 
Life  characterized  by  movement,  38 

origin  of,  18 
Light,  42,  344 

organ.  42,  43 

protection    from,    by  pigmentation, 
326 

vibrations,  337 
Linin,  22 
Lipase,  194,  206 
Lipochrome,  30,  156 
Liver,  209,  210 

excretory  action  of,  209 
Load,  influence  of,  on  contraction,  494 

normal,  of  muscle,  495 
Lobules,  lung,  104 
Local  sign,  351,  357 
Location-sense,  351 
Locomotion,  392 

centers  of,  74,  78 
Longitudinal  movements  of  gut,  199 
Lungs,  105 

capacity  of,  106 

of  the  chameleon,  477 
Lj-^mph,  254 

as  lubricant,  274 

composition  of,  255 

corpuscles  of,  266 

flow,  causes  of,  306 
in  childhood,  451 

glands  (nodes),  267,  306 

heart  of  frog,  508 

movements  of,  306 

origin  of,  271 
Lymphatics,  305,  308 

valves  of,  308 
Lymphocytes,  266 
Lymph-spaces,  307 


M 


Macula  acustica,  347 

lutea,  337 
Magnification  of  lung-area  by  alveoli,  105 

of  gut-area,  bv  Anlli,  199 
Maltose,  189 
Mammary  glands,  447 

lymphatics  of,  309 
secretion,  447 
Manometers,  285 
Margin  of  safety  in  diet,  140 
Marrow  of  the  laones,  266 
Mast-cells,  267 
Mastication,  176 

muscles  of,  176 
Maturity,  453 
Maximum  stimulus,  485 
Meats,  136,  149 

Mechanics  of  the  circulation,  472 
Medulla  oblongata,  75,  76.  88 


544 


INDEX 


MechiUarv  sheatli,  o7 
Moirakarvocytes,  2()!) 
^Meibomian  glands.  322 

secretion  of,  322 
Meissner,  corpuscles  of,  352 
Menil:)rana  basilaris,  348 

tvmpani,  34S 
Memory,  400,  421 
Menopause,  345 
Menstruation,  435 

relation  of,  to  o\ulation,  437 
uterine  phenomena  of,  436 
Mental  attitude  toward  pregnancy,  445 

function,  399 
Mentation,  399 

in  childhood,  453 
Metabolism,  35,  218 
Metaphase,  4(i 
Metaplasm,  22 
Metric  measiu'es,  533 
Micelhv,  24 
Micturition,  249 

nerves  of,  250 
Mitldle  age,  453 

ear,  347 
Migration  of  leukocytes,  268 
Milk,  154 

composition  of,  154 

globules,  1.55 

modification  of,  154 

secretion  of,  224 

sugar,  30,  154,  194 
Millimeter-rule,  535 
Mirrors,  520 
Mito.sis,  45 
Mononuclears,  267 
Morning-sickness,  444 
Motor  cortical  zone,  70 

nerve-cells,  59 
Mo\ement,  37 

ameboid,  38,  49 

bodil}-  and  mental,  418 

ciliary,  39 

mu.scular,  40,  373 

of  protoplasm,  37 

secretory,  41 

streaming,  38,  48 
Mucin,  31,  253 
Mucous  glands,  198,  224 

membranes,  224 
Mucus,  198 

Muscarine-poisoning,  .507 
Muscle,  373 

action  in  childhood.   151 
tli(!ories  of,  3S3 

afferent  organs  in,  329 

chemistry  of,  382 

evolution  of,  374 

fatigue-  of,  370,  490 

food,  383 

in  Daphnia,  468 

in  old  age,  4.55 

involuntary,  or  vegetative,  377 

modes  of  action  of.  3S3 

nervou.s  .service  of,  .381 


Muscle,  properties  of,  376 

smooth,  377 

structiu-e  of,  376 

universality  of,  374 

vascular  service  "of,  381 

vegetative,  377 

voluntary,  378 
Muscle-currents,  491,  492 
Muscle-nerve  preparation,  480 
Muscle-plates,  499 
Muscle-spindles,  331 
Muscular  contraction,  383,  482 

control,  333 

fatigue,  490 

movement,  44 

sense,  329 

tonus,  390,  491 

Avork,  497 
Muscularis  muco.sie,  196,  197 
Myelin  sheath,  57 
Myelocytes,  267 

of  bone,  267 
Myo-albumin,  30 
Myogenic  theory,  293 
Mvogram,  analvsis  of,  482 
Myoids,  373 
Myopia,  526 
Myosin,  382 
Myxedema,  227 

N 

Nails,  326 
Nausea,  372 

Necrobiosis,  electricity  developed  in,  492 
NerA'e-cells,  58,  59 
fatigue  of,  58 
Nerve-centers,  nature  of,  297 

sensory,  71 
Nerve,  experiments  on,  509 

effect  of,  depends  on  connections,  510 
fillers  and  fibrils,  56 
impul.se,  97 

speed  of,  98,  511 
muscle  preparation,  480 
net,  56 

rings  of  Bonnet,  351,  355 
Nerves,  action  of  electricity  on,  512 
of  motor,  54 
of  sensorj^,  54 
cranial,  88 
regeneration  of,  5(3 
sensorv  terminations  of,  327 
spinal,'  89 
Nervous  poiuhietion,  rapidity  of,  9S',  511 
ruiK'tioii  in  Daphnia,  467 
shock,  518 
•system,  52 

divisions  (jf,  63 
general  functions,  53 
more  irritable  in  pregnancy,  444 
protopla.smic  bridge,  53 
Network,  neural,  53 
\eural  axis  of  eml)r>'o,  .52 
|)r()(,()|)l;isiii,  61 


moEx 


545 


Neuraxis,  oO 

Xeuraxones  con:luct  in  botli  directions 
510 

practically  unfatiguable,  51-1 
Xeurileniiua,  57 
Neurogenic  theory,  203 
Neuro-muscular  mechanism,  3134,  387 

spindles,  332 
Neurone,  55,  60 

theory,  60 
Neurotendinous  end-organ,  332 
Neutrophiles,  267 
New  voluntary  movements,  411 
Nicotin,  168,  507 
Ninth  nerve,  88,  180 
Nissl-bodies  or  -granules,  58 
Nitrogen,  19 

determination  of,  242 

elimination  of,  240 

excretion  of,  240 

food-cycle,  134 

in  protoplasm,  19,  26 
Nodes,  lymph,  267, -306 

of  Ranvier,  57 
Noise,  perception  of,  346,  350 
Non-polarizable  electrodes,  471 
Non-vegetative  reflexes,  84 
Nose,  103 

Nuclear  spindle,  46 
Nucleic  acid,  importance  of,  27 
Nuclein,  30 
Nucleoplasm,  21,  30 
Nucleoproteid,  30 
Nucleus,  21,  22,  30 
Nursing,  frequency  of,  448 
Nutrition,  35,  214 

external,  215 

in  childhood,  450 

in  Daphnia,  467 

in  old  age,  454 

internal  (metabolism),  218 
triangle,  35 


Objective  experience,  415 
Obstructions,  perception  of,  351 
Odoriferous  particles,  363 
Odors,  363 
Old-age,  454 
Olein,  31 
Olfaction,  361 
Olfactorv  cells,  361 
center,  73,  363 
lobes,  73 

nerve,  88,  362,  363 
Olivary  body,  76 
Open    windows,  school-room   ventilation 

by,  132 
Optic  nerve,  fibers  in,  339 
tracts,  72,  88 
thalami,  74 
.  Optics,  520 
"^rgan  of  Corti,  348 
35. 


(Jrigin  of  life,  18,  19 
Ornamentation,  325 
Osmosis,  118,  221,  273,  529 
Osmotic  pressure,  223 
Ossicles  of  the  ear,  347 
Ovaries,  434 

internal  secretion  of,  228,  437 
Oviposition,  441 
Ovulation,  432 

and  menstruation,  relation  of,  437 
Ovum,  432 

discharge  of,  432 

fertilization  of,  439 

maturation  of,  433 

rate  of  movement  of,  432 
Oxidation  in  the  body,  101,  251 
Oxygen  in  protoplasm,  34 

in  respiration,  103 


Pacini,  corpuscles  of,  330,  353 
Pain,  366 

apparatus,  367 

distribution  of,  368 

lowers  blood-pressure,  286 

vs.  unpleasantness,  366,  409 
Pains  of  labor,  446 
Pabnitin,  31 
Pancreas,  205 

enzymes  of,  204 
Pancreatic  juice,  204 
Paramecium,  38,  461 
Parasites  kept  out  by  skin,  315 
Parathyroids,  227 
Parotid  gland,  172 
Particle  of  protoplasm,  27 
Parturition,  446 

nerves  of,  447 

neuromuscular  apparatus  of,  447 
Patheticus,  88 
Pepsin,  191 
Peptones,  192 
Perception,  415 

of  light,  344 

of  space,  345 
Perfusion  of  heart  with  salines,  503 
Perimeter-chart,  338 
Peripheral  plexuses,  93 
Peristalsis,  199 
Peritoneum,  275 
Perivascular  plexus,  61 
Permeability  of  capillaries,  272 
Personality  of  consciousness,  402 
Perspiration,  252,  317 
Pever's  patches,  198 
Pfliiger,  19 
Phagocytes,  268 
Pharvnx,  179 
Philodina,  463 

Phosphorus,  importance  of,  27 
Phrenics,  112 
Phrenology,  69 
Physical  exercise,  274 


540 


INDEX 


Pliy.sical  structure  of  protoplasm,  23 
Physiologic  anode  aiul  cathode,  498 
]'ia  mater,  62 
I'igeon's  milk,  322 
I'igment-cells,  324 
Pigmentation,  324 

in  pregnancy,  445 
Pineal  gland,  75^  3S() 
Pitch,  350 
Pituitary  body,  22S 
Placenta,  expulsion  of,  447 
Plane  mirrors,  520 
Plasma.  255 

Plasticity  of  protoplasm,  47 
Pla.stids.red,  263 
matelets,  258,  269 

Pleasantness  or  impleasantness  of  emo- 
tion, 409 
Pleasure,  369 

end-organs,  368 
Pleura,  116 
Plexus,  perivascular,  61 

peripheral,  94 

prevertebral,  94 
Pneumatics  of  respiration,  476 
Pneumogastric,  88,  111,  199,  295,  516 

action  on  abdominal  viscera,  199,  210 
Pnemnothorax,  477 
Poikilotherms,  229 

temperature  of,  229 
Polar  inhil)ition  in  heart,  506 

stimulation,  498 
Pole-changes,  471 
Polymorphonuclears,  267 
Polvnuclears,  267 
JV)lypeptids,  192 
J'ons  \arolii,  75 
Posterior  roots,  91 
Posture,  390 
Postganglionic  fibers,  95 
J'reganglionic  fibers,  95 
J'rcgnancv,  442 

diet  in,  1.58 

duration  of,  441 

ectopic,  433 
I'resbyopia,  527 
Pressure  in  the  hcail.  290 
J'ressure-sense,  351  ' 

Prexertebral  plexuses,  93 
Prisms,  521 

Production  of  energy,  42 
i'ro  peptones,  192 
IVophases  of  mitosis,  46 
I'roportion  of  diet's  components,  145 
I^rostate,  438 
1 'rot amine,  438 
I'rrjteclion  hv  the  skin,  313 
I'rotein.  27,  29,  30 

emjjirical  formula-  of,  28 
osmosis  of,  529 
i'rofhroMibiri,  2(i2 
Prf)to-ali)Umo.se,  192 
i'rotoplasm,  17,  459 

a  morjjhological  term,  20 
I    ciicniical  composition  of,  25 


Protoplasm,  inherently  vmstable,  25,  27 
Protrypsinogen,  271 
Proximate  principles,  26,  133 

nutrient,  135 
Pseudopodia,  38,  49 
Psvchological  terms,  400 
Ptyalin,  189 
Puberty  in  the  female,  430 

in  the  male,  429 
Pulmonary  capillary  circulation,  115 

nerves.  111,  113 
Pulse,  298 

dicrotic,  472 

forms  of,  472,  474,  475 
Pulse-rate,  286 

seven  things  told  bj",  298 
Pulse-wave,  284 
Pupil,  343 

Pure  sensations,  405 
Purkinje  cells,  61,  77 
Purposi\'e  movements,  54,  71,  411 
Pyloric  valve,  185,  197 


Q 


Qualitative  adaptation  of  diets,  153 
Qualities  of  sounds,  350 
Quality  of  food,  140,  151 
Quantitative  adaptation  of  diets,  140 


RACE-suicide  and    over-civilized  women, 
445 

Rales,  127 

RanA'ier,  nodes  of,  57 

Ration,  daily,  144 

Reaction-time,  360,  412 

Reason,  418 

Receptive  apparatus  of  eye,  337 
of  ear,  348 

Reciprocal  action  between  flexion  and  ex- 
tension, 71,  398,  409 
of  thermotaxis,  232 
of  \asomotion,  237,  301 

Recoil  of  arterial  walls,  279 

Recurrent  .sensibilitv,  92 

Rectum,  211 

Reduced  eye,  338 

Referred  pain,  92 

Reflex  movements,  S3,  410 

Reflexes,  li.st  of,  84,  85 

Reflexion,  83 

Refraction,  521 

by  spectacle  lenses,  524 
in  the  eye,  526 

Refractory  period  of  heart,  504 

Regio  olfactoria,  362 

Relation  to  (Mnirpnment ,  327 

Relations  of  bod\'   and    mind,    106,   41!, 
414,  418 
.some  theories  of,  419 

Relaxation  of  auricles,  282 


INDEX 


547 


Ht'inak,  Hbers  of,  o7 

Kennin,  192 

Repair,  organic,  219 

Repression  of  organic  emotional  reactions, 

409 
Reproduction,  44,  428 

asexual,  428 

of  Ainel)a,  50 

of  Dapluiia,  468 

sexual,  428 
Reserve  air,  128 
Residual  air,  128 
Respiration,  :M,  100 

changes  of  the  blood  in,  113,  115 

consumption  of  oxvgen  in,  101,  113 

cutaneous,  129,  328 
.    diffusion  of  air  in  limgs,  1 17 

exhalation  of  carbon  dioxide  in,   lOl 

experiments  on,  476 

external,  100 

in  Ameba,  50 

in  amphibians,  130 

in  childhood,  4.52 

in  Daphnia,  4(57 

in  old  age,  455 

in  the  excised  tissues,  101 

in  the  fetus,  128 

in  hibernation,  236 

inhalation  of  poisonous  gases,  257 

internal,  113 

intestinal,  130 

meclianism  of,  103 

movements  of  Ameba  tlependent  on, 
50,  109 

nerves  of,  111 

organs  of,  103 

of  pure  oxygen,  103 

rates  of,  in  various  animals,  124 

relations  between  the  oxygen  con- 
sumed and  the  carbon  dioxide  ex- 
haled, 103 

sounds  of,  125 

soiH'ces  of  carbon  dioxide  in,  251 

through  the  skin,  129,  323 

volumes  of  inspired  and  expired  air, 
103,  128,  131 
Respiratory  centers,  111 

exchange,  daily,  103 

quantities,  128 

soimds,  125 
Rest,  421 

Restiform  body,  76 
Retardation  of  circulation,  282 
Retina,  336 
Rheocord,  471 
Rheotaxis,  43,  441 
Rhodopsin,  337 
Rhythm,  cardiac,  286 

respiratory,  120 
Rhvthmic  segmentation,  201 
Ribs,  109 
Rigor  mortis,  382 
Rod-cells,  337 
Rods,  ,337 
Rolandic  area,  70 


Rontgen  ra\s,  product  inn  of  aspci'niia  bv, 

439 
Roots,  anterior,  90,  510 

])Osterior,  91,  510 
Rotation-point,  340 
RouikI  ligament,  439 
Ruffini,  nerve-endings  of,  365 
Ruminant's  stomach,  183 
Running,  393 


Saccharoses,  30 

Sacral  system  of  the  autonomics.  97 

Saliva,  173 

action  of,  on  starch,  189 

mechanical  action  of,  178 
Salts,  "inorganic,"  30,  33 

absorption  of,  217,  218 
excretion  of,  246 
metabolism  of,  220 
Sarcolactic  acid,  241 
Sarcolemma,  380 
Sarcomeric  imbibition,  384 
Sarcostvles,  380 
Savors,"363 

Schneiderian  membrane,  359,   362 
Schwann,  sheath  of,  57 
Sebaceous  glands,  321 

matter,  321 
Sebum,  321 

composition  of,  321 

uses  of,  322 
Second  heart-sound,  292 

nerve,  88,  339 
Secretin,  253 
Secretion,  41,  220 

change    in    the    circulation    of    the 
glands  during,  224,  301 

control  by  sympathetic,  95 

mechanism  of,  220,  224 
Secretions,  classification  of,  224 
Segment,  neural,  79 
Semen,  438 

Semicircular  canals,  346,  347.  369 
Senescence,  454 
Senility,  diet  in,  158 
Sensation,  404,  415 

ninnber  of  varieties  of,  404 

of  the  skin,  316 
Senses,  327 

in  old  age,  456 

of  Ameba,  49 

of  children,  4.52 

of  Daphnia,  467 
Sensory  cortical  zone,  71 
Sequence  of  cardiac  events,  288 

of  respiratory  e\"ents,  116 
Serum-albumin.  30,  255 
Serum-globulin,  30,  115 
Seventh  ner\e,  88 
Sexual  desire,  occasion  of,  439 
Sheath  of  Schwann,  57 
Sighing,  125 
Signal,  472 


o4S 


IXDEX 


Sitting.  392 

Sixth  nerve,  88 

Skatol,  252 

Skill,  neuromuscular,  389 

Skin.  312 

absorption  by,  323 

diagram    of     the     functions    of, 

312 
reflexes,  84 
Sleep,  421 
Small  intestine,  197 

h-mphatics  of,  305 
movements  of.  199 
nerves  of,  198,  202 
Smegma  of  the  prepuce  and  of  the  labia 

minora,  321 
Smell.  361 

apparatus.  361 
functions  of,  103.  361 
nerves  of.  363 
Smooth  muscle,  377 

contraction  of,  4S6 
Sneezing,  125 
Sniffing.  125,  362 
Sobbing,  125 
Sodiimi  chloride,  33 

osmosis  of,  529 
Somesthesia,  329,  351 
Somesthetic  areas,  72 
Sonorous  Aibrations,  345 
Sounds  of  the  heart,  291 
musical,  350 
physics  of,  345 
^-ibrations  of,  346 
Souring  of  milk,  157 
Space-perception,  345 
Special  muscular  functions,  390 
Speech,  394 

center,  72,  75,  396 
mechanism  of,  86,  394 
Speed  of  blood,  282 

of  human  pulse-wave,  475 
Spermin,  438 
Spermatozoa,  440 

movements  of,  441 
Spermatogenesis  under  erotic  influences, 

439 
Spherical  aberration,  524 

mirrors,  520 
Sphygmogram,  brachial,  472 

normal.  473 
Sphygmograph,  472 
Sphygmomanometer,  285 
Spinal  accessory,  88,  180 
animal.  84 
cord,  79 

colunm.s  of,  76,  80 

connection  of,  with  the  enceph- 

alon,  75.  76 
direction  of  fibers  in,  80 
general  functions  of,  80 
motor  and  sensory  paths  in,  84, 

89 
plan  of  the  nerves  of,  79 
reflex  centers  in,  85 


i  Spinal  cord,  relations  of,  to  muscular  co- 
]  ordination,  86 

I  vasomotor  functions  of,  513 

ganglia,  93 
nerve-roots,  510 
nerves.  89 
Spindle  in  karvokinesis.  46 
Spleen.  266,  270 

diagram  of  theories  as  to  the  func- 
tions of,  271 
internal  secretion  of,  228 
relations  of,  to  blood-corpuscles,  266 
rliytlmiical  contractions  of.  271 
Spontaneous  generation,  18 
Spots,  temperature.  365 

touch,  355,  365 
Standing,  391 
Stannius'  ligature,  first,  499 

second.  500 
Starch,  135.  145,  189 

osmosis  of.  529 
Steam  engine  plant  r.s-.  organism.  102 
Steapsin,  194,  204,  206 
Stearin,  31 
Stenosis  of  the  aortic  vahe,  474 

of  the  mitral  valve.  474 
Stercobilin.  253 
Stereognosis,  71 

center  of.  71 
Stethogram.  477 
Stethograph.  120 
Sthenic  action  of  joy,  453 
Stomach,  180 

functions  of,  194 
glands  of,  181,  187,  196 
movements  of,  182 
mucosa  of,  182 
regurgitation  from^  186 
Stomata  in  l\nnphatics,  275 
Stream  of  consciousness,  407 
Streaming,  protoplasmic,  38,  48 
.Strength,  muscular,  389 
Structure  of  protoplasm,  24 
Strj'chnine.  action  of,  514 
Subarachnoid  space,  62 
Subconsciousness,  327,  406 
Sublingual  glands,  173 
Submaxillar\-  gland,  173 
Succus  enterious,  207 
Suction,  auricular,  282 

thoracic,  280 
Sugars,  30.  146,  190 
•Sulphocyanate  in  saliva,  174 
Sulphuretted  hj-drogen,  30,  252 
Summation  of  stimuli,  488 
Superpo.sition  of  contractions,  488 
Suprarenal  capsules,  228 
Swallowing,  180 
Sweat,  252,  317 
centers,  319 
conditions  determining  amount  of, 

319 
fibers,  91,  319 
glands,  318 
properties  and  composition  of,  318 


INDEX 


549 


Sweat,  secretion,  319,  320 
Swinging  movements  of  gut,  200 
Sympathetic  influence  on  heart,  294,  515 

plexuses,  93,  94 

system  of  nerves,  93 
Synapses,  60 
Synovia,  25(5 
Syntonin,  192 


Tables,  533 

Tactile  centers,  72,  355 

corpuscles,  351 

menisci,  354 
Tan,  313 

Tardigrade,  236,  457,  465 
Taste,  357 

and  smell,  confusion  between,  363 
Taste-buds,  358 

centers,  360 
Tastes,  360 
Taxes,  43,  518 
Tea,   161 
Teeth,  174 

eruption  of,  175 
Teleodendrites,    61 

Temperature  affects  contraction  of  heart 
muscle,  502 

of  the  body,  equalization  of,  232 
in  childhood,  452 
in  old  age,  455 

senses,  238,  364 
Tendon,  afferent  endings  in,  331  i 

Tenth  nerve,  88,  111,  199,  210,  295,  516.  , 
See  Vagus.  i 

•"Terminal  bars,"  307 
Testicles,  internal  secretion  of,  228 

product  of  the,  438  ■ 

Tetanus,  muscular,  489,  490 

not  obvious  in  heart,  502 
Thein,  160 
Theobromin,  162 

Thermodynamic  theory  of  muscle-action,  \ 

384  I 

Thermogenesis,  235  [ 

center  of,  74  ! 

Thermolysis,  237  i 

Thermometer  scales,  comparison  of,  533    ' 
Thermotaxis,  232  , 

centers  of,  239  I 

nerves  of,  238  ! 

served  by  the  skin,  317  I 

Third  nerve,  88  I 

Thirst,  371 

Thrombocytes,  258,  269 
Thoracic  suction,  280 
Thorax,  108 
Thought,  416,  420 
Threshold,  independent  of  load,  486 

of  sensation,  406 

of  smell,  363 

of  touch,  357 

stimulus,  485 


Thymus,  227 
Thyroid,  22() 

accessory,  227 

in  coitus  and  pregnancy,  445 

extirpation  of,  227 
Tickling,  369 
Tidal  air,  128 
Tigroid  substance,  58 
Time  of  circulation,  283 
Tissue-builders,  138 
Tissues,  respiration  of,  101 
Toadstool-poisoning,  507 
Tobacco,  168 
Tones,  350 

Tongue,  172,  178,  358 
Tonus  of  heart,  293,  299,  506 
Topics  for  dissertations  and  conference, 

530 
Touch,  351 

centers,  355 

nerves,  335 

spots,  355,  365 
Toxins  in  colon,  212 
Trachea,  104 
Tracts  in  the  cord,  80 
Training-effects  upon  muscle,  389 
Transmitting  mechanism  of  ear,  347 
Triangle  of  nutrition,  35 
Trigeminal  nerve,  88,  180 
Trimethylxanthin,  160 
Trochlearis  nerve,  88 
Trophism,  56,  295,  453 
True  respiration,  112 
Tryglyce rides,  31 
Trypsin,  30,  204 
Tubifex,  464 
Tuning-fork,  472 
Twelfth  nerve,  88 
Typical  meal,  147 
Tyrosin,  204,  253 

u 

Understanding,  418 
Unification,  52 
Unipolar  induction,  493 
Unity  of  consciousness,  402 

of  life,  460 
"Universalitv"  of  muscle,  374 
Urea,  241      " 

determination  of  amount  of,  241 
Ureagenic  chemism,  241 
Ureters,  248 
Urethra,  249 

glands  of,  438 
Uric  acid,  243 
Urinary  bladder,  248 

capacity  of,  249 

fimctions,  diagram  showing,  248 

secretion,  theories  of,  246 

sensitivity  of,  250 
Urine,  242 

amount  of,  243 

discharge  of,  248 

excretion  of,  240,  245 


ooO 


IXDEX 


Trine,  inorganic  salts  of,  243 
in  pregnancy,  444 

Urobilin,  253 

Urochronie,  244 

Uterus,  431,  436 

mucosa  of,  436,  442 


^'agixal  secretions,  440 

A'agus  nerve,  88,  111,  199,  210   29,5,  515 

Valves  of  heart,  291 

of  Ivmphatics,  308 

of  veins,  281,  311 
Yalvulse  conniventes,  198 
Variety  in  diet,  145 
A'ascular  functions,  297 
"N'aso-inhibitory  nerves,  303 
Vasoconstrictor  centers  and  nerves,  302 
"N'asodilator  centers  and  ner\es,  303 
Vasomotion,  300 

in  the  brain,  62 
Vasomotor  functions  of  cord,  513 
Vater,  corpuscles  of,  330 
^  egetal  cells,  21 

tissue,  21 
Vegetarianism,  148 
Vegetative  reflexes,  84 
Veins,  310 

capacity  of,  310 

characteristics  of,  310 

pressure  of  blood  in,  283,  284 

valves  of,  311 
Ventilation,  131 
Vernix  caseosa.  322 
^'ertigo,  369 
A'esicuki-  seminales,  439 
Vesicular  murmur,  126 
Viatility,  82,  83 
"N'ibrations  producing  light.  337 

sound,  346 
Villi,  198,  203 

arachnoidal,  63 
\'isceral  nerse-supply,  93 
Vbion,  335 

binocular,  339,  341 

centers  for,  72,  75 

duration  of  impressions  in,  311 

field  of,  338,  341,  34.5 

perception  of  colors  in,  344 


^'isual  centers,  72 
purple,  337 
theories,  343 
"Vitalism,"  29,  223 
"\'ocal  cords,  395 
^'oice,  anatomy  of  organs  of,  394 

action  of  accessory  parts  in,  395 
air-chambers  of,  395 
nerves  of,  395 
Volition,  410,  420 
"\'olume  of  contracting  muscle,  495 
"\'oluntary  heart-control,  296 
I  movements,  54,  71,  411 

I  Vomiting,  176 
!  Vorticella,  462 


W 


^^'ALKIXG,  392 

Wallerian  method  of  nerve-degeneration^ 

80 
Water,  excretion  of,  242,  251,  2.52 

in  nerve-protoplasm,  62 

in  protoplasm,  26 

jacket  of  the  brain,  63 

production  of,  in  the  bod}',  242 
Weight  in  childhood,  449 

of  cortical  brain-cells,  68 
White  corpuscles,  257,  266 
Will,  410,  420 

free-,  411 
Word-blindness,  397 
Word-deafness,  72,  397 
Work  done  by  a  cross-striated  muscle,  497 

bv  human  heart,  279 
Worr\-,  453 


Xaxthix,  1()1,  241 


Yawxixg.  125 
Youth,  449 


Zootiuuiiiriuni,  463 
Zymolysis,  rate  of,  179 
relations  of,  189 


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